محتاج كتلوك دوائر الكترونيه

المصدر: محتاج كتلوك دوائر الكترونيه
في منتدى : قسم الفيزياء

السلام عليكم
الي عندة كتلوك او تجارب في الالكترونيك او كتاب يرسلياه
حتى لو يرسلة على الاميل
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يمنع وضع الايميلات في المشاركات
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العناصر الرمز
الوظيفة سلك Wire لتمرير التيار الكهربائي من نقطة الى اخرى نقاط لحام

اسلاك غير متصله

خلية Cell عدت خلايا تشكل ما يعرف بالبطارية بطارية Battery البطارية الكهربائية هي العنصر المسؤل عن امداد الدوائر الالكترونية بالكهرباء
مصدر مستمر DC مصدر متردد AC فاصلة Fuse حماية الدوائر الكهربائية محول كهربائي Transformer في الغالب يستخدم لرفع او تقليل الجهد الكهربائي
تأريض Earth
(Ground) التأريض مهم لحماية الاجهزة الكهربائية , في الدوائر الالكترونية يستخدم هذا الرمز ليدل على 0 فولت او الطرف السالب مصباح Lamp مؤشر مصباح

سخان كهربائي Heater رمز السخان الكهربائي المستخدم في الافران وبعض الاجهزة الصناعية والمنزلية محركMotor
جرس

جرس صغير Buzzer
ملف Coil يقوم الملف بتوليد مجال مغناطيسي بمجردد مرور التيار الكهربائي فيه مفتاح ضاغط Push Button فتح وغلق الدوائر الكهربائية
هذا المفتاح يغلق فقط عن الضغط عليه ويبقى مفتوح عند تركه مفتاح ضاغط
هذا المفتاح يفتح فقط عن الضغط عليه ويبقى مغلق عند تركه مفتاح تشغيل واطفاء 2-way Switch مفتاح للتشغيل والاطفاء مفتاح مساريين SPDT مفتاح كهربائية له مساريين مفتاح مزدوج Dual On-Off Switch
(DPST) مفتاح للتشغيل والاطفاء مزدوج
يعمل كلا المفتاحيين في نفس الوقت بمجرد الضغط مفتاح مزدوج بمساريين
DPDT مفتاح له مساريين
يعمل كلا المساريين في نفس الوقت بمجرد الضغط على المفتاح حاكمة Relay لتشغيل واطفاء الاجهزة مقاومة Resistor المقاومة هي عنصر يقاوم تدفق التيار الكهربائي في الدائرة مقاومة متغييرة بطرفيين (Rheostat) مقاومة يمكن تغيير قيمتها مقاومة متغييرة بثلاثة اطراف (Potentiometer) مقاومة تقسم الجهد مقاومة متغييرة دقيقة (Preset) مقاومة دقيقة في الغالب تستخدم داخل الجهاز لمعايرة الدائرة الالكترونية مكثف Capacitor مكثف التحكم في تدفق للشحنة الكهربائية في الدائرة الالكترونية . مكثف قطبي Capacitor, polarised يثبت هذا النوع من المكثفات بحسب قطبية اطرافه
مكثف متغيير Variable Capacitor مكثف تضبط قيمته
مكثف ضبط دقيق Trimmer Capacitor لضبط ومعايرة اجهزة اللاسلكي ثنائي - دايود Diode ثنائي ضوئي LED
Light Emitting Diode ثنائي زنر Zener Diode ثنائي يعمل بأنحياز عكسي عن جهد محدد ثنائي مستقبل للضوء Photodiode ثنائي يعمل عند تسليط الضوء عليه الثايرستور thyristor - SCR ثنائي يعمل عند تسليط نبضة على قاعدته
الداياك Diac عنصر ثنائى الاتجاه يمكنه التحول من حالة القطع الى حالة التوصيل الترياك Triac عنصر يتعامل مع التيار المتردد السيداك SIDAC عنصر شبه موصل ينتمي لعائلة الثايرستور ترانزيستور Transistor NPN ترانزيستور Transistor PNP ترنزيستور ضوئي Phototransistor ترانزيستور يعمل عند تسليط الضوء على القاعدة كريستال
كوارتز Crystal مايك Microphone عنصر يحول اهتزاز الصوت الى اشارة كهربائية سماعة أذن Earphone عنصر يحول الاشارة الكهربائية الى اهتزازات صوتية سماعة كبيرة Speaker عنصر يحول الاشارة الكهربائية الى اهتزازات صوتية مكبر أشارة Amplifier عنصر يقوم بتضخيم الاشارة الكهربائية هوائي Aerial
(Antenna) استقبال الأشارات اللاسلكية مقياس جهد Voltmeter قياس فرق الجهد بين نقطتين ويأتي بنوعين رقمي وتماثلي مقياس تيار Ammeter قياس قيمة سريات التيار ويأتي بنوعين رقمي وتماثلي
Galvanometer مقياس تيار دقيق يستطيع قياس التيارات الصغيرة جدا مقياس مقاومة Ohmmeter
جهاز اوسليسكوب Oscilloscope احدى الاجهزة الاحترافية التى يستخدمها فني الالكترونيات مصدر تغذية مستمر

