1LAPTOP AUDIO AMPLIFIER
Usually, the audio output from a laptop’s built-in speakers is low. A power amplifier is required to get a high volume. Here is a simple circuit to amplify the laptop’s audio output.
The circuit is built around power amplifier IC LA 4440 (IC1) and a few other components. LA4440 is a dual channel audio power amplifier. It has low distortion over a wide range of low to high frequencies with good channel separation. Inbuilt dual channels enable it for stereo and bridge amplifier applications.
In dual mode LA4440 gives 6 watts per channel and in bridge mode 19- watt output. It has ripple rejection of 46 dB. The audio effect can be realised by using two 6-watt speakers. Connect pins 2, 6 and ground of IC1 to the stereo jack which is to be used with the laptop.
Assemble the circuit on a general-purpose PCB and enclose in a suitable cabinet. The circuit works off regulated 12V power supply. It is recommended to use audio input socket in the circuit board. Use a proper heat-sink for LA4440.
2Remote Control for Toy Car
Make any battery-operated toy car remote-controlled using this circuit. The circuit, consisting of an infrared transmitter-receiver pair, uses IR beam transmission to switch the toy car 'on' or 'off '. To operate the toy car, you need to hold the transmitter in your hand, keeping it pointed at the toy car which has the receiver fitted inside, and simply press a switch provided on the transmitter.
The transmitter works off 9V DC, while the receiver needs 6V DC. Fig. 1 shows the transmitter circuit. It is built around two BC558 transistors (T1 and T2), ,three BC548 transistors (T3, T4 and T5), IR LED1 and a few discrete components.
Fig. 1: Transmitter circuit
Fig. 2 shows the receiver circuit. It is built around IR receiver module TSOP1738, two BC548 transistors (T6 and T7) and a few discrete components. In the transmitter circuit, there are two astable multivibrators. The first, built around transistors T1 and T2, produces a frequency of about 1.2 kHz. The second, built around transistors T3 and T4, produces about 38 kHz. IR LED1 is used to transmit the 38kHz frequency.
3LASER COMMUNICATION SYSTEM
This laser communication system transmits sound or music signals through a laser beam. The intensity of the laser beam changes with the amplitude of the sound signal. The variation in the intensity of the laser beam is converted into a variation in the voltage level by using a calculator's solar panel. The voltage variation on the solar panel is amplified by a low-voltage audio power amplifier LM386 and reproduced by a speaker. The maximum output of audio amplifier LM386 is 1 watt, while its voltage gain is 20 to 200.
he circuit consists of a transmitter and a receiver. Both the transmitter and the receiver are built around IC LM386, powered by a 9V battery.
Fig. 1 shows the transmitter circuit. Here a laser diode (LD1) with maximum operating voltage of around 2.6V DC and maximum operating current of 45 mA is used to transmit the audio signal. The voltage divider network formed by R2, R3 and VR3 keeps the voltage as well as the current for the laser diode in the safe region.
Fig. 1: Transmitter circuit
In place of the laser diode, you can also use a laser pointer. Remove the battery from the laser pointer. Extend two wires from terminals of LD1 and connect them to the battery terminals of laser pointer. The spring inside the laser pointer is the negative terminal. The output power of the laser pointer is 5 mW. Take care while working with laser, as direct exposure to the laser beam can be hazardous to your eyes. Point the laser beam to the solar panel.
Potmeter VR1 (10-kilo-ohm) is used to change the level of the input audio signal. The audio input (Vin) is taken from the preamplifier output of the music system (CD player, DVD player, etc). Capacitor C2 and preset VR2 are used to vary the gain of the LM386.
Fig. 2 shows the receiver circuit. The audio signal transmitted by the laser diode (LD1) is received by the calculator's solar panel and amplified by IC2. The gain of the amplifier is fixed by capacitor C7. Preset VR4 is used to change the signal level from the solar panel. This signal is fed to input pin 3 of IC2 through coupling capacitor C5 so that the DC value from the solar panel can be eliminated. The amplified output from IC2 is fed to the speaker, which plays the music from the CD player connected at the input (Vin) of IC1.
