Hobby in Electronics

Capacitor Code Calculator

2013-04-10T01:24:00.002+06:00

Capacitor is a two terminal passive electrical component. It is used to store energy in an electrical field. Capacitor works as a voltage source. The capacitor is used widely and its forms contains at least two electrical conductor separated by a dielectric material, one common construction consists of metal foils separated by a thin layer of insulating film. In electrical circuit capacitors are widely used as a parts.

The static electric field develops across the Di-electric when the voltage or potential difference is applied across the terminals. This occurs when negative charge is on one plate and positive charge on the other plate. Mainly electrical energy is stored in the electrostatic field. An ideal capacitor is characterized by a single constant value capacitance and measured in farads. So we need to know the measurements of capacitor value using the figure. For more information go wikipedia.

Remote Control Regulated Ceiling Fan Circuit Diagram

2013-02-04T19:25:00.001+06:00

The main objectives are - to control the switch using remote as an on/off switch. To determine that the infrared sensor can easily receive the signal from the remote transmitter and to control the Fan speed using regulator.

The 38 kHz infrared rays generated by the remote control are received by IR receiver. Pin 2 of IR is connected to ground, pin 3 is connected to the power supply through R1 and the output is taken from pin 1. The output pulse is set to pin 2 of 555 timers.

Then in pin 2 if the voltage is less than one third of Vcc, a trigger pulse is active.The pulse signal is fed to clock pin 4 of counter IC 74109. Pin 8 of 74109 IC is grounded, pin 16 is connected to Vcc and pin 3 is grounded. The output of 74109 IC is taken from its pin 7. Q1 connected to pin 7 through R3 of IC 74109 drives the relay RL.

The relay is connected through a fan and a regulator. It gets connected to live terminal of AC mains via normally opened (N/O) contact when the relay energizes. If we want to operate a DC 12 volt relay then we have to use a regulated DC 12 volt power supply for DC 12 volt Relay and we have to remember that the circuit voltage not be exceeded more than DC 5 volts.

Fig: Layout of Remote control regulated Ceiling Fan

JK flipflop/IC 74109:

The 74109 are dual positive-edge triggered, JK flip-flops with individual J, K inputs, clock (CP) inputs, set (SD) and reset (RD) inputs; also complementary Q and Q outputs.The set and reset are asynchronous active LOW inputs and operate independently of the clock input. The J and K inputs control the state changes of the flip-flops as described in the mode select function table. The JK design allows operation as a T-type flip-flop by tying the J and K inputs together. In the T Flip-flop sequentially if the i/p is 1, the o/p is 1, then o/p is 0 and again 1.

IR Remote Control Home Appliance Circuit Diagram

2012-11-06T18:06:00.003+06:00

This is the most popular IR Remote control circuit for home appliances like lamp, fan, radio, tv etc to make the appliance turn on/off from a TV, VCD or DVD remote control. It is very simple to build because of few components and simple design.

The circuit can activated from up to 10 metres. The 38kHz infrared (IR) rays generated by the remote control are received by IR receiver module TSOP1738 of the circuit. Pin 1 of TSOP1738 is connected to ground, pin 2 is connected to the power supply through resistor R5 and the output is taken from pin 3. The output signal is amplified by transistor T1 (BC558).

The amplified signal is fed to clock pin 14 of decade counter IC CD4017 (IC1). Pin 8 of IC1 is grounded, pin 16 is connected to Vcc and pin 3 is connected to LED1 (red), which glows to indicate that the appliance is ‘off.’ The output of IC1 is taken from its pin 2. LED2 (green) connected to pin 2 is used to indicate the ‘on’ state of the appliance. Transistor T2 (BC548) connected to pin 2 of IC1 drives relay RL1. Diode IN 4148 acts as a freewheeling diode. The appliance to be controlled is connected between the pole of the relay and neutral terminal of mains. It gets connected to live terminal of AC mains via normally opened (N/O) contact when the relay energises. you can use any NPN transistor inplace of BC548. You can also use SL100 or any NPN transistor lying around you.

The delay depends on the C1 capacitor. Using higher value capacitor will create more delay and using less value capacitor will switch the circuit more than 2 times when you press a remote. Analyse the circuit by placing the 10uf capacitor in place of C1 (100uf).

