محتاج كتلوك دوائر الكترونيه

Telephone Ring Generator Using Small Power Transformer

This ring generator will ring a telephone once every 10 seconds. The interval between rings can be lengthened or shortened by varying the value of the 1 Meg resistor. The 70 volt/ 30 Hz ring voltage is produced from the 120 volt side of a small 12.6 VAC power transformer (Radio Shack 273-1365). Both capacitors connected across the transformer windings are non-polarized / 100 volts. Circuit draws about 300mA from the 12 volt DC power supply during the ringing interval.
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LED 12 Volt Lead Acid Battery Meter


In the circuit below, a quad voltage comparator (LM339) is used as a simple bar graph meter to indicate the charge condition of a 12 volt, lead acid battery. A 5 volt reference voltage is connected to each of the (+) inputs of the four comparators and the (-) inputs are connected to successive points along a voltage divider. The LEDs will illuminate when the voltage at the negative (-) input exceeds the reference voltage. Calibration can be done by adjusting the 2K potentiometer so that all four LEDs illuminate when the battery voltage is 12.7 volts, indicating full charge with no load on the battery. At 11.7 volts, the LEDs should be off indicating a dead battery. Each LED represents an approximate 25% change in charge condition or 300 millivolts, so that 3 LEDs indicate 75%, 2 LEDs indicate 50%, etc. The actual voltages will depend on temperature conditions and battery type, wet cell, gel cell etc. Additional information on battery maintenance can be found at:


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LED VU Meter


The circuit below uses two quad voltage comparators (LM339) to illuminate a series of 8 LEDs indicating volume level. Each of the 8 comparators is biased at increasing voltages set by the voltage divider so that the lower right LED comes on first when the input is about 400 millivolts or about 22 milliwatts peak in an 8 ohm system. The divider voltages are set so that each LED represents about twice the power level as the one before so the scale extends from 22 milliwatts to about 2.5 watts when all LEDs are lit. The sensitivity can be decreased with the input control to read higher levels. I have not built or tested this circuit, so please let me know if you have problems getting it working. The power levels should be as follows:

• 1 LED = 22mW
• 2 LEDs = 42mW
• 3 LEDs = 90mW
• 4 LEDs = 175mW
• 5 LEDs = 320mW
• 6 LEDs = 650mW
• 7 LEDs = 1.2 Watts
• 8 LEDs = 2.5 watts

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Analog Milliamp Meter Used as Voltmeter


A milliamp meter can be used as a volt meter by adding a series resistance. The resistance needed is the full scale voltage reading divided by the full scale current of the meter movement. So, if you have a 1 milliamp meter and you want to read 0-10 volts you will need a total resistance of 10/.001 = 10K ohms. The meter movement itself will have a small resistance which will be part of the total 10K resistance, but it is usually low enough to ignore. The meter in the example below has a resistance of 86 ohms so the true resistor value needed would be 10K-86 or 9914 ohms. But using a 10K standard value will be within 1% so we can ignore the 86 ohms. For a full scale reading of 1 volt, the meter resistnace would be more significant since it would be about 8% of the total 1K needed, so you would probably want to use a 914 ohm resistor, or 910 standard value. The milliamp meter can also be used to measure higher currents by adding a parallel resistance. The meter resistance now becomes very significant since to increase the range by a factor of ten, we need to bypass 9/10 of the total current with the parallel resistor. So, to convert the 1 milliamp meter to a 10 milliamp meter, we will need a parallel resistor of 86/9 = 9.56 ohms.

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1 Second Time Base From Crystal Oscillator


The schematic below illustrates dividing a crystal oscillator signal by the crystal frequency to obtain an accurate (0.01%) 1 second time base. Two cascaded 12 stage counters (CD4040) form a 24 stage binary counter and the appropriate bits are gated together to produce the desired division. Using a crystal of some even multiple of 2 is desirable so that one stage of the counter automatically toggles every second which eliminates the need for the NAND gate and reset circuitry, however the circuit below illustrates using a crystal which is not an even multiple of 2 and so requires additional components. Using a 50 Khz crystal, a count of 50000 is detected when the appropriate counter bits that add up to 50000 are all high. This corresponds to bits 15 (32768) + 14 (16384) + 9 (512) + 8 (256) + 6 (64) + 4 (16). Bits 14 and 15 are the 3rd and 4th stages of the second counter, bit 0 is the first stage of the first counter (Q1, pin 9). To use a 100 Khz crystal, each bit would be moved one to the right so the total would be (65536 + 32768 + 1024 + 512 + 128 + 32 = 100,000). Using a 1 Mhz crystal, the following bits would be needed:
Bit 19 - Right counter - Q8 - pin 13 - Decimal value = 524288
18 7 4 262144
17 6 2 131072
16 5 3 65536
14 3 6 16384
9 - Left counter - 10 14 512
6 7 4 64
---------
1,000,000
At 1 Mhz, the 330K resistor in the oscillator circuit will need to be reduced proportionally to about 15K. When the terminal count is reached, a 7 uS reset pulse is generated by the Schmitt Trigger inverter stage that follows the NAND gate. The 47K resistor and 470 picofarad capacitor sustain the output so that the counters are reliably reset to zero. This is less than one clock cycle at 50Khz and does not introduce an error but would amount to 7 cycles at 1 MHz which would cause the counters to lose 7 microseconds of time per second. It's not much of an error (7 parts in a million) but it would be there. The minimum reset pulse width for the 4040 CMOS counters is about 1.5 uS, so the reset pulse cannot be made much shorter.

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32.768 KHz oscillator using a watch crystal


Below are a couple circuits you can use to produce a 32.768 KHz square wave from a common watch crystal. The output can be fed to a 15 stage binary counter to obtain a 1 second square wave. The circuit on the left using the 4069 inverter is recommended over the transistor circuit and produces a better waveform. The single transistor circuit produces more of a ramping waveform but the output swings the full supply voltage range so it will easily drive the input to a CMOS binary counter.

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Generating Long Time Delays


Generating long delays of several hours can be accomplished by using a low frequency oscillator and a binary counter as shown below. A single Schmitt Trigger inverter stage (1/6 of 74HC14) is used as a squarewave oscillator to produce a low frequency of about 0.5 Hertz. The 10K resistor in series with the input (pin 1) reduces the capacitor discharge current through the inverter input internal protection diodes if the circuit is suddenly disconnected from the supply. This resistor may not be needed but is a good idea to use. The frequency is divided by two at each successive stage of the 12 stage binary counter (CD4040) which yields about 1 hour of time before the final stage (Q12) switches to a high state. Longer or shorter times can be obtained by adjusting the oscillator frequency or using different RC values. Each successive stage changes state when the preceding stage switches to a low state (0 volts), thus the frequency at each stage is one half the frequency of the stage before. Waveform diagrams are shown for the last 3 stages. To begin the delay cycle, the counter can be reset to zero by momentarily connecting the reset line (pin 11) to the positive supply. Timing accuracy will not be as good as with a crystal oscillator and may only be around 1 or 2% depending on the stability of the oscillator capacitor.