Fig. 2: Receiver circuit
Assemble the transmitter and receiver circuits on separate PCBs and enclose in suitable cabinets. In the transmitter cabinet, fix two terminals for connecting the audio signal. Fix switch S1 on the front panel and the laser diode (LD1 or laser pointer) to the rear side of the cabinet. Keep the 9V battery inside the cabinet.
In the receiver cabinet, fix the calculator's solar panel to the rear side such that the transmitted beam directly falls on it. Fix switch S2 on the front panel and the speaker to the rear side. Keep the 9V battery inside the cabinet. Refer Figs 3 and 4 for the laser pointer and calculator's solar panel.
After assembling both the circuits, orient the laser diode (or laser pointer) such that the transmitted laser beam directly falls on the solar panel. Use shielded wires for connecting to audio input and solar panel to reduce noise pickup.
4TELEPHONE CALL RECORDER
Today telephone has become an integral part of our lives. It is the most widely used communication device in the world. Owing to its immense popularity and widespread use, there arises a need for call recording devices, which find application in call centres, stock broking firms, police, offices, homes, etc.
Fig. 1: Call recorder circuit
Here we are describing a call recorder that uses very few components. But in order to understand its working, one must first have the basic knowledge of standard telephone wiring and a stereo plug.
In India, landline telephones primarily use RJ11 wiring, which has two wires-tip and ring. While tip is the positive wire, ring is the negative one. And together they complete the telephone circuit. In a telephone line, voltage between tip and ring is around 48V DC when handset is on the cradle (idle line). In order to ring the phone for an incoming call, a 20Hz AC current of around 90V is superimposed over the DC voltage already present in the idle line.
The negative wire from the phone line goes to IN1, while the positive wire goes to IN2. Further, the negative wire from OUT1 and the positive wire from OUT2 are connected to the phone. All the resistors used are 0.25W carbon film resistors and all the capacitors used are rated for 250V or more. The negative terminal of 'To AUX IN' is connected to pin 1 of the stereo jack while the positive terminal is connected to pins 2 and 3 of the stereo jack. This stereo jack, in turn, is connected to the AUX IN of any recording device, such as computer, audio cassette player, CD player, DVD player, etc. Here we shall be connecting it to a computer.
When a call comes in, around 90V AC current at 20Hz is superimposed over the DC voltage already present in the idle line. This current is converted into DC by the diodes and fed to resistor R1, which reduces its magnitude and feeds it to LED1. The current is further reduced in magnitude by the resistor R2 and fed to the right and left channels of the stereo jack, which are connected to the AUX IN port of a computer.
Fig. 2: Pin configuration of stereo jack
Any audio recording software,such as AVS audio recorder (available at: http://www.avs4you.com/AVS-Audio-Recorder.aspx), Audacity audio recorder (http://audacity.sourceforge.net/), or audio recorder (http://www.audio-tool.net/audio_recorder_for_free.html), can be used to record the call. When a call comes in, one needs to launch the audio recording software and start recording.
For phone recording, simply connect the stereo jack to the AUX IN port of the PC. Install the audacity audio recorder (different versions are available for free for different operating systems at http://audacity.sourceforge.net/) on your PC. Run the executable audacity file. In the main window, you will find a drop-down box in the top right corner. From this box, select the AUX option. Now you are ready to record any call. As soon as a call comes in, press the record button found in the audacity main window and then pick up the telephone receiver and answer the call. Press the stop button once the call ends. Now go to the file menu and select the 'Export as WAV' option and save the file in a desired location.
You may change the value of resistor R2 if you want to change the output volume. you can use a variable resistor in series with R2 to vary the volume of the output. The recorded audio clip can be edited using different options in the audacity software.