Automatic Dark Activated LED Light Circuit Diagram using 555 Timer

2012-10-09T20:12:00.001+06:00

555 Timer Touch Activated Alarm Circuit Diagram

2012-07-15T03:54:00.004+06:00

This is the circuit diagram of touch activated alarm system which still activated on load shedding. Alarm system will be activated when someone touch the “touch plate” which is called trigger. In this circuit the most updated part is automatic battery activator which is made by a relay. So don’t upset on load shedding you alarm system is activated. This circuit could be used at your home door, locker, vehicle or metal gate etc.

Automatic Emergency Light Circuit Diagram

2012-05-15T12:08:00.001+06:00

This is the simple circuit of automatic emergency light. It is called dark dependent circuit. A 555 timer IC and LDR is used for this configuration. When light fall on the LDR, its resistance is decrease and in dark position its resistance is going high. Using these characteristics of LDR, automatic emergency light is made.

LDR is called Light Dependent Resistor. Its resistance is inversely proportional to the falling light on its surface. In dark, its resistance is approximately 7k to 10k. When light fall on its surface, its resistance is decrease to less than 1k. In the circuit, a voltage divider arrangement circuit is used here with LDR and 10K variable resistor.

When light fall on the surface of LDR, the resistance decrease to 1k. So the voltage of the timer pin-6 is greater than 2/3 of +V_cc. For this reason the output pin-3 goes low. The base voltage of transistor BC547 is less than 0.75 volt. The transistor is OFF state. So the light is OFF.

In dark position the LDR resistance increase is high so the voltage of the trigger pin-2 decrease to less than 1/3 of +V_cc. The output pin-3 goes high so the base voltage of the transistor BC547 is greater than 0.75 volt. The transistor is ON state. So the light is ON and it emits light.

Digital Object Counter using LDR and digital IC 7490

2012-05-04T09:58:00.000+06:00

This is the simple circuit on Hobby Electronics. In this circuit three modules are used in object counter. 555 timer are used as a monostable mode and astable mode. The other is counter module.

In this circuit 555 timer configured as a monostable mode, is a simple automatic dark sensor circuit that gives output when light falling is blocked on LDR. Pin 3 of monostable circuit has been connected to pin 4 of astable timer. When monostable circuit generates output, astable mode timer starts giving pulses to the counter module. Frequency for counter module is set up using R4, R3 and C2.

7490 acts as a decade counter and 7447 uses the output of 7490 to display numbers on seven segment display. This circuit counts from 0 to 9. You can count 0 to 100 modifying counter module circuit. Just adding few components as well as two counter ic, two display driver and two display. For count 0 to 100, comments on the comments box. You will get complete circuit.

The output will be: If you block light falling on LDR, the number on seven segment display will increase.

4017 LED Knight Rider Running Light Circuit Diagram

2012-04-29T10:36:00.002+06:00

In this 4017 Knight Rider circuit, the 555 timer is wired as an oscillator. It can be adjusted to give the desired speed for the display. The output of the 555 is directly connected to the input of a Johnson Counter (CD 4017).

The input of the counter is called the CLOCK line. The 10 outputs become active, one at a time, on the rising edge of the waveform from the 555. Each output can deliver about 20mA but a LED should not be connected to the output without a current-limiting resistor (220Ω in the circuit above).

The first 6 outputs of the chip are connected directly to the 6 LEDs and these “move” across the display. The next 4 outputs move the effect in the opposite direction and the cycle repeats. The animation above shows how the effect appears on the display. Using six LEDs, the display can be placed in the front of a model car to give a very realistic effect. The outputs can be taken to driver transistors to produce a larger version of the display.

Mobile Incoming Call Indicator Circuit Diagram

2012-04-20T14:48:00.000+06:00

This circuit can be used to escape from the nuisance of mobile phone rings when you are at home. This circuit will give a visual indication if placed near a mobile phone even if the ringer is deactivated.

When a call is coming to the mobile phone, the transmitter inside it becomes activated. The frequency of the transmitter is around 900MHz.The coil L1 picks up these oscillations by induction and feds it to the base of Q1. This makes the transistor Q1 activated.Since the Collector of Q1 is connected to the pin 2 of IC1 (NE555) , the IC1 is triggered to make the LED connected at its output pin (pin 3) to blink. The blinking of the LED is the indication of incoming call.

Notes:

The coil L1 can be made by making 150 turns of 36 SWG enameled copper wire on a 5mm dia plastic former.Or you can purchase a 10 uH coil from shop if available.
The circuit can be powered from a 6V battery.
Assemble the circuit on a good quality PCB.
C1 & C3 are to be polyester capacitors.
The electrolytic capacitor C2 must be rated 10V.