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Telephone Ring Generator Using Switching Supply

The telephone ring generator shown below generates the needed high voltage from a simple switching mode power supply (SMPS) which employs a CMOS Schmitt Trigger square wave oscillator, 10 mH inductor, high voltage switching transistor (TIP47 or other high voltage, 1 amp transistor) and a driver transistor (2N3053). The inductor should have a low DC resistance of 1.5 ohms or less. The switching supply must have a load connected to prevent the voltage from rising too high, so a 22K resistor is used across the output which limits the voltage to about 120 DC with the phone ringer disconnected and about 90 volts DC connected. The output voltage can be adjusted by changing the value of the 150K resistor between pins 10 and 11 which will alter the oscillator frequency (frequency is around 800 Hz as shown). The supply is gated on and off by a second Schmitt Trigger oscillator (pins 12/13) so that the phone rings for about 2 seconds and then the circuit idles for about a minute between rings. These times can be adjusted with the 10K and 300K resistors connected to pin 12. The push button shown is used to manually ring the phone. The 25Hz ringing frequency is generated by another Schmitt Trigger oscillator (pins 1/2) which controls the H bridge transistor output circuit. The 6 transistors in the output stage (4 NPN, 2 PNP) should be high voltage types rated at 200 volts collector to emitter or more. The ringer will only draw around 10 mA, so the output transistors can have a low current rating but must have a high voltage rating. I used TIP47s and small signal PNPs of unknown numbers that I had on hand, but other types such as NTE287 (NPN) and NTE288 (PNP) should work. Both have a 300 volt C-E rating and cost about $0.95 from mail order houses. The two 470 ohm resistors connected to the output serve to limit the current in case the output is shorted. I never tried shorting the output to see how effective the resistors are, but I did lose a couple transistors and then decided to add the resistors. They should limit the surge to around 120 mA which should be low enough to prevent damage. The circuit draws around 250 mA when the ring signal is present so if you want to operate it from batteries, six 'D' type alkaline cells are recommended. It probably won't work with a small 9 volt battery.

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Telephone Ring Generator Using Small Power Transformer

This ring generator will ring a telephone once every 10 seconds. The interval between rings can be lengthened or shortened by varying the value of the 1 Meg resistor. The 70 volt/ 30 Hz ring voltage is produced from the 120 volt side of a small 12.6 VAC power transformer (Radio Shack 273-1365). Both capacitors connected across the transformer windings are non-polarized / 100 volts. Circuit draws about 300mA from the 12 volt DC power supply during the ringing interval.
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LED 12 Volt Lead Acid Battery Meter


In the circuit below, a quad voltage comparator (LM339) is used as a simple bar graph meter to indicate the charge condition of a 12 volt, lead acid battery. A 5 volt reference voltage is connected to each of the (+) inputs of the four comparators and the (-) inputs are connected to successive points along a voltage divider. The LEDs will illuminate when the voltage at the negative (-) input exceeds the reference voltage. Calibration can be done by adjusting the 2K potentiometer so that all four LEDs illuminate when the battery voltage is 12.7 volts, indicating full charge with no load on the battery. At 11.7 volts, the LEDs should be off indicating a dead battery. Each LED represents an approximate 25% change in charge condition or 300 millivolts, so that 3 LEDs indicate 75%, 2 LEDs indicate 50%, etc. The actual voltages will depend on temperature conditions and battery type, wet cell, gel cell etc. Additional information on battery maintenance can be found at:


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LED 12 Volt Lead Acid Battery Meter


In the circuit below, a quad voltage comparator (LM339) is used as a simple bar graph meter to indicate the charge condition of a 12 volt, lead acid battery. A 5 volt reference voltage is connected to each of the (+) inputs of the four comparators and the (-) inputs are connected to successive points along a voltage divider. The LEDs will illuminate when the voltage at the negative (-) input exceeds the reference voltage. Calibration can be done by adjusting the 2K potentiometer so that all four LEDs illuminate when the battery voltage is 12.7 volts, indicating full charge with no load on the battery. At 11.7 volts, the LEDs should be off indicating a dead battery. Each LED represents an approximate 25% change in charge condition or 300 millivolts, so that 3 LEDs indicate 75%, 2 LEDs indicate 50%, etc. The actual voltages will depend on temperature conditions and battery type, wet cell, gel cell etc. Additional information on battery maintenance can be found at:


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10. Use old phones as an intercom

I have recently thought about this and come up with a kludgy but workable scheme.
Talking over the phones is easy. You put DC current through the phone and it transmits and receives audio. So two phones and a current source (about 25mA) all in series will give you a talking circuit. A suitable current source can be as simple as a 9V battery and a series resistor whose value is adjusted (with both phones offhook) till about 25mA flows. You can then bypass the battery and the resistor with a capacitor to couple the audio straight across and get a loud and clear connection.
What is much harder is signaling the other end. To ring the bell you need to put 90V (RMS) 20Hz AC into the phone (nominally). Lower voltages will work (down to about 40V) but different frequencies won't. You can't ring the phone at 60Hz. I have a ringing circuit in a PBX I built but it consists of a 20Hz sinewave generator, a push-pull power booster and a big transformer. Much too elaborate for a simple 2-phone intercom circuit, and anyway the ringing voltage could painfully zap a kid.
So forget the bell and look into other forms of signaling. This is what I have come up with:

+ | | -
+-------+------ - - --+---||||---/\/\/--+---- - -----+-------+
| | | | | R | | |
| | | 24V | | |
| --- | | --- |
| | | +---||------------+ | | |
| --- Sonalert C Sonalert --- |
| C | | C |
+---||--+ +--||---+
| _|_, _|_ |
| / \ 15V 15V \ / |
PHONE -+- Zener Zener `-+- PHONE
| | | |
| | | |
+-------+------------------ - - - -------------------+-------+
As before, set R to give you a talking current (both phones offhook) of about 25mA. Start with 1K ohm. Leave it in if the phones work well enough; the current is not very critical. The capacitors C are audio bypass capacitors and should be about 0.47uF. When the phones are onhook they present an open circuit, and the 24V battery voltage is not enough to overcome the 30V series drop of the Zeners and no current flows. When both phones are offhook they present a very low resistance and the talking current (determined by R) flows.
When only one phone is offhook it places its low DC resistance across the Zener diode on its side so that the full 24V supply is applied to the other side. This overcomes the voltage drop of the other Zener diode so the other Sonalert beeps. The wonderful thing about Sonalerts is that they make a loud noise with only a few milliamps of current so the series resistor R doesn't matter. Especially nice is a pulsing Sonalert which goes "Beep beep beep" automatically. While the far-end Sonalert is beeping, you hear the beeping in the near-end receiver (at low volume thanks to the bypass capacitor across the far-end Sonalert) to confirm that the line is working and the other end is being signaled.
The power supply can be three 9V batteries in series but since 80% of the power is lost in series resistor R rather than in powering the phones it seems a little wasteful. A 24V wall wart with clean filtering would be better.
The signaling components can be mounted inside the phones. Only two wires are needed to go to each phone, and the power supply can be mounted centrally, out of harm's way. If R is adequately big (1/2 watt) and has enough ventilation then both lines can be indefinitely shorted out without any fire hazard and there is not enough voltage anywhere to hurt anyone.
I have tested this with 500-type phones and two different types of piezo buzzers (pulsing sonalerts and non-pulsing brand X ones) and it works great. You should be able to get all the needed parts including piezo buzzers at Radio Shack. I love telephones. Too bad I don't have any kids who want an intercom line.
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1. Telephone in use light


+----+-------------+-------+-------- +9VDC
| | | |
| | |\ R5 R6
| +-------|-\ | |
| | | >--+ LED1
| | +--|+/ | v
^ | | |/ | |
CR2 R4 | | C+
| | | |\ | | /
<+>--R1--+--R3--+----+--> | <--+--|-\ | |/
| | | | | >--+-B-|
phone | | | +-------|+/ |\
line | | ^ | |/ | \
R2 C1 CR1 CR3 E+
| | | v U1 Q1 |
| | | | |
<->------+------+----+----+---------------------+-------- GND