Fig. 3: RJ connector
You can assemble the circuit on a general-purpose PCB and enclose it in a small cabinet. Use an RJ11 connector and stereo jack for connecting the telephone set and computer (for call recording). Telephone cords can be used to connect to the phone line and the circuit. Use of a shielded cable is recommended to reduce disturbances in the recording. These can also be reduced by increasing the value of R2 to about 15 kilo-ohms.
5DUO PHONE |
This simple circuit of a duophone allows you to access two telephone lines through one telephone set. Each telephone conversation will remain entirely separate unless you choose to combine the two lines through a conference switch. Its unique feature is a three-party conversation/conference facility.
The entire circuit is divided into three main sections-the ringer, hold and conferencing. The telephone set is connected to line 1 under normal conditions. The ringer is used for indicating a call on line 2 that is not connected to the telephone receiver. When you have a call on line 2, the ringer will buzz. The telephone receiver can then be connected to line 2 through the telephone changeover switch S4 to receive the call.
The ringer section is built around IC3 and its associated components. Its circuit uses IC 1240 to detect the ring signal and keeps the buzzer ringing for an incoming call on line 2. The supply voltage for the ringer is obtained from the phone line's AC ring (80V AC RMS) signal and is regulated inside the IC so that the noise on the line does not affect operation of the IC. The two-tone frequencies generated are switched by an internal oscillator in a fast sequence, which appear at the output amplifier and drive the piezo buzzer element directly.
The hold section is built around IC1 and IC2 . Switch S1 is used to hold line 1 and S2 is used to put line 2 on hold. Since one telephone set is used for two separate lines, provision is thus made to hold the first call while the telephone set is connected to make or receive the second call.
The circuit comprises two identical hold circuits, each with its own flashing LED to maintain the holding current. Each hold circuit has a timer LM555 (IC1 or IC2) connected as a free-running oscillator operating at a frequency of 2 Hz. The output pin 3 of each timer is used for driving an LED that flashes twice in a second. The hold circuit is powered by the telephone lines through manually-operated hold switches (S1 and S2). Resistors R2 and R6 are placed in the hold circuits to ensure that sufficient current is drawn from the telephone line to prevent a disconnection.
The conferencing section is built around the audio coupling transformer X1. Switch S3 enables three-way conversation through both the telephone lines. The transformer couples the audio signals from one telephone line to the other. At the same time, complete DC isolation is maintained between both the telephone lines. Capacitors C1 and C3 are used for preventing any DC from flowing into the transformer windings. Resistor R1 provides a holding current on line 1 when the telephone set is connected to line 2 during a conference call. Once the three-way conversation is established through the double-pole single-throw (DPST) switch S3, the hold circuits and flashing LED indicators are turned off. LED3, which gets illuminated by the holding current through R1, provides a visual indication of the conferencing.
The working of the circuit is simple. To check if the wiring of switch S4 is correct, connect the telephone set to line 1. Now lift up the handset and dial the number of line 2. the ringer would sound. Now disconnect line 1 and connect line 2 through switch S4. You would get the dial tone from line 2.
To check a conference call, you would need the help of two friends. First connect switch S4 to line 1 and make a call to friend 1. Now flip the DPST switch S3 to the 'on' position. This puts on hold friend 1 on line 1 and the conference LED3 lights up. Connect switch S4 to line 2 and dial friend 2. When the call on line 2 is answered, a three-way conversation can be made.
When the duophone is not in use, connect switch S4 to line 1. All other switches should be in the 'off' mode and all LEDs should be unlit. This permits the telephone ringer to be activated if a call comes on line 2. For making calls using line 1 or line 2, you can simply connect switch S4 to the desired line.
Assemble the circuit on a general purpose PCB and enclose it in a suitable cabinet. Fix the switches S1 through S4 on the front side of the cabinet. Also fix the LEDs on the front of the cabinet and the buzzer at the back of the cabinet. It would be better if you use telephone sockets for the telephone lines. Sockets are relatively inexpensive and save time when troubleshooting needs to be done. Use modular plugs to connect the circuit and the two telephone lines. By using such 'quick disconnect' plugs, you can easily remove the unit from the telephone lines. Check the polarity of the telephone lines with a multimeter and connect it to the circuit accordingly.