Automatic Street Light Controller Circuit Diagram

2012-03-25T21:44:00.004+06:00

This circuit is an automatic street light controller. Sensors used to detect changes in light is LDR (Light dependent resistor), the working principle of Light dependent resistor is exposed to light when the resistance value of LDR great, but if not exposed to light or dark then the resistance value of LDR.

LDR is a special type of resistance whose value depends on the brightness of the light which is falling on it. It has resistance of about 1 mega ohm when in total darkness, but a resistance of only about 5k ohms when brightness illuminated. It responds to a large part of light spectrum.

When light falls on the LDR then its resistance decreases which results in increase of the voltage at pin 2 of the IC 555. IC 555 has got comparator inbuilt, which compares between the input voltage from pin2 and 1/3rd of the power supply voltage. When input falls below 1/3rd then output is set high otherwise it is set low. Since in brightness, input voltage rises so we obtain no positive voltage at output of pin 3 to drive relay.

Complete Room Securty System Circuit diagram

2012-03-14T17:47:00.015+06:00

This simple circuit is called room security system circuit. The main purpose of this circuit is to secure your room in night. You need not any security guard. When any unwanted person wants to enter your room in night then this circuit raised alarm. On the other benefit, it is always activated on load shedding.

There are five separates parts in this circuit – regulated power supply, relay driver, door switching, alarm system and audio amplifier. First section is regulated power supply. The output of IC 7809 is regulated +9Volt which is converted from 9Volt unregulated power supply. Capacitors are used for removing ripple. A full wave 9 volt transformer is connected in the input of this power section.

The second part is relay driver. Q1 transistor is used for driving relay. When the Q1 transistor is forward bias then the relay is ON and the total circuit gets positive voltage from ac source. In the time of load shedding relay is deactivated and the total circuit gets power from 6Volt Battery.

The third part is door switching. When C1 capacitor’s two terminals are short, transistor Q2 is reversed biased. So Q2 transistor is OFF. When C1 capacitor’s two terminals are open, transistor Q2 is forward biased. So Q2 transistor is ON. For this reason IC UM66 is ON and it generates music which is feed another two transistors Q3 and Q4. A speaker is connected with collector of the transistor Q4 as circuit diagram.

Freeze Protector Circuit

2012-01-24T22:53:00.006+06:00

This is the simple freeze protector circuit diagram. It is also called timing circuit. It is just hobby project for beginners. When you need to operate automatically any device in the fixed time later after coming AC power supply, you can use this circuit.

The voltage amplitude is high when AC power come. Suddenly high voltage destroys the electronics device. For this reason, in the time of load shedding we need to switched off electronics device (Audio/Video player, CD/DVD Player, TV, Freeze or any electronics device). This circuit solve this problem.

Hobby Electronics helps the beginners to know the timing circuit specially using 555 IC timer. NE555 IC is the very simple well known parts. Its configuration is very simple. You can use this timer any simple circuit.

In this circuit use 12volt power supplies. 300k variable resistor is used for timing control. Timing resistor and capacitor are 300k and 1000uF. Only change the value of the variable resistor for your required timing.

The circuit output pin 3 is connected with resistor (10k) and output 12 volt relay. Relay is connected as figured with the device. Making cost is too low. Anyone can make this circuit easily.

Dual Voltage Power Supply 12 Volt

2012-01-19T01:06:00.009+06:00

This is the simple circuit diagram of Dual Voltage Power Supply. It is used for Misc… application. This circuit is called regulated power supply. For this reason the main component of this circuit is Regulator IC. It also needs few components to built. The regulator 7812 is the positive voltage regulator and 7912 is the negative voltage regulator.

You can also use 7809 for 9 volt positive power supply and 7909 for negative voltage power supply.

It regulates voltage from 24Volt to 12 Volt (DC). The transformer input is 110Volt to 220Volt (AC) and the output must be between 12Volt to 24Volt (AC) and current must be 500mA. In this circuit some capacitors are used as a filter for removing repole.

Simple AM Transmitter Circuit

2011-10-31T07:21:00.011+06:00

AM transmitter circuit that can transmit your audios to your backyard.This circuit is designed with limited the power output to match the FCC regulations and still produces enough amplitude modulation of voice in the medium wave band to satisfy your personal needs. You will love this.