R1,R2 1 Meg
R3 10 K
R4 1 K
R5 4.7 K
R6 470 ohm
C1 .005 uF
CR1-3 1N914 diode
LED1 any old led
Q1 2N2222 or 2N3904
U1 LM339 quad comparator (be sure to connect power and ground)
--> <-- are connected (jump)
^ or v cathode of diode
+ connection
9VDC any old 9VDC wall transformer works nicely
Circuit description R1 and R2 form a voltage divider, insuring that the phone line sees a high impedance load and that high voltages (such as the ring voltage) are easily dissipated by the protective diodes (CR1 and CR2). Also (obviously) they serve to divide all incoming voltages by two. Capacitor C1 filters out some of the audio signals that might otherwise make the LED flicker with speech.
The voltage across a busy line is generally 5-10 volts, whereas a free line sits at more like 48 volts, and a dead line (definitely not in use!) sits at 0. This circuit uses two comparators (sections of U1) to detect when the voltage is either too high or too low. Normally Q1 is kept turned on by pullup resistor R5, keeping LED1 illuminated. If either comparator detects incorrect voltage, its open-collector output goes into saturation and forces Q1 (and thus the LED) off.
The top comparator section has its negative input connected to the +9V supply, so it will force the LED off if the voltage at its positive pin should exceed 9V. Remember that we are dividing by two, so the phone line voltage would have to exceed 18V in order for this comparator to force the LED off. This would normally happen when the phone is not in use (48V, remember?).
The bottom comparator section has its positive input connected to the anode of a forward biased silicon diode, so it is sitting at 0.6V. If its negaive pin is ever lower than 0.6V, this comparator's output will go into saturation and force the LED off. Remember, again, that we are dividing the phone line voltage by two, so the phone line voltage would have to drop below 1.2V in order for this comparator to turn off the LED. This is clearly a dead line.
Serving Suggestion: Install the circuit in an out-of-the-way place, then connect the collector pin of Q1 and the +9VDC to unused (yellow or black) conductors in your home or office phone wiring. Then you can place additional LEDs (with current limiting resistors like R6) at each phone. I once used a power transistor for Q1 and peppered our electronic repair shop with LEDs at every workstation.
If you have any difficulty understanding my ascii art, the circuit theory, or anything about this posting, please feel free to contact me.

2. Detecting a telephone RING


When a phone line rings, there's 90 V RMS AC at 20 HZ on the line. It's enough to give you a jolt you won't soon forget. Thus, it's hard to miss!
My favorite detection scheme looks like this. This is off the top of my head so you may have to twiddle component values a bit. Also, this is for driving logic circuits. I'll treat your specific problem in a bit.
Detector Schematic

+-------------------------- + DC power supply
|
^
CR2
|
O---C1--+--R3---+--CR3>-+-------+-------+-----> ring det logic
| | | |
phone R2 ^ C2 R1
line | CR1 | |
| | | |
O---------------+-------+-------+-------+----- GND

C1 .1 uf
CR1,CR2,CR3 1N914
C2 10 uF
R1 100K
R2 10K
R3 100K
Mostly, there is only DC or small signal AC (audio) on the phone line. C1 blocks the DC, and the R3-R2 voltage divider prevents the low level AC from having any effect. When the ring signal comes along (90V RMS) enough voltage is developed at the juncture of R3 and R2 that some charge is pumped into C2 via CR3. Protective diodes CR1 and CR2 ensure that the output of this circuit will not grossly exceed the power supply levels and thus damage the logic circuits it may drive.
C2 and R1 have a time constant of 1 second, so one second after each ring ends, the output will fall to a logic zero again. This circuit could easily drive a counter, to count rings. A timer with a longer period could be used to reset the counter if no rings have come in within say 10 seconds.
For the specific problem in the post I'm answering, (" LED should stay ON while the phone rings") you would want to change the design somewhat. Here's how I would make a ring indicator light that stays on until the phone acutally stops ringing:

O---C1--+--R1---+--CR2>-+-------+--R2---+
| | |
phone ^ C2 LED1
line CR1 | v
| | |
O-----------------------+-------+-------+

C1 1 uF, decent voltage
C2 see text
R1 10 K
CR2 1N914
CR1 zener -- 9v or higher
R2 1 K
LED1 any old LED
I haven't built this, but here's my theory: C1 blocks DC, R1 limits the current that the ring voltage could cause. The ring voltage is rectified by CR2, filtered by C2, and limited in amplitude by zener CR1. Then the charge stored in C2 is slowly used to light LED1. As long as C2 is large enough (I'd start with 10 uF and experiment from there) to keep the LED on between rings, and small enough that the LED goes off within a reasonable amount of time after the last ring, you're set.

I took ideas from schematics posted here a few days ago and constructed a telephone "line in use" indicator. Here's the circuit...

----> (to +5)
1M 1k / E
>----- -----\/\/\----+---\/\/\-----|
| \ C
\ |
/ 220k \
from \ / 1k
phone bridge | \
line | |
| LED
| |
>------ --------------+---------------+
|
GND
The transistor is a PNP Motorola 3638 with hFE of around 100 (probably doesn't matter). Also, you could use this with different supply voltages if you change the 220k resistor. Also, in case anybody's interested, I found the on-hook open-circuit voltage of my phone line to be 48.7V, and the short circuit current to be 72.8mA. This leads to the conclusion that the line has a resistance of about 670 ohms. There have been a few calls recently in sci.electronics for phone in use circuits (ie a circuit that lights a LED when an extension phone is off hook).
Following are two circuits I archived some time ago from sci.electronics. The first appears pretty complete and requires an external 5V power supply. The second seems to be a loop current trap that enables you to move from one extension phone to another without leaving the first phone off hook. I don't know how well either of these circuits work as I haven't actually built them.


I thought I would try to post the schematic. This circuit requires a separate 5 volt supply. The branch of the circuit that contains C1, C2 & R5, R6 is only used as a passive tap. (So you can record the line when the rest of the circuit says 'off hook'. It can be removed if not needed. If used, it can directly drive a microphone input to a portable recoreder.
The Output of Q2 completes a path to ground when the phone lines gives an off hook reading. This can drive a relay (for a tape recorder motor) or an LED. Be sure to include a current limiting resistor if an LED is used. Also, D1 may be ommited if a non-inductive load is used (Relays and incandescent (sp?) lamps are inductive)
The LED thingy like this that I made for my phone flashes nicely when the phone rings (at the 20..25 Hz ring freq), so I can turn the ringer off, and still get silent ring indication (a feature, not a bug)
Well, its not exactly postscript(tm), but if you stand back and squint, you'll get the idea.

<----+-R5-+ +----------+--------* +6vdc (I use 5 volts)
| | | |
R6 | | D1___
| | R3 / \
| | | | ___
<----+ | | +--------> Out
| | | Q2|/
C1= C2= BR1 +-R8-+---|
| | R1 __ Q1|/ | |\v
*----+------/\/--| |--+--+---| R4> |
| |~+|R7<C3L |\v < |
| R2 |~-| > T | | |
*---------+-/\/--|__|--+--+-----+----+-----+--------* Ground
|_
///

R1, R2 2.2M Reproduced (kind of) without
R3, R4 470K permission. Copyright 1980
R5 470 TAB BOOKS Inc.
R6 100
R7 100K
R8 220K
C1, C2 0.01uf, 100V
C3 1.0 uf
BR1 Full wave Bridge Rectifier, about 200 VDC (or higher)
D1 HEP R0052 (I use 1N400*)
Q1, Q1 HEP S9100 -or- NTE-172a

My computer is in the basement and this device tells me if the phone line is in use. I have inserted a N/O switch in the battery connection so that the batteries will last longer as sometime my sons spend a lot of time on the phone. Prior to using my modem I press the switch to find out if the line is busy.