To check the circuit after completing the wiring, connect a 6V regulated power supply to line 1. When you switch S1 to the 'on' position, LED1 blinks at a rate of 2 Hz. If you flip switch S1 to the 'off 'position and switch S3 to the 'on' position, LED1 stops blinking and LED3 starts glowing, indicating that the conferencing facility is being used. Now disconnect line 1 from the 6V power supply, connect it to line 2 and flip switch S2 to the 'on' position. Now LED2 blinks at a rate of 2 Hz. Before connecting the circuit to the telephone lines, flip each hold switch to the 'off' position. Now your circuit is ready to be used.
The entire circuit is divided into three main sections-the ringer, hold and conferencing. The telephone set is connected to line 1 under normal conditions. The ringer is used for indicating a call on line 2 that is not connected to the telephone receiver. When you have a call on line 2, the ringer will buzz. The telephone receiver can then be connected to line 2 through the telephone changeover switch S4 to receive the call.
The ringer section is built around IC3 and its associated components. Its circuit uses IC 1240 to detect the ring signal and keeps the buzzer ringing for an incoming call on line 2. The supply voltage for the ringer is obtained from the phone line's AC ring (80V AC RMS) signal and is regulated inside the IC so that the noise on the line does not affect operation of the IC. The two-tone frequencies generated are switched by an internal oscillator in a fast sequence, which appear at the output amplifier and drive the piezo buzzer element directly.
The hold section is built around IC1 and IC2 . Switch S1 is used to hold line 1 and S2 is used to put line 2 on hold. Since one telephone set is used for two separate lines, provision is thus made to hold the first call while the telephone set is connected to make or receive the second call.
The circuit comprises two identical hold circuits, each with its own flashing LED to maintain the holding current. Each hold circuit has a timer LM555 (IC1 or IC2) connected as a free-running oscillator operating at a frequency of 2 Hz. The output pin 3 of each timer is used for driving an LED that flashes twice in a second. The hold circuit is powered by the telephone lines through manually-operated hold switches (S1 and S2). Resistors R2 and R6 are placed in the hold circuits to ensure that sufficient current is drawn from the telephone line to prevent a disconnection.
The conferencing section is built around the audio coupling transformer X1. Switch S3 enables three-way conversation through both the telephone lines. The transformer couples the audio signals from one telephone line to the other. At the same time, complete DC isolation is maintained between both the telephone lines. Capacitors C1 and C3 are used for preventing any DC from flowing into the transformer windings. Resistor R1 provides a holding current on line 1 when the telephone set is connected to line 2 during a conference call. Once the three-way conversation is established through the double-pole single-throw (DPST) switch S3, the hold circuits and flashing LED indicators are turned off. LED3, which gets illuminated by the holding current through R1, provides a visual indication of the conferencing.
The working of the circuit is simple. To check if the wiring of switch S4 is correct, connect the telephone set to line 1. Now lift up the handset and dial the number of line 2. the ringer would sound. Now disconnect line 1 and connect line 2 through switch S4. You would get the dial tone from line 2.
To check a conference call, you would need the help of two friends. First connect switch S4 to line 1 and make a call to friend 1. Now flip the DPST switch S3 to the 'on' position. This puts on hold friend 1 on line 1 and the conference LED3 lights up. Connect switch S4 to line 2 and dial friend 2. When the call on line 2 is answered, a three-way conversation can be made.
When the duophone is not in use, connect switch S4 to line 1. All other switches should be in the 'off' mode and all LEDs should be unlit. This permits the telephone ringer to be activated if a call comes on line 2. For making calls using line 1 or line 2, you can simply connect switch S4 to the desired line.