مصدر تغذية متردد

مقاومة ضوئية LDR مقاومة تقل قيمتها كلما زادت قوة الضوء المسلط عليها مقاومة حرارية Thermistor مقاومة تتأثر قيمتها بشكل كبير مع تغير درجة الحرارة الفاريستور Varistor عنصر يستخدم لحماية الدوائر الكهربائية المفتاح المغناطيسي Reed Switch
المفتاح المغناطيسي ​

 

PC Serial Port Receiver


This circuit was designed to control a 32 channel Christmas light
show from the PC serial port. Originally designed with TTL logic,
it has been simplified using CMOS circuits to reduce component
count. It is a fairly simple, reliable circuit that requires only
4 common CMOS chips (for 8 outputs), an optical isolator, and a
few discrete components. The schematic diagram (SERIAL.GIF)
illustrates the circuit with 16 outputs which can be expanded with
additional 8 bit shift registers.

Disclaimer

This circuit requires physical connections be made to the
computer's serial port (COM1 or 2). To the best of my knowledge,
it is difficult to cause damage to yourself or your computer
by improper connections to this port, but there is no guarantee
that damage will not result. Use caution when making any external
electrical connections.

Basic RS232 serial transmission

Serial data is transmitted from the PC as a series of positive and
negative voltages on a single wire which occur at predetermined
times established by the baud rate. Both the transmitter and
receiver must be operating at the same baud rate so that the
receiver knows when to expect the next bit of information. For the
PC serial port, baud rate and bit rate are the same thing, but this
is not necessarily true with modems that can detect more than two
states of the line.

In the quiescent state, with no load on the line, the voltage on
the transmit line (pin 2 of the 25 pin connector) will be about
-12 relative to the signal ground (pin 7), which corresponds to a
logical "1". The output impedance of the serial port is about 1K
ohm which yields about 6 milliamps at 6 volts. A typical data
transmission frame consists of a start bit, 8 data bits, and one
to three stop bits. The start bit which is always positive,
signals the beginning of the transmission and is used by the
receiver to synchronize the clock so that the data bits can be
sampled at the proper times. After the 9th time interval passes
(start bit plus 8 data bits) a dead time occurs which allows the
receiver time to get ready for the next character. This dead time
is referred to as a stop bit, which is always negative or the same
as the quiescent state. The circuit described here requires two
stop bits of dead time for reliable operation. More sophisticated
circuitry would require only one.