2N3906 33K 2N3904

2.2 meg /----------/\/\/\---+ /------+
|/ | |/ | ***
Tip o--/\/\/-----+-------| PNP +----| NPN \ 220
\ |\ | \ /
/ 330K | | \
\ | +-------------+ |
Ring | | | | ---
o--/\/\/-----+ | O - | / \ Led
2.2 meg | | 3V | |
| | O + | |
| | | | |
+-------------------------------------+ |
| | |
+-------------+-------------------+
** This resistor may have to be lowered to match the led used. Use alkaline battery, they last longer.
3. (manual) Phone In-Use Light



>>-----------------+------+---->> phone line
| |
| o
| /
| / momentary switch
| |
| /
| \ 1200 Ohm
| /
-----____|
/ \
/___\ SCR
|
/
\ 600 Ohm
/
| ^^
----- //
/ \ //
/___\ LED
|
|
>>-----------------+--------->> phone line
4. Phone to audio interface (SSI202 input)


You have to isolate the chip from the phone line, or you'll have all kinds of problems. Let's see how I can do this with ascii art:

.22 uf 10k pot
400v ||(----------->
Phone line tip o-----)(----)||( <---o to SSI202 input
)||( >
Phone line ring o-----------)||(-----------o---o ground
The transformer is a 600-ohm to 600-ohm line transformer. I use the circuit as-is, and works fine. Doesn't take the phone off hook, you'll need to add some circuitry for that. To set the pot, turn it down all the way, (for minimum audio into the decoder) then hold down a tone on the phone while you slowly advance the pot up until the VALID DIGIT line changes on the chip. Then advance the pot a little past that point. That should do it. Also, it might not be a bad idea to put a couple of diodes back-to-back across the secondary of the transformer. I'm not sure if enough voltage will be generated to harm the SSI chip when the phone rings or not. Mine has never had a problem, but it might be worth the cost of the two diodes for good luck.

5. Phone Off-Hook Indicator

Author: Roger Petersen Created: June 1985 or so Overview - What is it? Runs off 9V battery, Plugs into phone jack, Lights an LED when any phone on the line is off-hook.
Phone Information
Measuring the voltage across the telephone line shows (typical numbers):

On Hook: 40 to 50 VDC
Off Hook: 4 to 6 VDC
Ringing: 100 VAC
The "standard" impedence of a telephone, when off-hook, is 680 ohms. Hanging a 680 ohm resistor across the telephone line will drop the voltage from 48V to about 5V, causing the line to go "active". This is how HOLD switches work. This probably means that it is bad to load down the phone line when the phone is off hook. I wouldn't want to hang less than a 100Kohm load across it. Should probably measure this, and see how it affects the on-hook voltage. I haven't seen any official documentation on these numbers. They're empirically derived.
The next question is: What are these voltages referenced to? If anything? It's possible that the most positive phone wire is tied to the GND in your house, or else maybe the neutral wire in your 120VAC outlet. So measuring the phone line voltages with respect to your household GND should show 0V and -48V when the phone is on-hook. But I don't know. It's probably best to not rely on this behavior.
Circuit Design - Off-hook Indicator
Could probably use some sort of transistor design, but I'm a digital weenie.
I used a CMOS 4049 Hex Interter. This part (supposedly) has high drive output. And since it's CMOS, it can operate with Vcc from +3 to +15V. And it has a high input impedence.

+9V
|
Phone+ -----+ |+
| LED
R 2.7Mohm |-
| |
| R 680 ohms
| 5 |\ 4 3 |\ 2 |
+-----------| >o------+-----| >o---------------+
| |/ 4049 | |/ 4049 |
| | |
| | |
R 0.56Mohm | 14 |\ 15 |
| +-----| >o---------------+
Phone- ------+ |/ 4049
|
|
GND

R = resistor. Those other things are inverters.
Connect 9V battery across +9V and GND, above.
Tie all unused inputs (pins 7,9,11) of the 4049 to GND! Don't let 'em float.
Tie Vcc (Pin 1) of 4049 to +9V
Tie GND (Pin 8) of 4049 to GND

Voltage going into pin 4 of 4049 is:
Phone voltage Voltage at pin 4
6V 1V
48V 8V
100V 16V
Fancy Features Not all phone jacks are wired the same way. Some have the two wires reversed. In the old days, before touch-tone, it didn't matter. In the early days of touch-tone, some phones didn't dial when the polarity was backwards. Now days, most phones don't care any more.
But the circuit above does. It requires the phone wires to be connected as shown. If you connect them backwards, it won't work. The light will just stay lit. And the 4049 may eventually be damaged. (4049's seem pretty resilliant). So it would be nice to have an easy way to switch the phone wires
Design Analysis
The 4049 probably takes a lot of abuse in this design. When the phone rings, the 4049 probably sees bursts of 16V. When the battery goes low, the voltage on pin 5 of the 4049 may exceed Vcc on the 4049, which is probably bad. It shouldn't be hard to improve on this circuit.

6. 'phone rang' indicator light


This, will detect the ring signal, energize the relay which latches up, and the LED comes on and stays on till you push SW.

____
tip o--CC---RR----o-----D<---o-----o------>D----^ ^----o-----+
| | | SW | |
| | | | |
\-/ |- R|| B- LED
Z C L|| ............ A |
| |+ Y|| __.__ T+ R
| | | +--o o---+ |
| | | | |
ring o------------o----------o-----o---------o----------------+

CC=.47 uF 200 V. capacitor
RR= 3k (depends on relay)
D = 200V diode ( < > direction od diodes)
Z = 12 zener
RLY= any small relay
SW= normally closed switch
K = relay's contacts
BAT= 9 V. battery
R = 500 ohm (for LED)
C = some (10) uF capacitor
Components are not critical. It should latch on first ring, if not reduce RR. If it took too long to deenergize, reduce the C.
7. Phone Line to Audio


We use telephone audio in our studio all the time. And yes, it's an off the shelf design. I designed and built such a device with scrap door components. I used an audio coupling transformer and a capacitor. The primary windings add in series to 500 ohms. Instead of connecting them directly together I added a cap between them. I think it was somthing like 0.047 micro farads with a 600vlt rating. And the secondary which is 500 ohms runs into the control room mixer.

Tip >------------/ II
/ II /------------<
(primary winding 1) / II /
/ II /
>-----X------/ II /
I II /
0.047 uF = II / -----------CT (secondary winding)
I II /
>------X------/ II / Output Side
/ II / to Mixer
(primary winding 2) / II /
/ II /-------------<
Ring >-------------/ II
Try this circuit it works great for us in the studio. Just make sure you use properly rated components.
8. Phone in-use


The circuit I built gives a visual indication at each extension when any extension is off-hook. It is line-powered, and the maximum number that can be used on our system is three. Since they all draw power at the same time to light the LEDs, any more indicators would cause an off-hook condition. Some changes could be made to reduce the current draw, to allow using more indicators, but the brightness of each led would suffer. The LEDs I used are tiny, but amazingly bright on just a couple milliamps. I picked them up from a surplus catalog, I can't remember which one. If you were to use battery power for the circuit, you could use almost any number of indicators. I had use only for three, and I did not want to worry about replacing batteries. If I remember correctly, our pbx required a load of about 20 milliamps before the line failed to hang up. This circuit draws about 5 milliamps when off- hook, much less when on-hook. It senses the drop in line voltage from about 46 volts to 6 volts when an extension is picked up. The zener voltage should be well above the off-hook voltage of your system, and well below the on-hook voltage. The transistors are small high-voltage npn types I had on hand. The LED also flashes with the ring voltage. Putting a suitable MOV across the line is a good precaution to prevent lightning damage.