Assemble the circuit on a general purpose PCB and enclose it in a suitable cabinet. Fix the switches S1 through S4 on the front side of the cabinet. Also fix the LEDs on the front of the cabinet and the buzzer at the back of the cabinet. It would be better if you use telephone sockets for the telephone lines. Sockets are relatively inexpensive and save time when troubleshooting needs to be done. Use modular plugs to connect the circuit and the two telephone lines. By using such 'quick disconnect' plugs, you can easily remove the unit from the telephone lines. Check the polarity of the telephone lines with a multimeter and connect it to the circuit accordingly.
To check the circuit after completing the wiring, connect a 6V regulated power supply to line 1. When you switch S1 to the 'on' position, LED1 blinks at a rate of 2 Hz. If you flip switch S1 to the 'off 'position and switch S3 to the 'on' position, LED1 stops blinking and LED3 starts glowing, indicating that the conferencing facility is being used. Now disconnect line 1 from the 6V power supply, connect it to line 2 and flip switch S2 to the 'on' position. Now LED2 blinks at a rate of 2 Hz. Before connecting the circuit to the telephone lines, flip each hold switch to the 'off' position. Now your circuit is ready to be used.
6CAR-REVERSING HORN WITH FLASHER
Here is a simple circuit that starts playing the car horn whenever your car is in reverse gear. The circuit (refer Fig. 1) employs dual timer NE556 to generate the sound. One of the timers is wired as an astable multivibrator to generate the tone and the other is wired as a monostable multivibrator.
Fig. 1: Car reverse horn
Working of the circuit is simple. When the car is in reverse gear, reverse-gear switch S1 of the car gets shorted and the monostable timer triggers to give a high output. As a result, the junction of diodes D1 and D2 goes high for a few seconds depending on the time period developed through resistor R4 and capacitor C4. At this point, the astable multivibrator is enabled to start oscillating. The output of the astable multivibrator is fed to the speaker through capacitor C6. The speaker, in turn, produces sound until the output of the monostable is high.
When the junction of diodes D1 and D2 is low, the astable multivibrator is disabled to stop oscillating. The output of the astable multivibrator is fed to the speaker through capacitor C6. The speaker, in turn, does not produce sound.
Assemble the circuit on a general-purpose PCB and enclose in a suitable cabinet. Connect the circuit to the car reverse switch through two wires such that S1 shorts when the car gear is reversed and is open otherwise. To power the circuit, use the car battery.
The flasher circuit (shown in Fig. 2) is built around timer NE555, which is wired as an astable multivibrator that outputs square wave at its pin 3. A 10W auto bulb is used for flasher. The flashing rate of the bulb is decided by preset VR1.
Fig. 2: Flasher circuit
Assemble the circuit on a general-purpose PCB and enclose in a suitable cabinet. The flasher bulb can be mounted at the car's rear side in a reflector or a narrow painted suitable enclosure. 7SKIN RENSPONSE METER
Human skin offers some resistance to current and voltage. This resistance changes with the emotional state of the body. The circuit proposed here measures changes in your skin resistance following changes in your mental state.
In the relaxed state, the resistance offered by the skin is as high as 2 mega-ohms or more, which reduces to 500 kilo-ohms or less when the emotional stress is too high. The reduction in skin resistance is related to increased blood flow and permeability followed by the physiological changes during high stress. This increases the electrical conductivity of the skin.This circuit is useful to monitor the skin's response to relaxation techniques. It is very sensitive and shows response during a sudden moment of stress. Even a deep sigh will give response in the circuit.
The circuit uses a sensitive amplifier to sense variations in the skin resistance. IC CA3140 (IC1) is designed as a resistance-to-voltage converter that outputs varying voltage based on the skin's conductivity. It is wired as an inverting amplifier to generate constant current to skin in order to measure the skin resistance.
IC CA3140 is a 4.5MHz BiMOS operational amplifier with MOSFET inputs and bipolar output. The gate-protected inputs have high impedance and can sense current as low as 10 pA. This device is ideal to sense small currents in low-input-current applications.