Transmitted character examples

The letter "A" has a ASCII decimal value of 65. The "1" and "64"
bits are transmitted as a negative voltage (logical "1"), and the
others are transmitted as a positive voltage (logical "0").
64 + 1 = 65 = "A"

+ _____ _____________________________ _____
| | | | | |
| | | | | |
- ----- ----- ----- ---------
Start D0 D1 D2 D3 D4 D5 D6 D7 Stop Stop

Decimal value 1 2 4 8 16 32 64 128

Receiver's
Clock _______ __ __ __ __ __ __ __ ____________
| | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | |
-- -- -- -- -- -- -- --

The letter "B" has a ASCII decimal value of 66. The "2" and "64"
bits are transmitted as a negative voltage (logical "1"), and the
others are transmitted as a positive voltage (logical "0").
64 + 2 = 66 = "B"

+ ___________ _______________________ _____
| | | | | |
| | | | | |
- ----- ----- ----- ---------
Start D0 D1 D2 D3 D4 D5 D6 D7 Stop Stop


Circuit operation

The input terminals (pins 1 and 2) of the optical isolator are
connected through a 1K resistor to the transmit and signal ground
pins of the PC's serial port (pins 2 and 7 of the 25 pin connector).
A small signal diode is connected across the isolator input
terminals to protect the isolator from reverse voltage. In the
idle state, the isolator input voltage will be about -0.7 volts
and the isolator LED and transistor will be off. When a start bit
is received, about 5 milliamps will flow through the isolator LED
causing the isolator transistor to conduct at about 80 microamps
which in turn causes the external switching transistor (Q1) to
turn off. The rising voltage at the collector of Q1 is coupled
through a 510 pF capacitor to produce a narrow positive pulse
which sets the Q output of the first RS data latch (1/2 CD4013)
and enables the dual NAND gate clock oscillator.

The clock oscillator runs at a frequency equal to the baud rate
(9600 Hz) and must maintain a frequency accuracy of less than 5%
over the temperature range. High stability R and C components
are recommended.

The clock output is delayed by one cycle so that the start bit
will not be received as a valid data bit. This is accomplished
by the two remaining NAND gates (1/2 CD4093) and the second RS
data latch (1/2 CD4013). One of these gates is used to invert
the clock phase so that the first clock edge seen by the latch
(clock pin 11) will be going the wrong direction and so ignored.
The remaining gate, which is enabled by the second latch, opens on
the third clock edge, but also inverts the clock phase, and so
supplies a falling clock edge to the counter and shift registers
which is again the wrong direction, and is ignored. The fourth
clock edge will be rising and active and will occur near the
middle (about 52 microseconds) of the first data bit which will be
shifted into the registers. The remaining 7 bits are shifted into
the registers on each successive rising clock edge. Data is
inverted at the register outputs, a logical "1" will correspond to
zero volts, and a logical "0" will correspond to +6 volts.
Transmitting character (255) will set all outputs low, and
transmitting character (0) will set them all high.

The 4017 decade counter increments one count on each rising clock
edge and resets both data latches on the 8th edge. This in turn
stops the clock and resets the counter, and the circuit remains in
a waiting state until the next start bit arrives. Two stop bits of
dead time are required to allow the voltage at the input of the
NAND gate (pin 2) to reach a logic "1" before the next start bit
arrives. Erratic operation may occur when 2 or more characters are
transmitted as a string and only one stop bit is used.

The circuit may be modified to run at different baud rates by
adjusting the clock frequency. This can be accomplished by
temporally connecting pin 6 of the CD4013 to the positive supply
and then selecting R and C values for the desired frequency. You
may need to use a 1% resistor or a couple 5% resistors in series
or parallel to get the value close enough. Or use a variable
resistor in series of about 10% the total value.

At 9600 baud, data output at the shift registers will be unstable
for about a millisecond per word while the incoming data bits
are shifted into the registers and the existing bits are shifted
out (into bit heaven). Higher baud rates will reduce this time
proportionally and the original circuit operates at 57.6K baud
to eliminate a slight flickering of the lights which was noticed
at 9600.