(+)------------+---------------+--------------------------+
green | | |
/ / /
\ 2200 \ 100K 100K \
/ / /
1N4148 \ \ \
+---------+ | |
___|___ ___|___ | ___|___/
/ \ \ / LED | 10V / / \
/_____\ __\ /__ | ZENER /_____\
| | | |
+---------+ | |
| c | |
\ | | |
MPSA42 \|-----------+------------- c |
/| ___|___ \ | |
/ | / \ MPSA42 \|--------+
| e /_____\ /| ___|___
| 1N4148 | / | / \
| | | e /_____\
| | | |
(-)------------+---------------+-------------+------------+
red 1N4148
9. Telephone Line Monitor (Plans)


Get yourself a low-voltage DC relay, like a 3v relay... Set it up as follows:

Audio Isolation
Transformer
To <--)||(---------------------+
)||( | <==== Relay Contacts
Speaker <--)||(---+ +--------o/ o
600ohm | | mmmmm DC 3v Relay Coil
| | | |
RED -----------|----+-------+ +----------> To Dispatcher's Phone
|
GREEN -----------+-----------------------------> To Dispatcher's Phone

| |
-+- indicates a connection, --- is not connected.
| |
You may have to use a Diode or two to make this telephone-line FCC clean... I'm not saying this is a clean circuit at all. It's cheap and dirty! You may have to use a Op-Amp (Use an LM386, they're good for speakers) on the speaker. Depends. Experiment! Circuit Theory:
When the Dispatcher picks up the phone (in a standard circuit, I have NO clue what your PBX does.. this will work on standard home phones, and I used to use it for a tape-recording controller) Hey, there's an Idea - spend $25 on a telephone recording device, and hitch it to a nice loud amp and speaker combo, instead of a tape deck. It'll save you loads of time...
Anyhow.. the voltage will turn into DC, approx 6-10VDC when the phone is picked up, (which is why you've gotta put it before the dispatcher's phone) and click the relay. The relay will connect the transformer, and feed the speaker. it might be towards your advantage to use a SPDT relay, and connect BOTH ends of the transformer, and not just switch one end in and out. That might prevent some line noise...

10. Use old phones as an intercom


I have recently thought about this and come up with a kludgy but workable scheme.
Talking over the phones is easy. You put DC current through the phone and it transmits and receives audio. So two phones and a current source (about 25mA) all in series will give you a talking circuit. A suitable current source can be as simple as a 9V battery and a series resistor whose value is adjusted (with both phones offhook) till about 25mA flows. You can then bypass the battery and the resistor with a capacitor to couple the audio straight across and get a loud and clear connection.
What is much harder is signaling the other end. To ring the bell you need to put 90V (RMS) 20Hz AC into the phone (nominally). Lower voltages will work (down to about 40V) but different frequencies won't. You can't ring the phone at 60Hz. I have a ringing circuit in a PBX I built but it consists of a 20Hz sinewave generator, a push-pull power booster and a big transformer. Much too elaborate for a simple 2-phone intercom circuit, and anyway the ringing voltage could painfully zap a kid.
So forget the bell and look into other forms of signaling. This is what I have come up with:

+ | | -
+-------+------ - - --+---||||---/\/\/--+---- - -----+-------+
| | | | | R | | |
| | | 24V | | |
| --- | | --- |
| | | +---||------------+ | | |
| --- Sonalert C Sonalert --- |
| C | | C |
+---||--+ +--||---+
| _|_, _|_ |
| / \ 15V 15V \ / |
PHONE -+- Zener Zener `-+- PHONE
| | | |
| | | |
+-------+------------------ - - - -------------------+-------+
As before, set R to give you a talking current (both phones offhook) of about 25mA. Start with 1K ohm. Leave it in if the phones work well enough; the current is not very critical. The capacitors C are audio bypass capacitors and should be about 0.47uF. When the phones are onhook they present an open circuit, and the 24V battery voltage is not enough to overcome the 30V series drop of the Zeners and no current flows. When both phones are offhook they present a very low resistance and the talking current (determined by R) flows.
When only one phone is offhook it places its low DC resistance across the Zener diode on its side so that the full 24V supply is applied to the other side. This overcomes the voltage drop of the other Zener diode so the other Sonalert beeps. The wonderful thing about Sonalerts is that they make a loud noise with only a few milliamps of current so the series resistor R doesn't matter. Especially nice is a pulsing Sonalert which goes "Beep beep beep" automatically. While the far-end Sonalert is beeping, you hear the beeping in the near-end receiver (at low volume thanks to the bypass capacitor across the far-end Sonalert) to confirm that the line is working and the other end is being signaled.
The power supply can be three 9V batteries in series but since 80% of the power is lost in series resistor R rather than in powering the phones it seems a little wasteful. A 24V wall wart with clean filtering would be better.
The signaling components can be mounted inside the phones. Only two wires are needed to go to each phone, and the power supply can be mounted centrally, out of harm's way. If R is adequately big (1/2 watt) and has enough ventilation then both lines can be indefinitely shorted out without any fire hazard and there is not enough voltage anywhere to hurt anyone.
I have tested this with 500-type phones and two different types of piezo buzzers (pulsing sonalerts and non-pulsing brand X ones) and it works great. You should be able to get all the needed parts including piezo buzzers at Radio Shack. I love telephones. Too bad I don't have any kids who want an intercom line.

11. Phone-In-Use indicator



------+-------------+-------------+----------- pos (tip)
| | |
| | ---
| | R3 | |
| | | |
| | ---
zener | | |
/------/ --- -----
/ \ R2 | | \ / LED
------ | | -----
| --- |
| | |
| --------+----+ ---+
| |/ | |/
+---| npn1 +---| npn2
| |\ |\
--- -+ -+
R1 | | | |
| | | |
--- | |
| | |
------+------+------------------+-------------- neg (ring)
Now here's some logic that should work fine with the right zener and the right resistors and a couple of cheap npn's 2n2222A's or 2n3904's (06's?). If you get close to 25 volts with the new smart test boxes, a 20 volt Z may work fine. Choose R1 to limit current through Z and have enough left to turn on npn1 just enough to deprive npn2, choose R2 for that, and you will need to add a resistor R3 to protect the LED from overcurrent as needed, depending on the phone system you have! You MIGHT need a resistor between the bottom of R2 and the base of npn2 to get it right, but I don't think so because of the B-E 0.7 volt diode junction voltage needed in npn2 to get it out of cutoff.

12. Telephone Power?



" If one were to try [using power from phone line], would phone company had a way of finding out?"
Most assuredly. They aren't in the business of supplying power, and they ARE in the business of finding faults in their lines. Any substantial power drain from their lines WILL be detected. If it's large, the phone switch will conclude that you've dropped the phone in the bathtub or something like that, and will disconnect your line (and will check periodically to see if the drain has gone away and you can be reconnected). If it's small, the switch will report it to the service people as a possible line problem, to be investigated before it causes a complete failure... and if they investigate and find that you're to blame, they will probably send you a bill for time and trouble. The current you can draw without eventually having it noticed is very small.
13. Hold function for Telephone


Here's the schematic that was in the November 1992 issue of Electronics Now. (Nobody sue me)

+-------+------+ R1 = 2.2K
| | | R2 = 1 K
-| SW R | R3 = 47 ohms
| 1 | SCR = 2N5064, TIC47, or MCR104
| | |
R LED | Well, that's it, just remember that
2 | | the cathode of both the SCR and the
| | +----- RING (Red) LED are towards the bottom.
+------SCR
| | +----- TIP (Green)
R | |
3 | |
| | |
+-------+------+
14. Digital/Standard Phone Line Tester


Radio Shack sells a similar device without the high current function. It detects one or two lines on an RJ-11 and tells you its polarity. It costs $6. The schematic is:
o-------+----------+
| |
\ |
Line 1 /680 \ / red/green LED
\ .5W ---
| |
o-------+----------+
The circuit for Line 2 is identical. Note that each red/green LED comes standard as reverse wired (red LED "forward", green LED "reversed). Based on the above, I think an appropriate modification to include a high current indicator would be: (I've tested it)

20
o--+-\/\/\/--+-----------+----------+
| | | |
| | \ ---
+--->|----+ / / \ red/green LED
red/green \ 680 |
LED | .5W |
o------------------------+----------+
You can adjust the 20ohm resistor value to set what is considered "high current". 20ohms lights the LED at around 90ma. Total parts costs under $4, or if you use Radio Shack's $6 line tester and add the above resistor and LED, then under $7. (I'm not faulting IBM for charging $30). This whole issue really bothers me because it means that I can't bring a PCMCIA modem with me on trips and count on it working at any given hotel. That means I should carry around my pocket modem just in case. So then what's the point of having the PCMCIA modem!
​

 