The inverting input (pin 2) of IC1 is connected to ground (through preset VR1) and one of the touch plates, while the non-inverting input (pin 3) is grounded directly. The output from IC1 passes through current-limiting resistor R1 to the second touch plate. R1 act as a feedback resistor along with the skin when the touch plates make contact with the skin. So the gain of IC1 depends on the feedback provided by R1 and the skin.
In the inverting mode of IC1, a positive input voltage to its pin 2 through the feedback network makes its output low. If the skin offers very high resistance in the relaxed state, input voltage to pin 2 reduces and the output remains high. Thus the gain of IC1 varies depending on the current passing through the skin, which, in turn, depends on the skin response and emotional state.
In the standby state, touch plates are free. As there is no feedback to IC1, it gives a high output (around 6 volts), which is indicated by shifting of the meter to right side.When the touch plates are shorted by the skin, the feedback circuit completes and the output voltage reduces to 4 volts or less depending on the resistance of the skin. Since the feedback network has a fixed resistor (R1) and VR1 is set to a fixed resistance value, the current flowing through it depends only on the resistance of the skin. The output from IC1 is displayed on a sensitive moving coil meter (VU meter). By varying preset VR2, you can adjust the sensitivity of the meter.
For easy visual observation, an LED display is also included. IC LM3915 (IC2) is used to give a logarithmic display through LED indications. It can sink current from pin 18 to pin 10 with each increment of 125 millivolts at its input pin 5. Using VR3 you can adjust the input voltage of IC2, while using VR4 you can control the brightness of the LEDs.
In practice, the circuit provides both meter reading and LED indications. If the LED display is not needed, IC2 can be omitted.
Assemble the circuit on a general-purpose PCB and enclose in a suitable cabinet with touch pads glued on the top, 5-10 mm apart. Touch pads can be any type of conducting plates, such as aluminium or copper plates, having dimensions of 1XC1 cm2. The moving coil meter can be a small VU meter with 1-kilo-ohm coil resistance and 0-10 digit reading.
After assembling the circuit, adjust the presets such that IC1 outputs around 6 volts. None of the LEDs (LED1 through LED3) glows in this position with the touch plates open.
Now gently touch the touch plates with your middle finger. Maintain the finger still allowing one minute to bond with the pads and keep your body relaxed. Adjust VR3 until the green LED (LED1) lights up and the meter shows full deflection. Adjust VR2 to get maximum deflection of the meter. This indicates normal resistance of the skin, provided the body is fully relaxed.
If you are stressed or have ill feeling, skin resistance decreases and the blue LED lights up followed by the red LED along with a deflection of the meter towards the lower side. In short, the red LED and zero meter reading indicate you are stressed, and the green LED and high meter reading indicate you are relaxed. Practise some relaxation technique and observe how much your body is relaxed.
8USB POWER SOCKET
Today, almost all computers contain logic blocks for implementing a USB port. A USB port, in practice, is capable of delivering more than 100 mA of continuous current at 5V to the peripherals that are connected to the bus. So a USB port can be used, without any trouble, for powering 5V DC operated tiny electronic gadgets.
Nowadays, many handheld devices (for instance, portable reading lamps) utilise this facility of the USB port to recharge their built-in battery pack with the help of an internalcircuitry. Usually 5V DC, 100mA current is required to satisfy the input power demand.
Fig. 1 shows the circuit of a versatile USB power socket that safely converts the 12V battery voltage into stable 5V. This circuit makes it possible to power/recharge any USB power-operated device, using in-dash board cigar lighter socket of your car.
Fig. 1: Circuit of USB power socket
The DC supply available from the cigar lighter socket is fed to an adjustable, three-pin regulator LM317L (IC1). Capacitor C1 buffers any disorder in the input supply. Resistors R1 and R2 regulate the output of IC1 to steady 5V, which is available at the 'A' type female USB socket. Red LED1 indicates the output status and zener diode ZD1 acts as a protector against high voltage.