The 74HCT164 shift register outputs will sink or source about
4 milliamps at 6 volts which can be increased with medium power
transistors or FETs to drive relay coils, incandescent lights
and other electronic devices. If relays are used, a small signal
diode will need to be added across the relay coil to suppress
the inductive voltage.

Power supply

It is recommended that 0.1 uF capacitors be installed near the
power pins of each CMOS device and a well regulated/filtered power
supply be used. For test purposes, a 6 volt battery will work
but the clock frequency will change slightly with power supply
voltage variations.

CD4011 Quad NAND gate

14 | Vdd
________|_______
| |
| CD4011 |
| |____ |
1 -----|----| \ |
| | 0 ---|----- 3
2 -----|----|____/ |
| | |
| |
| |____ |
5 -----|----| \ |
| | 0 ---|----- 4
6 -----|----|____/ |
| | |
| |
| |____ |
8 -----|----| \ |
| | 0 ---|----- 10
9 -----|----|____/ |
| | |
| |
| |____ |
12 -----|----| \ |
| | 0 ---|----- 11
13 -----|----|____/ |
| | |
|________________|
|
7 | Vss

CD4013 Dual 'D' Type Flip-Flop

14 | Vdd
________|_______
| |
6 -----| Set 1 Q1 |-----1
5 -----| D1 |
3 -----| Clock 1 _ |
4 -----| Reset 1 Q1 |-----2
| |
| CD4013 |
| |
8 -----| Set 2 Q2 |-----13
9 -----| D2 |
11 -----| Clock 2 _ |
10 -----| Reset 2 Q2 |-----12
|________________|
|
7 | Vss

CD4017 Decade Counter/Divider

16 | Vdd
________|_______
| |
| CD4017 |
| |
| "0" |----- 3
| "1" |----- 2
| "2" |----- 4
14 -----| Clock "3" |----- 7
| "4" |----- 10
13 -----| Clock "5" |----- 1
| Enable "6" |----- 5
| "7" |----- 6
15 -----| Reset "8" |----- 9
| "9" |----- 11
| Carry out |----- 12
|________________|
|
8 | Vss

74HCT164 8 Bit Serial-In / Parallel-Out Shift Register

14 | Vdd
________|_______
| |
| 74HCT164 |
| |
1 -----| AND Gated Q0 |----- 3
| Serial Q1 |----- 4
2 -----| Inputs Q2 |----- 5
| Q3 |----- 6
| Q4 |----- 10
9 ----0| Reset Q5 |----- 11
| Active Q6 |----- 12
| Low Q7 |----- 13
| |
8 -----| Clock |
|________________|
|
7 | Vss

Serial port male D-SUB connectors as seen from outside the PC.

1 13 1 5
_____________________________ _____________
( . . . . . . . . . . . . . ) ( . . . . . )
\ . . . . . . . . . . . . / \ . . . . /
------------------------- ---------
14 25 6 9

Name Output/Input 25 pin 9 pin
---------------------------------------------------------
Transmit Data O 2 3
Receive Data I 3 2
Request To Send O 4 7
Clear To Send I 5 8
Data Terminal Ready O 20 4
Data Set Ready I 6 6
Ring Indicator I 22 9
Data Carrier Detect I 8 1
Signal ground - 7 5
Power line ground - 1 -

QBasic test program for 8 bit receiver

CLS
DEFINT A-Z
PRINT "Test sequence in progress, press any key to quit."
OPEN "COM1:9600,n,8,2,CD0,CS0,DS0,OP0,RS,TB2048" FOR OUTPUT AS #1
Sequence:
FOR Bit = 0 TO 7
PRINT #1, CHR$(255 - (2 ^ Bit)); ' Set one of 8 outputs high.
SLEEP 1 ' Wait 1 sec between characters.
IF INKEY$ <> "" THEN CLOSE : SYSTEM
NEXT Bit
GOTO Sequence
END

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PC Serial Receiver (57.6K Baud / TTL & CMOS)


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Parallel Port Relay Interface