The circuit has two parts , an audio amplifier and a radio frequency oscillator. The oscillator is built around Q1 (BC109) and related components. The tank circuit with inductance L1 and capacitance VC1 is tunable in the range of 500kHz to 1600KHz.

These components can be easily obtained from your old medium wave radio. Q1 is provided with regenerative feedback by connecting the base and collector of Q1 to opposite ends of the tank circuit. C2 ,the 1nF capacitance , couples signals from the base to the top of L1, and C4 the 100pF capacitance ensures that the oscillation is transfered from collector, to the emitter, and through the internal base emitter resistance of the transistor Q2 (BC 109) , back to the base again.

The resistor R7 has a vital part in this circuit. It ensures that the oscillation will not be shunted to ground trough the very low value internal emitter resistance, re of Q1(BC 109), and also increases the input impedance such that the modulation signal will not be shunted to ground.

Q2 is wired as a common emitter RF amplifier, C5 decouples the emitter resistance and unleashes full gain of this stage. The microphone can be electret condenser microphone and the amount of AM modulation can be adjusted by the 4.7 K variable resistanceR5.

AM Receiver Circuit Diagram Using ZN414 IC

2011-10-08T16:17:00.009+06:00

A.M. Antenna coil and MW gang connected in parallel. One common point of this parallel circuit connected to the IC ZN414 pin number 2.

Another common point of that parallel circuit connected with two resistors (100kΩ, 1kΩ) in series. A capacitor is connected with the common point of resistors (100kΩ, 1kΩ). A capacitor is connected in series with base of the transistor and the pin number 1 of the ZN414.

One end of the 10kΩ resistor is connected with the collector point of the transistor BC549 and another end is connected with the power supply +Vcc.

And one end of the 100kΩ resistor is connected with the collector and another end connected with base. 105pF capacitor is connected between collector and ground. Pin 3 of IC ZN414 and emitter of the transistor is connected to the ground.

Required Instrument

IC ZN 414.
Capacitor(105pF×1,104pF×2,103pF×1)
MW Gang
Resistor(100kΩ×2,10kΩ×1,1kΩ×1,470Ω×1)
AM antenna
Transistor(BC549)

AM Transmitter Circuit Diagram Using 741 Op-amp

2011-09-24T12:13:00.007+06:00

AM transmitter is a circuit which can transmit message signal to modulated signal. This circuit is designed with limited power and the required power supply of the transmitter circuit is 9 Volt.

The circuit has three parts that is an audio amplifier, radio frequency oscillator and modulator circuit. The frequency oscillator is built with 741 Op-amp and related components. The carrier signal frequency and its amplitude can be varied using variable resistor accordance with V_R1 and V_R2respectively. C₁ and C₂ are the main components to generate the carrier frequency.

Another part of the circuit is an audio amplifier circuit. The audio amplifier is built with 741 Op-amp and related components. A microphone is used to convert the voice signal to the audio signal which is feed to the op-amp’s inverting terminal. This audio signal is amplified by the op-amp. The amplified audio signal is filtered using the capacitor C₇. This output is feed to the modulator circuit.

The main part of the AM transmitter is modulator circuit which is built with the transistor BC109. The carrier signal is feed to the base of transistor and the message / audio signal is also feed to the emitter of the transistor.

Here the required modulated signal is taken from the collector of the transistor which is feed to the output antenna.

Luggage Protector Circuit Using 555 Timer IC

2011-08-30T23:13:00.007+06:00

The circuit is called protector alarm circuit to protect from the theft of your luggage or bags. This circuit is built electronically using 555 timer IC. The alarm will rise highly when the thin wire is cut off by the thief. The circuit configuration using 555 timer IC acts as a astable multivibrator which produce signal tone of frequency of about 1 KHz and produce sound like a shrill noise away the output speaker.

If you need to know 555 Timer configuration click here and download

IC’s 5number pin is directly connected to the power supply. 10k, 68k resistor and 0.01uf capacitor are connected to generate specific range of frequency like as 1KHz. You can change output frequency by changing the value of resistor and capacitor. Pin 1 is directly connected to the ground. Output is taken from pin 3. A 8Ohms speaker is connected to the output for alarm sound. Thin wire is connected as shown in figure.

The wire would be very thin copper like 36 SWG or higher. You can use one gage of normal wire. The driving voltage of the circuit is 5 Volt to 12 Volt.

Transistor AM Modulator Circuit Diagram

2011-08-29T22:16:00.004+06:00

Modulation is the process of changing some characteristics (e.g. amplitude, frequency or phase) of a carrier wave in accordance with the intensity of the signal is known as modulation.