Assemble the circuit on a general-purpose PCB and enclose in a slim plastic cabinet along with the indicator and USB socket. While wiring the USB outlet, ensure correct polarity of the supply. For interconnection between the cigar plug pin and the device, use a long coil cord as shown in Fig. 2. Pin configuration of LM317L is shown in Fig. 3.
Fig. 2: Interconnection of cigar plug and USB power socket using a coil cord
Fig. 3: Pin configuration of LM317L (To-92 package)
Nowadays, many handheld devices (for instance, portable reading lamps) utilise this facility of the USB port to recharge their built-in battery pack with the help of an internalcircuitry. Usually 5V DC, 100mA current is required to satisfy the input power demand.
Fig. 1 shows the circuit of a versatile USB power socket that safely converts the 12V battery voltage into stable 5V. This circuit makes it possible to power/recharge any USB power-operated device, using in-dash board cigar lighter socket of your car.
Fig. 1: Circuit of USB power socket
The DC supply available from the cigar lighter socket is fed to an adjustable, three-pin regulator LM317L (IC1). Capacitor C1 buffers any disorder in the input supply. Resistors R1 and R2 regulate the output of IC1 to steady 5V, which is available at the 'A' type female USB socket. Red LED1 indicates the output status and zener diode ZD1 acts as a protector against high voltage.
Assemble the circuit on a general-purpose PCB and enclose in a slim plastic cabinet along with the indicator and USB socket. While wiring the USB outlet, ensure correct polarity of the supply. For interconnection between the cigar plug pin and the device, use a long coil cord as shown in Fig. 2. Pin configuration of LM317L is shown in Fig. 3.
Fig. 2: Interconnection of cigar plug and USB power socket using a coil cord
Fig. 3: Pin configuration of LM317L (To-92 package)
9ELECTRONIC BICYCLE LOCK
The electronic bicycle lock described here is a worthwhile alternative for bicycle owners who want to make their bicycles 'intelligent' at reasonable cost. One of the benefits of building it yourself is that the circuit can be used for virtually any make of bicycles.
In the circuit, input jacks J1 and J2 are two standard RCA sockets. A home-made security loop can be used to link these two input points. Around 50cm long, standard 14/36 flexible wire with one RCA plug per end is enough for the security loop.
Fig. 1 shows the circuit of the electronic bicycle lock. It is powered by a compact 9V battery (6F22). Key lock switch S1 and smoothing capacitor C2 are used for connecting the power supply. A connected loop cannot activate IC1 and therefore the speaker does not sound. When the loop is broken, zener diode ZD1 (3.1V) receives operating power supply through resistor R2 to enable tone generator UM3561 (IC1). IC1 remains enabled until power to the circuit is turned off using switch S1 or the loop is re-plugged through J1 and J2.
Fig. 1: Circuit of electronic bicycle lock
Assemble the circuit on a general-purpose PCB and house in a small tin-plate enclosure. Fit the system key lock switch (S1) on the front side of the enclosure as shown in Fig. 2. Place RCA sockets (J1 and J2) at appropriate positions. Now, mount the finished unit in place of your existing lock (as shown in Fig. 3) by using suitable clamps and screws.
Fig. 2: Lock box
In the circuit, input jacks J1 and J2 are two standard RCA sockets. A home-made security loop can be used to link these two input points. Around 50cm long, standard 14/36 flexible wire with one RCA plug per end is enough for the security loop.
Fig. 1 shows the circuit of the electronic bicycle lock. It is powered by a compact 9V battery (6F22). Key lock switch S1 and smoothing capacitor C2 are used for connecting the power supply. A connected loop cannot activate IC1 and therefore the speaker does not sound. When the loop is broken, zener diode ZD1 (3.1V) receives operating power supply through resistor R2 to enable tone generator UM3561 (IC1). IC1 remains enabled until power to the circuit is turned off using switch S1 or the loop is re-plugged through J1 and J2.