Below are three examples of controlling a relay from the PC's parallel printer port (LPT1 or LPT2). Figure A shows a solid state relay controlled by one of the parallel port data lines (D0-D7) using a 300 ohm resistor and 5 volt power source. The solid state relay will energize when a "0" is written to the data line. Figure B and C show mechanical relays controlled by two transistors. The relay in figure B is energized when a "1" is written to the data line and the relay in figure C is energized by writing a "0" to the line. In each of the three circuits, a common connection is made from the negative side of the power supply to one of the port ground pins (18-25).
There are three possible base addresses for the parallel port You may need to try all three base addresses to determine the correct address for the port you are using but LPT1 is usually at Hex 0378. The QBasic "OUT" command can be used to send data to the port. OUT, &H0378,0 sets D0-D7 low and OUT, &H378,255 sets D0-D7 high. The parallel port also provides four control lines (C0,C1,C2,C3) that can be set high or low by writing data to the base address+2 so if the base address is Hex 0378 then the address of the control latch would be Hex 037A. Note that three of the control bits are inverted so writing a "0" to the control latch will set C0,C1,C3 high and C2 low.

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FM Beacon Broadcast Transmitter (88-108 MHz)

This circuit will transmit a continuous audio tone on the FM broadcast band (88-108 MHz) which could used for remote control or security purposes. Circuit draws about 30 mA from a 6-9 volt battery and can be received to about 100 yards. A 555 timer is used to produce the tone (about 600 Hz) which frequency modulates a Hartley oscillator. A second JFET transistor buffer stage is used to isolate the oscillator from the antenna so that the antenna position and length has less effect on the frequency. Fine frequency adjustment can be made by adjusting the 200 ohm resistor in series with the battery. Oscillator frequency is set by a 5 turn tapped inductor and 13 pF capacitor. The inductor was wound around a #8 X 32 bolt (about 3/16 diameter) and then removed by unscrewing the bolt. The inductor was then streached to about a 3/8 inch length and tapped near the center. The oscillator frequency should come out somewhere near the center of the band (98 MHz) and can be shifted higher or lower by slightly expanding or compressing the inductor. A small signal diode (1N914 or 1N4148) is used as a varactor diode so that the total capacity in parallel with the inductor varies slightly at the audio rate thus causing the oscillator frequency to change at the audio rate (600 Hz). The ramping waveform at pins 2 and 6 of the timer is applied to the reversed biased diode through a large (1 Meg) resistor so that the capacitance of the diode changes as the ramping voltage changes thus altering the frequency of the tank circuit. Alternately, an audio signal could be applied to the 1 Meg resistor to modulate the oscillator but it may require an additional pullup resistor to reverse bias the diode. The N channel JFET transistors used should be high frequency VHF or UHF types (Radio Shack #276-2062 MPF102) or similar.

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12 Volt Lamp Dimmer

Here is a 12 volt / 2 amp lamp dimmer that can be used to dim a standard 25 watt automobile brake or backup bulb by controlling the duty cycle of a astable 555 timer oscillator. When the wiper of the potentiometer is at the uppermost position, the capacitor will charge quickly through both 1K resistors and the diode, producing a short positive interval and long negative interval which dims the lamp to near darkness. When the potentiometer wiper is at the lowermost position, the capacitor will charge through both 1K resistors and the 50K potentiometer and discharge through the lower 1K resistor, producing a long positive interval and short negative interval which brightens the lamp to near full intensity. The duty cycle of the 200 Hz square wave can be varied from approximately 5% to 95%. The two circuits below illustrate connecting the lamp to either the positive or negative side of the supply.