1.5 volt dual LED flasher (runs one year)

This 1.5 volt led fasher runs more than a year on a single 'd" cell and alternately flashes 2 LEDs at about a 1 second rate. The circuit employs a 74HC14 CMOS hex inverter that will operate at very low voltages (less than 1 volt). One section is used as a squarewave oscillator (pins 1 and 2), while the others are wired to produce a short 10mS pulse on alternate edges of the square wave so the LEDs will alternate back and forth. The output sections each use a capacitor charge pump to increase the voltage for the LEDs. The circuit draws an average current of 800uA from the 'D' battery and the LED peak current is about 40mA with a fresh battery and drops to about 10mA as the battery voltage falls to 1.1 volts. The capacity of a alkaline 'D' cell is about 12 amp hours with a cutoff voltage of 1.1 so the circuit should run about 12/.0008 = 15000 hours or maybe 625 days, but I haven't verified that yet. The idea for this circuit came from a single 1.5 volt LED flasher by Dave Johnson that can viewed at


Descrete Multistage Light Sequencer

The drawing below illustrates a multistage light sequencer using descrete parts and no integrated circuits. The idea is not new and I hear a similar circuit was developed about 40 years ago using germanium transistors. The idea is to connect the lights so that as one turns off it causes the next to turn on, and so forth. This is accomplished with a large capacitor between each stage that charges when a stage turns off and supplies base current to the next transistor, thus turning it on. Any number of stages can be used and the drawing below illustrates 3 small Christmas lights running at about 5 volts and 200mA. The circuit may need to be manually started when power is applied. To start it, connect a momentary short across any one of the capacitors and then remove the short. You could use a manual push button to do this.
Detailed operation:
Assume the circuit doesn't start when power is applied amd all lights are off and all three capacitors are charged to about 5 volts. We connect a jumper across the 220uF capacitor on the left which discharges the capacitor and turns on the 2nd stage transistor and corresponding light. When the jumper is removed, the capacitor will start charging through the base of the stage 2 transistor and stage 1 light. This causes the stage 2 transistor to remain on while the capacitor continues to charge. At the same time, the capacitor connecting stage 2 and 3 will discharge through the 100 ohm resistor and diode and stage 2 transistor. When the capacitor charging current falls below what is needed to keep stage 2 turned on, the transistor and light will turn off causing the voltage at the collector of the stage 2 transistor to rise to 5 volts. Since the capacitor connecting stage 2 and 3 has discharged and the voltage rises at the collector of stage 2, the capacitor from stage 2 and 3 will charge causing the 3rd stage to turn on and the cycle repeats for sucessive stages 4,5,6,7.... and back to 1. The sequence rate is determined by the capacitor and resistor values (220uF and 100 ohms in this case), load current (200mA in this case), and current gain of the particular transistor used. This arrangement runs at about 120 complete cycles per minute for 3 lights, or about 167mS per light. Faster or slower rates can be obtained with different capacitor values.
16 Stage Bi-Directional LED Sequencer

The bi-directional sequencer uses a 4 bit binary up/down counter (CD4516) and two "1 of 8 line decoders" (74HC138 or 74HCT138) to generate the popular "Night Rider" display. A Schmitt Trigger oscillator provides the clock signal for the counter and the rate can be adjusted with the 500K pot. Two additional Schmitt Trigger inverters are used as a SET/RESET latch to control the counting direction (up or down). Be sure to use the 74HC14 and not the 74HCT14, the 74HCT14 may not work due to the low TTL input trigger level. When the highest count is reached (1111) the low output at pin 7 sets the latch so that the UP/DOWN input to the counter goes low and causes the counter to begin decrementing. When the lowest count is reached (0000) the latch is reset (high) so that the counter will begin incrementing on the next rising clock edge. The three lowest counter bits (Q0, Q1, Q2) are connected to both decoders in parallel and the highest bit Q3 is used to select the appropriate decoder. The circuit can be used to drive 12 volt/25 watt lamps with the addition of two transistors per lamp as shown below in the section below titled "Interfacing 5 volt CMOS to 12 volt loads"

Interfacing 5 volt CMOS to 12 volt/ 25 Watt Loads

The circuit below is designed to be used with the bi-directional lamp sequencer shown above on this same page. Two additional transistors are used to increase the current from the 74HCT138 decoder to control 12 volt 25 watt lamps. A 6.8 volt/1 watt zener diode is used in series with the ground connection of all the CMOS ICs (74HC14, CD4516 and 74HC138s) so that the total voltage across the CMOS devices will be about 5.2 volts and the outputs will move from +12 to about +7 when selected. The 2N2905/PNP transistor stage is connected as an emitter follower which provides a high impedance to the decoder output and supplies about 80 mA of current to the base of the 2N3055 NPN power transistor which then supplies 2 or more amps to the 12 volt lamp. The voltage across the PNP transistor will be about 7 volts when it is turned on and the heat dissapation will be about 0.6 watts. That should't require a heat sink if several lamps are sequencing but it may get quite warm if the circuit is idle on a single output. The 2N3055 power transistor operates as a switch and drops very little voltage (less than 0.5) when conducting, and will not require a heat sink. Other transistors may be substituted such as the TIP29 or TIP31 for the 2N3055 and most any medium power (500mA) PNP for the 2N2905.
Expandable 16 Stage LED Sequencer

The circuit below uses a hex Schmitt Trigger inverter (74HC14) and two 8 bit Serial-In/Parallel-Out shift registers (74HCT164 or 74HC164) to sequence 16 LEDs. The circuit can be expanded to greater lengths by cascading additional shift registers and connecting the 8th output (pin 13) to the data input (pin 1) of the succeeding stage. A Schmitt trigger oscillator (74HC14 pin 1 and 2) produces the clock signal for the shift registers, the rate being approximately 1/RC. Two additional Schmitt Trigger stages are used to reset and load the registers when power is turned on. Timing is not critical, however the output at pin 8 of the Schmitt Trigger must remain high during the first LOW to HIGH clock transition at pin 8 of the registers, and must return low before the second rising edge to load a single bit. If the clock rate is increased, the length of the signal at pin 9 of the Schmitt Trigger should be reduced proportionally to avoid loading more than one bit. The HCT devices will normally provide about 4 mA (source or sink) from each output but can supply greater currents (possibly 25 mA) if only one output is loaded. The common 150 ohm resistor restricts the current below 25 mA using a 6 volt power source. If the circuit is operated with two or more LEDs on at the same time, resistors may be needed in series with each LED to avoid exceeding the maximum total output current for each IC of 25 mA. For greater brightness, individual buffer transistors can be used as shown in the 10 stage LED sequencer on this same page.

10 Channel LED Sequencer

18 Stage LED Sequencer


The question sometimes comes up of how to cascade 4017 decade counters for more than 10 sequencial stages. The LED sequencer below shows a possible solution using a few extra parts. When power is applied, the 15K resistor and 10uF cap at pin 15 will reset the counters to the zero count where pin 3 is at +12 and all other outputs are at zero. The 2 diodes (1n914) and 15 resistor form a AND gate so the clock pulse will be passed to the right side counter when the sequence starts. When the right counter reaches the 10th count, pin 11 will move high enabling the AND gate on the right to pass the clock pulse to the left side counter. As the left side counter advances, pin 3 will be low so that clock pulses cannot advance the right counter. When the left counter turns over and pin 3 again moves high, the sequence will repeat. Thus we get 18 total counts, 9 from the first counter, and 9 from the second.
Note that the 4017 counter will not deliver much current, and so the LED current is set to about 6mA using a 1.5K resistor in series. For more current, you could use transistors on each output as shown in the drawing above, (10 Channel LED Sequencer). But some of the newer bright LEDs are fairly bright at 6mA.