The figure shows the electronics circuit of a simple am modulator. It is essentially a CE amplifier having a voltage gain of A. The carrier signal is the input to the amplifier. The modulating signal is applied in the emitter resistance circuit.

The carrier e_c is applied at the input of the amplifier and the modulating signal e_s is applied in the emitter resistance circuit. The amplifier circuit amplifies the carrier by a factor A, so that the output is A_es. Since the modulating signal is a part of the biasing circuit, it products low frequency variations in the emitter circuit. This in turn causes variations in “A”.

The result is that amplitude of the carrier varies in accordance with the strength of the signal. Consequently, amplitude modulated output is obtained across R_L. It may be noted that carrier should not influence the voltage gain A; only the modulating signal should do this. To achieve this objective, carries should have a small magnitude and signal should have a large magnitude.

A.M Modulator Circuit Diagram

2011-08-17T14:21:00.003+06:00

Amplitude modulation is a process in which the amplitude of a carrier wave c(t) is varied about a mean value, linearly with the base-band signal m(t).

In amplitude modulation the amplitude of a high-frequency carrier is varied in direct proportion to the low-frequency (base-band) message signal. The carrier is usually a sinusoidal waveform that is,

C(t) = Ac . cos(wt)

Where, is the carrier amplitude and f_c is the carrier frequency.

The base-band signal or message signal is,

m(t) = A_m_.cos(wt)
Where, A_mis the amplitude of message signal and f_m is the frequency of message signal.

An amplitude modulation wave may thus be described in its most general form as the function of the time as follows,

S(t) = m(t)×c(t)

Mini Auto Charger Fan Circuit

2011-08-12T23:11:00.003+06:00

This circuit is called the auto circuit which can use any electronic device to operate it automatically. To make this circuit the cost is very low. Any interested student can make it very easily. The main component of this circuit is transistor. Its operation is very easy.

The main purpose of this is to operate a charger fan where need 6volt battery. This circuit is mainly needed when the main power is OFF. That is called load shedding. Because at the time of load shedding , 6volt battery operate the fan automatically. You don’t have need to ON the switch of the fan or OFF the fan switch. Only relay work this as a switch. The charging system is also automatically. On the other big matter is that no over charge is occurred of the battery. So the life time of the battery is increased.

Component:

1. Transistor ( npn ) – 2N2222, BC547

2. Zener Diode - 6.8V

3. Diode

4. Relay - 6V

5. Resistor – 1K, 100Ω

6. Rechargeable Battery - 6V

7. Fan - 6V

8. Power supply - 6V

Operation:

This circuit is three section, input section and output section. 2N2222 transistor is used to control relay. BC547 transistor is used to control output section using relay. Zener diode and a diode connect with BC547 transistor base as a series connection. Zener diode always controls battery charge. It zener voltage is 6.8V which can’t overcome battery voltage.

When power supply voltage is applied to the 2N2222 transistor base the transistor is on. So the relay is ON relatively the output circuit is OFF. Inverse will occurs when power supply voltage is OFF. When 2N2222 transistor is ON then relay active only battery charging, relay deactivate the fan. Zener diode always keeps battery voltage full (6volt).

Advantages:

1. Need not switch ON/OFF.

2. It depends on AC power supply come or gone.

3. This circuit is used when you are sleeping.

4. Easy to make

5. Cost is very low

6. Components are few.

7. Battery can’t over charge.

8. Overall efficiency is 78%.

9. Not you, only relay can do your work.

10. The circuit is a small project for all students.

Battery Charger Control Circuit

2011-07-07T02:08:00.003+06:00

Battery charger control circuit is very useful now-a-days. You need not follow on battery charging or disconnect from ac power for avoiding over charge. This circuit is used to charge battery when the battery voltage drops below the minimum voltage that you want to connect it to a charger. When the battery voltage reaches the maximum voltage you want the charger to be connected.

This circuit is shown in figure. Let your battery voltage is 15 volt. When Ei drops below 10.5 V, V0 goes negative, releasing the relay to its normally closed position. The relay’s normally closed (NC) contacts connect the charger to battery Ei. Diode D1 protects the transistor against excessive reverse bias when V0 = -Vsat. When the battery charges to 13.5 V, V0 switches to disconnect the charger. Diode D2 protects both op-amp and resistor against transients developed by the relay’s collapsing magnetic field.