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Automatic 12 Volt Lamp Fader

This circuit is similar to the "Fading Red Eyes" circuit (in the LED section) used to fade a pair of red LEDs. In this version, the lamps are faded by varying the duty cycle so that higher power incandescent lamps can be used without much power loss. The switching waveform is generated by comparing two linear ramps of different frequencies. The higher frequency ramp waveform (about 75 Hz.) is produced from one section of the LM324 quad op-amp wired as a Schmitt trigger oscillator. The lower frequency ramp controls the fading rate and is generated from the upper two op-amps similar to the "fading eyes" circuit. The two ramp waveforms at pins 9 and 1 are compared by the 4th op-amp which generates a varying duty cycle rectangular waveform to drive the output transistor. A second transistor is used to invert the waveform so that one group of lamps will fade as the other group brightens. The 2N3053 will handle up to 500 milliamps so you could connect 12 strings of 4 LEDs each (48 LEDs) with a 220 ohm resistor in series with each group of 4 LEDs. This would total about 250 milliamps. Or you can use three 4 volt, 200 mA Xmas tree bulbs in series. For higher power 12 volt automobile lamps, the transistor will need to be replaced with a MOSFET that can handle several amps of current. See the drawing below the schematic for possible hookups.

Other possible hookups

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1.5 Hour Lamp Fader (Sunset Lamp)

Similar to the one above, the sunset lamp comes on at full brightness and then slowly fades out over 1.5 hours time and stays off until power is recycled.

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Sunrise Lamp

In this circuit, a 120VAC lamp is slowly illuminated over a approximate 20 minute period. The bridge rectifier supplies 120 DC to the MOSFET and 60 watt lamp. A 6.2K, 5 watt resistor and zener diode is used to drop the voltage to 12 volts DC for the circuit power. The bridge rectifier should be rated at 200 volts and 5 amps or more. In operation, a 700 Hz triangle waveform is generated at pin 1 of the LM324 and a slow rising voltage is obtained at pin 8. These two signals are compared at pins 12 and 13 to produce a varying duty cycle rectangular waveform at pin 14, which controls the MOSFET and brightness of the 60 watt lamp. When power is applied, the lamp will start to illuminate within a minute or so, and will slowly brighten to full intensity in about 20 minutes. You can make that longer or shorter with adjustments to the 270K resistor at pin 9. The 2.2 ohm resistor and .015uF cap connected to the lamp serve to supress RFI. The diode at pin 9 and 10K resistor on pin 8 are used to discharge the 3300uF cap when power is removed. Power should be off for a few minutes before re-starting.
Caution: This circuit is connected directly to the AC line and presents a hazard if any part is touched while connected to the line. Use caution and do not touch any parts while the circuit is connected to the AC line. You may want to use a 9 volt battery connected across the 12 volt zener to check the basic operation. The DC voltage at pins 1,2,3,5,6,7 will all be around 4.3 volts if the circuit is working correctly. If the DC voltages are all correct, you can use a variac to slowly apply the full line voltage and check for proper operation.

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Simple Op-Amp Radio

This is basically a crystal radio with an audio amplifier which is fairly sensitive and receives several strong stations in the Los Angeles area with a minimal 15 foot antenna. Longer antennas will provide a stronger signal but the selectivity will be worse and strong stations may be heard in the background of weaker ones. Using a long wire antenna, the selectivity can be improved by connecting it to one of the taps on the coil instead of the junction of the capacitor and coil. Some connection to ground is required but I found that standing outside on a concrete slab and just allowing the long headphone leads to lay on the concrete was sufficient to listen to the local news station (KNX 1070). The inductor was wound with 200 turns of #28 enameled copper wire on a 7/8 diameter, 4 inch length of PVC pipe, which yields about 220 uH. The inductor was wound with taps every 20 turns so the diode and antenna connections could be selected for best results which turned out to be 60 turns from the antenna end for the diode. The diode should be a germanium (1N34A type) for best results, but silicon diodes will also work if the signal is strong enough. The carrier frequency is removed from the rectified signal at the cathode of the diode by the 300 pF cap and the audio frequency is passed by the 0.1uF capacitor to the non-inverting input of the first op-amp which functions as a high impedance buffer stage. The second op-amp stage increases the voltage level about 50 times and is DC coupled to the first through the 10K resistor. If the pairs of 100K and 1 Meg resistors are not close in value (1%) you may need to either use closer matched values or add a capacitor in series with the 10K resistor to keep the DC voltage at the transistor emitter between 3 and 6 volts. Another approach would be to reduce the overall gain with a smaller feedback resistor (470K). High impedance headphones will probably work best, but walkman stereo type headphones will also work. Circuit draws about 10 mA from a 9 volt source. Germanium diodes (1N34A) types are available from Radio Shack, #276-1123.