Two Transistor LED Flasher

Fading Red Eyes


Circuit description:

This circuit is used to slowly illuminate and fade a pair of red
LEDs (light emitting diodes). The fading LEDs could be installed
as 'eyes' in a small pumpkin or skull as a Halloween attraction,
or mounted in a Christmas tree ornament. Or, they might be used
as a fancy power indicator for your computer, microwave oven,
stereo system, TV, or other appliance.

In operation, a linear 3 volt (peak to peak) ramping waveform is
generated at pin 1 of the LM1458 IC and buffered with an emitter follower
transistor stage. The 22uF capacitor and 47K resistor connected to
pin 2 establish the frequency which is about 0.5 Hz. You can make the
rate adjustable by using a 100K potentiometer in place of the 47K
resistor at pin 2.

The circuit consists of two operational amplifiers (opamps),
one producing a slow rising and falling voltage from about 3 volts to
6 volts, and the other (on the right) is used as a voltage comparator,
the output of which supplies a alternating voltage switching between
2 and 7 volts to charge and discharge the capacitor with a constant
current.

Each of the op-amps has one of the inputs (pins 3 and 6) tied to a
fixed voltage established by two 47K resistors so that the reference
is half the supply voltage or 4.5 volts. The left opamp is connected
as an inverting amplifier with a capacitor placed between the output
(pin 1) and the inverting input (pin 2). The right opamp is connected
as a voltage comparator so that the output on pin 7 will be low when
the input is below the reference and high when the input is higher
than the reference. A 100K resistor is connected between the comparator
output and input to provide positive feedback and pulls the input
above or below the switching point when the threshold is reached.
When the comparator output changes at pin 7, the direction of the
current changes through the capacitor which in turn causes the inverting
opamp to move in the opposite direction. This yields a linear ramping
waveform or triangle waveform at pin 1 of the inverting opamp.
It is always moving slowly up or down, so that the voltage on the
non-inverting input stays constant at 4.5 volts.

Adjustments to the point where the LEDs extinguish can be made
by altering the resistor value at pin 3 and 6 to ground. I found
a 56K in place of the 47k shown worked a little better with the
particular LEDs used. You can experiment with this value to get
the desired effect.


Parts List:

Description Mfg Part# Allied Part# Quantity Cost

Operational Amplifier LM1458 288-1090 1 .48
47K Resistor 296-2182 4 .42
100K Resistor 296-5610 1
100 Ohm Resistor 895-0465 1 .24
Transistor 2N3904 568-8253 1 .1
22uF Capacitor 852-6516 1 .07
Solderless Breadboard 237-0015 1 6.99
Red Light Emitting Diode (LED) 670-1224 2 0.50

Note: The LED listed has a narrow viewing angle of 30 degrees and
appears brightest when looking directly at it. It's not a pure red
color, and a little on the orange side, but should be brighter
compared to other selections. For a wider viewing angle at reduced
intensity, try part number 670-1257 which is viewable at 60 degrees
and has a red diffused lens.

Construction details:

Layout of the solderless breadboard:

Refer to the drawing below the schematic diagram and note the
solderless breadboard is arranged in rows labeled A-J, and
columns numbered 1 to 65. Each group of 5 holes in the same column
are the same connection, so that holes A1,B1,C1,D1 and E1 are all
connected together. Likewise holes F1,G1,H1,I1 and J1 are all
the same connection. The outer rows along the length of the
board are also connected together and are normally used for
power supply connections. However, there is a break in the
mid section of the outer rows, so a short jumper wire connecting
the mid section of the outer rows should be installed to connect
the entire outer row together. If you have a DMM, use the low
ohms range and probe the various holes to get familiar with the
board layout.

Installing the components:

Orientate the LM1458 so the nook or punch mark on one edge
is near column 30 and the opposite edge is near column 33.
Install the LM1458 on the breadboard so the pins straddle
the center section of the board and pin 1 of the IC is occupying
hole F30 and pin 8 is in hole E30. The pins are numbered counter
clockwise, so pin 4 will be occupying F33 and pin 5 will be in E33.
Possible connections for the LM1458, 9 volt battery, and a couple
other parts is illustrated in the lower drawing of the solderless
breadboard, but it is not complete with all parts.

Refer to the schematic diagram, and install the various other
components so they connect to the appropriate pins of the
LM1458. Use whatever connection holes are convenient.
For example, the 22uF capacitor connects between pins 1 and 2
of the IC, which occupy holes (F30,F31) so it could be placed
in the holes (H30, H31) or (J30,J31) or (I30,I31). But not all parts
will conveniently fit, so you may have to use a short jumper
wire (#22 preferred) to connect parts from one side of the chip
to the other.

The board I assembled was connected this way:

LM1458 F30 to F33, and E30 to E33
22uF capacitor H30 to H31
47K resistor I30 to I35
47K resistor C27 to C31
47K resistor F25 to Positive battery row
47K resistor J25 to Negative Battery row
100K resistor B31 to B33
2N3904 Transistor G36, G37, G38 with emitter at G38
100 Ohm resistor D38 to F38
LED B43 to B44 (Cathode at B44)
LED I43 to I44 (Cathode at I43)
Jumper A30 to Positive battery row
Jumper F36 to Positive battery row
Jumper J33 to Negative battery row
Jumper J43 to Negative battery row
Jumper H25 to J32
Jumper J30 to J37
Jumper E27 to G31
Jumper D32 to G32
Jumper D33 to H35
Jumper C38 to C43
Jumper E44 to F44
9 Volt Battery Postive battery row to negative row.

The circuit below illustrates two pairs of LEDs that operate out of phase so as one pair slowly illuminate, the other pair will fade. Automobile Interior Lights Fader


This circuit is similar to the fading eyes circuit above and is used to slowly brighten and fade interior lights of older cars. The circuit is based around the LM324 low power opamp which draws around 3mA of current, so it won't bother the battery if left connected for extended periods.
The top two opamps (pins 1,2,3 and 5,6,7) form a triangle wave oscillator running at about 700Hz while the lower opamp (pins 8,9,10) produces a linear, 5 second ramp, that moves up or down depending on the position of the door switch. The two transistors and associated resistors serve to limit the ramp voltage to slightly more and less than the upper and lower limits of the triangle waveform. These two signals (700 hZ. triangle wave and 5 second ramp) are applied to the inputs of the 4th opamp (pins 12,13,14) that serves as a voltage comparator and generates a varying duty cycle square wave that controls the IRFZ44 MOSFET and lamp brightness. The 5 second fade time can be adjusted with the 75K resistor connected to the door switch. A larger value will increase the time and a smaller value will speed it up.
When the door switch is closed (car door open) the voltage on pin 8 slowly rises above the negative peaks of the triangle wave producing a short duty cycle output and a dim light. As the ramp moves farther positive, a greater percentage of the triangle wave will be lower than the ramp voltage producing a wider pulse and brighter light. This process continues until the ramp is 100% above the positive peaks of the triangle wave and the output is maximum. When the door switch is open, the reverse action takes place and the lamps slowly fade out.
The IRFZ44 shouldn't require a heat sink if the total load is 50 watts or less but the temperature of the MOSFET should be monitored to insure it doesn't overheat. The on-state resistance is only 0.028 ohms so that 4 amps of current (48 watts) is only around 100mW. For larger loads, a small heat sink can be added to keep the MOSFET cool.

28 LED Clock Timer


This is a programmable clock timer circuit that uses individual LEDs to indicate hours and minutes. 12 LEDs can be arranged in a circle to represent the 12 hours of a clock face and an additional 12 LEDs can be arranged in an outer circle to indicate 5 minute intervals within the hour. 4 additional LEDs are used to indicate 1 to 4 minutes of time within each 5 minute interval.

The circuit is powered from a small 12.6 volt center tapped line transformer and the 60 cycle line frequency is used for the time base. The transformer is connected in a full wave, center tapped configuration which produces about 8.5 volts unregulated DC. A 47 ohm resistor and 5.1 volt, 1 watt zener regulate the supply for the 74HCT circuits.