Suppose that the application requires an inverting voltage level detector with hysteresis. That is V0 must go low when Ei goes above Vut and V0 must go high when Ei drops below Vlt. For this application, do not change the circuit or design procedure for the non-inverting voltage level detectors, simply add an inverting amplifier, or inverting comparator, to the output Vo.

Heat Sensor Circuit

2011-06-21T19:36:00.003+06:00

This is the simple heat sensor circuit. It can be used to control any device using heat sensor. In this circuit a thermistor and a resistance is connected in series. This arrangement makes a potential divider circuit.

Here the thermistor is Negative Temperature Coefficient type. So when the room temperature is increased its resistance decreases simultaneously and more current flows through the resistor and the thermistor. We find more voltage at the junction of the resistor and the thermistor.

Our thermistor resistance value is 110 ohms. Suppose the resistance value becomes 90 ohms after heating the 110 ohms thermistor. Then the voltage across one resistor of the voltage divider circuit equals the ratio of that resistor’s value and the sum of resistances of the voltage across the series combination. This is the concept of voltage divider.

The final output voltage of the voltage divider circuit is now applied to the npn transistor (BC548) through the base resistor (3.3K ohms). Here the emitter resistor is replaced with a zener diode. Emitter voltage is maintained at 4.7volt with the help of zener diode. This voltage is used to compare voltage. Transistor conducts when base voltage is greater than the emitter voltage. Transistor conducts if it gets more than 4.7volt of base voltage. Then the circuit is completed through buzzer and it gives sound.

Active FM Antenna Amplifier of FM Booster

2011-06-20T19:10:00.003+06:00

FM booster is one kind of a preamplifier which can be used to listen FM radio programs from distance FM stations clearly. The circuit comprises a common-emitter tuned RF preamplifier which tuned RF preamplifier wired around VHF/UHF transistor 2SC2570.

Serial	Parts Lists	Value
1	R1	27kΩ
2	R2	270Ω
3	R3	1kΩ
4	C1	5.6pF
5	C2	5.6pF
6	C3	1n
7	C4
8	C5	10pF
9	C6	0.1µF
10	VC1	22pF Trimmer capacitor
11	L1	1T FROM BOTTOM END
12	L2	3T, 20SWG 5mm DIA, AIR CORE
13	T1	2SC2570

Adjust input/ output trimmers (VC1/VC2) for maximum gain.

3 digits Digital Ammeter using Microcontroller

2011-06-16T07:31:00.003+06:00

Digital Ammeter is needed to do any kind of electronics circuit making. It is very much useful who is interested in electronics projects. Now-a-days there are many kind of digital or analog ammeter which are found in the market. But if you make such kind of digital meter then you have no no bounds happy.

The bellow circuit is digital Ammeter based on PIC16F684 and ACS712 current sensor. Here the measured ac/dc current will display on three digit 7-segment with resolution 100mA. In this project current sensor is ACS712ELCTR-30A-T . This circuit can measure the ac or dc current up to 30mA with 66mV/A output sensitivity.

The micro-controller PIC16F684 is used to read analog value from the ACS712 current sensor output and micro-controller convert to current and displaying on 7-segments display. For this circuit all 7-segment displays will be common anode type and it driven by PNP transistor BC557. Originally, this circuit is suitable for measuring DC current.

Remote Control Using the NE 555 and LM 567

2011-06-16T07:14:00.003+06:00

Remote control circuit consists of two parts, one is transmitter and the other is receiver. A simple diagram is schematic remote control. The transmitter circuit’s transmitter IC is controlled by NE555. Receiver circuit works by the signal emitted frequency which is emitted by that transmitter circuit. Transmitted signal frequency must be equal to the frequency decoder of the receiver circuit. The NE 555 generated frequency is same that receive frequency of IC LM 567.

The output frequency of the transmitter circuit is f,

f = 1.44/(Ra+2Rb)C

The resistor R1 is a receiver variable to facilitate the process of tuning. The system works well when the circuit is ready. The first step is tuning by way of the transmitter is turned on continuously, while the receiver R1 to set the value to be able to detect the signal transmitter. The second part is the receiver is controlled by LM 567. The following is a schematic drawing recipient.

f = 1 / (1.1 xR1xC1)

This frequency depends on the value of R₁ and C₁.

In the picture on top of each channel is designed with a different frequency. By considering the bandwidth of the frequency detection signal LM 567, inter-frequency channels should have a big enough difference, let’s try with a difference of 5 KHz.