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FM Beacon Broadcast Transmitter (88-108 MHz)

This circuit will transmit a continuous audio tone on the FM broadcast band (88-108 MHz) which could used for remote control or security purposes. Circuit draws about 30 mA from a 6-9 volt battery and can be received to about 100 yards. A 555 timer is used to produce the tone (about 600 Hz) which frequency modulates a Hartley oscillator. A second JFET transistor buffer stage is used to isolate the oscillator from the antenna so that the antenna position and length has less effect on the frequency. Fine frequency adjustment can be made by adjusting the 200 ohm resistor in series with the battery. Oscillator frequency is set by a 5 turn tapped inductor and 13 pF capacitor. The inductor was wound around a #8 X 32 bolt (about 3/16 diameter) and then removed by unscrewing the bolt. The inductor was then streached to about a 3/8 inch length and tapped near the center. The oscillator frequency should come out somewhere near the center of the band (98 MHz) and can be shifted higher or lower by slightly expanding or compressing the inductor. A small signal diode (1N914 or 1N4148) is used as a varactor diode so that the total capacity in parallel with the inductor varies slightly at the audio rate thus causing the oscillator frequency to change at the audio rate (600 Hz). The ramping waveform at pins 2 and 6 of the timer is applied to the reversed biased diode through a large (1 Meg) resistor so that the capacitance of the diode changes as the ramping voltage changes thus altering the frequency of the tank circuit. Alternately, an audio signal could be applied to the 1 Meg resistor to modulate the oscillator but it may require an additional pullup resistor to reverse bias the diode. The N channel JFET transistors used should be high frequency VHF or UHF types (Radio Shack #276-2062 MPF102) or similar.

​

 

12 Volt Lamp Dimmer

Here is a 12 volt / 2 amp lamp dimmer that can be used to dim a standard 25 watt automobile brake or backup bulb by controlling the duty cycle of a astable 555 timer oscillator. When the wiper of the potentiometer is at the uppermost position, the capacitor will charge quickly through both 1K resistors and the diode, producing a short positive interval and long negative interval which dims the lamp to near darkness. When the potentiometer wiper is at the lowermost position, the capacitor will charge through both 1K resistors and the 50K potentiometer and discharge through the lower 1K resistor, producing a long positive interval and short negative interval which brightens the lamp to near full intensity. The duty cycle of the 200 Hz square wave can be varied from approximately 5% to 95%. The two circuits below illustrate connecting the lamp to either the positive or negative side of the supply.

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Automatic 12 Volt Lamp Fader

This circuit is similar to the "Fading Red Eyes" circuit (in the LED section) used to fade a pair of red LEDs. In this version, the lamps are faded by varying the duty cycle so that higher power incandescent lamps can be used without much power loss. The switching waveform is generated by comparing two linear ramps of different frequencies. The higher frequency ramp waveform (about 75 Hz.) is produced from one section of the LM324 quad op-amp wired as a Schmitt trigger oscillator. The lower frequency ramp controls the fading rate and is generated from the upper two op-amps similar to the "fading eyes" circuit. The two ramp waveforms at pins 9 and 1 are compared by the 4th op-amp which generates a varying duty cycle rectangular waveform to drive the output transistor. A second transistor is used to invert the waveform so that one group of lamps will fade as the other group brightens. The 2N3053 will handle up to 500 milliamps so you could connect 12 strings of 4 LEDs each (48 LEDs) with a 220 ohm resistor in series with each group of 4 LEDs. This would total about 250 milliamps. Or you can use three 4 volt, 200 mA Xmas tree bulbs in series. For higher power 12 volt automobile lamps, the transistor will need to be replaced with a MOSFET that can handle several amps of current. See the drawing below the schematic for possible hookups.