A 14 stage 74HCT4020 binary counter and two NAND gates are used to divide the line frequency by 3600 producing a one minute pulse which is used to reset the counter and advance the 4017 decade counter. The decade counter counts the minutes from 0 to 4 and resets on the fifth count or every 5 minutes which advances one section of a dual 4 bit binary counter (74HCT393). The 4 bits of this counter are then decoded into one of 12 outputs by two 74HCT138 (3 line to 8 line) decoder circuits. The most significant bit is used in conjunction with an inverter to select the appropriate decoder. During the first eight counts, the low state of the MSB is inverted to supply a high level to enable the decoder that drives the first 8 LEDs. During counts 9 to 12, the MSB will be high and will select the decoder that drives the remaining 4 LEDs while disabling the other decoder. The decoded outputs are low when selected and the 12 LEDs are connected common anode with a 330 ohm current limiting resistor to the +5 volt supply. The 5th output of the second decoder (pin 11) is used to reset the binary counter so that it counts to 11 and then resets to zero on the 12th count. A high reset level is required for the 393 counters, so the low output from the last decoder stage (pin 11) is inverted with one section of a 74HCT14 hex Schmitt trigger inverter circuit. A 10K resistor and 0.1uF cap are used to extend the reset time, ensuring the counter receives a reset signal which is much longer than the minimum time required. The reset signal is also connected to the clock input (pin 13) of the second 4 bit counter (1/2 74HCT393) which advances the hour LEDs and resets on the 12th hour in a similar manner.

Setting the correct time is accomplished with two manual push buttons which feed the Q4 stage (pin 7) of the 4020 counter to the minute and hour reset circuits which advance the counters at 3.75 counts per second. A slower rate can be obtained by using the Q5 or Q6 stages. For test purposes, you can use Q1 (pin 9) which will advance the minutes at 30 per second.

The time interval circuit (shown below the clock) consists of a SET/RESET flipflop made from the two remaining NAND gates (74HCT00). The desired time interval is programmed by connecting the anodes of the six diodes labeled start, stop and AM/PM to the appropriate decoder outputs. For example, to turn the relay on at 7:05AM and turn it off at 8:05AM, you would connect one of the diodes from the start section to the cathode of the LED that represents 7 hours, the second diode to the LED cathode that represents 5 minutes and the third diode to the AM line of the CD4013. The stop time is programmed in the same manner. Two additional push buttons are used to manually open and close the relay. The low start and stop signals at the common cathode connections are capacitively coupled to the NAND gates so that the manual push buttons can override the 5 minute time duration. That way, you can immediately reset the relay without waiting 5 minutes for the start signal to go away.

The two power supply rectifier diodes are 1N400X variety and the switching diodes are 1N914 or 4148s but any general purpose diodes can be used. 0.1 uF caps (not shown on schematic) may be needed near the power pins of each IC. All parts should be available from Radio Shack with the exception of the 74HCT4017 decade counter which I didn't see listed. You can use either 74HC or 74HCT parts, the only difference between the two is that the input switching levels of the HCT devices are compatible with worst case TTL logic outputs. The HC device inputs are set at 50% of Vcc, so they may not work when driven from marginal TTL logic outputs. You can use a regular 4017 in place of the 74HCT4017 but the output current will much lower (less than 1 mA) and 4 additional transistors will be required to drive the LEDs. Without the buffer transistors, you can use a 10K resistor in place of the 330 and the LEDs will be visible, but very dim. Using the 4017 to drive LEDs with transistor buffers is shown in the "10 Channel LED Sequencer" at the top of this page.
Time Interval Relay Circuit
for the clock circuit above

72 LED Clock

In the circuit below, 60 individual LEDs are used to indicate the minutes of a clock and 12 LEDs indicate hours. The power supply and time base circuitry is the same as described in the 28 LED clock circuit above. The minutes section of the clock is comprised of eight 74HCT164 shift registers cascaded so that a single bit can be recirculated through the 60 stages indicating the appropriate minute of the hour. Only two of the minutes shift registers are shown connected to 16 LEDs. Pin 13 of each register connects to pin 1 of the next for 7 registers. Pin 6 of the 8th register should connect back to pin 1 of the first register using the 47K resistor. Pins 2,9,8, 14 and 7 of all 8 minutes registers (74HC164) should be connected in parallel (pin 8 to pin 8, pin 9 to pin 9, etc.). The hours section contains two 8 bit shift registers and works the same way as the minutes to display 1 of 12 hours. Pin 9 of all 74HCT164s (hours and minutes) should be connected together. For 50 Hertz operation, the time base section of the circuit can be modified as shown in the lower drawing labeled "50 Hertz LED Clock Time Base". You will need an extra IC (74HC30) to do this since it requires decoding 7 bits of the counter instead of 4. The two dual input NAND gates (1/2 74HC00) that are not used in the 50 Hertz modification should have their inputs connected to ground.
When power is applied, a single "1" bit is loaded into the first stage of both the minutes and hours registers. To accomplish this, a momentary low reset signal is sent to all the registers (at pin 9) and also a NAND gate to lock out any clock transitions at pin 8 of the minutes registers. At the same time, a high level is applied to the data input lines of both minutes and hours registers at pin 1. A single positive going clock pulse (at pin 8) is generated at the end of the reset signal which loads a high level into the first stage of the minutes register. The rising edge of first stage output at pin 3 advances the hours (at pin 8) and a single bit is also loaded into the hours register. Power should remain off for about 3 seconds or more before being re-applied to allow the filter and timing capacitors to discharge. A 1K bleeder resistor is used across the 1000uF filter capacitor to discharge it in about 3 seconds. The timing diagram illustrates the power-on sequence where T1 is the time power is applied and beginning of the reset signal, T2 is the end of the reset signal, T3 is the clock signal to move a high level at pin 1 into the first register, T4 is the end of the data signal. The time delay from T2 to T3 is exaggerated in the drawing and is actually a very short time of just the propagation delay through the inverter and gate.
Two momentary push buttons can be used to set the correct time. The button labeled "M" will increment the minutes slowly and the one labled "H" much faster so that the hours increment slowly. The hours should be set first, followed by minutes.

50 Hertz LED Clock Timebase

60 Light Sequencer using a Matrix

The circuit below illustrates using a 10x10 matrix to sequence up to 100 LEDs with just three ICs and 20 transistors. The two 4017 decade counters control the 10 rows and 10 columns so that one LED is selected depending on the output of the decade counters.
The LED circuit is drawn showing 25 LEDs and 10 transistors but can be expanded up to a 100 by using sucessive stages of the 4017 counters.
For example, to expand the circuit to 60 LEDs for displaying minutes or seconds of a clock, the rows counter could be reset from pin 12 (carry out) rather than pin 1 as shown, and the columns counter will be reset from pin 5 rather than pin 1 as shown. And then add transistors to pins 1,5,6,9,and 11 of the rows counter and pin 1 of the columns counter. Take a look at the "10 Stage LED Sequencer" for a listing of all the connections of the 4017 decade counter.


25 Light Sequencer using Xmas lamps

This circuit is same as the above setup to drive 25 small Xmas lights. The lights operate at about 200mA and 3 volts. The supply voltage is set to 5 volts and the 4017 counter output will drop about a volt using the 2N3053 transistors. The voltage on the emitters of the rows transistors will be about 0.7 volts less than the base so the lamp voltage will be about 3 volts. You can adjust the supply voltage for the desired current if necessary. It works the same way as the LED version but you need diodes in series with each light. Most any small diode rated at 500mA or more should work. I used 1N4001 diodes. Various NPN transistors can be used, I tried 2N2219A and 2N3053. The 2N3053 worked out better with a higher gain than the 2N2219A, but either one should work.

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Mixed-Signal And DSP Design Technique (Analog Devices Series)

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Practical Design Techniques For Sensor Signal Conditioning (Analog Devices Series)


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