Other possible hookups


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1.5 Hour Lamp Fader (Sunset Lamp)

Similar to the one above, the sunset lamp comes on at full brightness and then slowly fades out over 1.5 hours time and stays off until power is recycled.

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Sunrise Lamp

In this circuit, a 120VAC lamp is slowly illuminated over a approximate 20 minute period. The bridge rectifier supplies 120 DC to the MOSFET and 60 watt lamp. A 6.2K, 5 watt resistor and zener diode is used to drop the voltage to 12 volts DC for the circuit power. The bridge rectifier should be rated at 200 volts and 5 amps or more. In operation, a 700 Hz triangle waveform is generated at pin 1 of the LM324 and a slow rising voltage is obtained at pin 8. These two signals are compared at pins 12 and 13 to produce a varying duty cycle rectangular waveform at pin 14, which controls the MOSFET and brightness of the 60 watt lamp. When power is applied, the lamp will start to illuminate within a minute or so, and will slowly brighten to full intensity in about 20 minutes. You can make that longer or shorter with adjustments to the 270K resistor at pin 9. The 2.2 ohm resistor and .015uF cap connected to the lamp serve to supress RFI. The diode at pin 9 and 10K resistor on pin 8 are used to discharge the 3300uF cap when power is removed. Power should be off for a few minutes before re-starting.
Caution: This circuit is connected directly to the AC line and presents a hazard if any part is touched while connected to the line. Use caution and do not touch any parts while the circuit is connected to the AC line. You may want to use a 9 volt battery connected across the 12 volt zener to check the basic operation. The DC voltage at pins 1,2,3,5,6,7 will all be around 4.3 volts if the circuit is working correctly. If the DC voltages are all correct, you can use a variac to slowly apply the full line voltage and check for proper operation.

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Simple Op-Amp Radio

This is basically a crystal radio with an audio amplifier which is fairly sensitive and receives several strong stations in the Los Angeles area with a minimal 15 foot antenna. Longer antennas will provide a stronger signal but the selectivity will be worse and strong stations may be heard in the background of weaker ones. Using a long wire antenna, the selectivity can be improved by connecting it to one of the taps on the coil instead of the junction of the capacitor and coil. Some connection to ground is required but I found that standing outside on a concrete slab and just allowing the long headphone leads to lay on the concrete was sufficient to listen to the local news station (KNX 1070). The inductor was wound with 200 turns of #28 enameled copper wire on a 7/8 diameter, 4 inch length of PVC pipe, which yields about 220 uH. The inductor was wound with taps every 20 turns so the diode and antenna connections could be selected for best results which turned out to be 60 turns from the antenna end for the diode. The diode should be a germanium (1N34A type) for best results, but silicon diodes will also work if the signal is strong enough. The carrier frequency is removed from the rectified signal at the cathode of the diode by the 300 pF cap and the audio frequency is passed by the 0.1uF capacitor to the non-inverting input of the first op-amp which functions as a high impedance buffer stage. The second op-amp stage increases the voltage level about 50 times and is DC coupled to the first through the 10K resistor. If the pairs of 100K and 1 Meg resistors are not close in value (1%) you may need to either use closer matched values or add a capacitor in series with the 10K resistor to keep the DC voltage at the transistor emitter between 3 and 6 volts. Another approach would be to reduce the overall gain with a smaller feedback resistor (470K). High impedance headphones will probably work best, but walkman stereo type headphones will also work. Circuit draws about 10 mA from a 9 volt source. Germanium diodes (1N34A) types are available from Radio Shack, #276-1123.

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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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