Fig. 1: Circuit of electronic bicycle lock
Assemble the circuit on a general-purpose PCB and house in a small tin-plate enclosure. Fit the system key lock switch (S1) on the front side of the enclosure as shown in Fig. 2. Place RCA sockets (J1 and J2) at appropriate positions. Now, mount the finished unit in place of your existing lock (as shown in Fig. 3) by using suitable clamps and screws.
Fig. 2: Lock box
Fig. 3: Lock fitted on the bicycle
10REMOTE-OPERATED MASTER SWITCH
Generally, a bedside master switch is used to switch on lamps both indoors and outdoors when there is a threat of intruder. This circuit can be used to activate the master switch from the bed without searching for the switch in darkness. It can be activated by the TV remote handset. The security lamps glow for three minutes and then turn off. The circuit is sensitive and can be activated from a distance of up to 25 metres.
IR receiver module TSOP 1738 (IRX1) is used to sense the pulsed 38kHz IR rays from the TV remote handset. The IR receiver module has a PIN photodiode and a preamplifier enclosed in an IR filter epoxy case. Its open-collector output is 5 volts at 5mA current in the standby mode.
In the standby mode, no IR rays from the remote handset fall on the IR receiver, so its output pin 3 remains high and LED1 doesn't glow. Through esistor R2, the base of transistor T1 remains high and it does not conduct. As a result, the voltage at pin 3 of IC CA3130 (IC1) remains low. The potential divider comprising resistors R4 and R5 maintains half of 5.1V at pin 2 of IC1. In brief, the voltage at pin 2 of IC1 is higher than at pin 3 and its output remains low. LED2 remains 'off'and transistor T2 does not conduct. Relay RL1 remains de-energised and, as a result, security lamps (both indoors and outdoors) remain switched off.
When you press any key of the remote TV handset, IR rays fall on the receiver (IRX1) and its output goes low. LED1 flashes in sync with pulsation of the IR rays. At the same time, transistor T1 (BC558) conducts to take pin 3 of IC1 high. IC1 is used as a comparator with timer action.
When transistor T1 conducts, pin 3 of IC1 gets a higher voltage than pin 2 making the output of IC1 high. Meanwhile, capacitor C4 charges to full voltage and keeps pin 3 high for a few minutes even after T1 is non-conducting. Resistor R3 provides discharge path for capacitor C4, which decides the time period for which the output of comparator IC1 should remain high
The high output of IC1 energises relay RL1 through relay-driver transistor T2. Thus the load, i.e., security lamps, turn on for three to four minutes. LED2 glows to indicate activation of the relay as well as switching 'on' of the security lights. Connect a single-pole, single-throw 'on'/'off'switch (MS) to activate the security lamps manually when required.
Zener diode ZD1 provides 5.1V DC for safe operation of the IR receiver and associated circuit. Power for the circuit is derived from a step-down transformer (X1) and a bridge rectifier comprising diodes D1 through D4. Smoothing capacitor C1 removes ripples, if any, from the power supply.
Assemble the circuit on a general-purpose PCB and enclose in a suitable cabinet. Drill holes on the front panel for mounting the IR sensor and LEDs. Connect the master switch between the normally-open (N/O) contact and pole of relay RL1 so that the master switch can be used when needed. The relay contacts rating should be more than 4A. Mount the unit near the master switch using minimal wiring.
IR receiver module TSOP 1738 (IRX1) is used to sense the pulsed 38kHz IR rays from the TV remote handset. The IR receiver module has a PIN photodiode and a preamplifier enclosed in an IR filter epoxy case. Its open-collector output is 5 volts at 5mA current in the standby mode.
In the standby mode, no IR rays from the remote handset fall on the IR receiver, so its output pin 3 remains high and LED1 doesn't glow. Through esistor R2, the base of transistor T1 remains high and it does not conduct. As a result, the voltage at pin 3 of IC CA3130 (IC1) remains low. The potential divider comprising resistors R4 and R5 maintains half of 5.1V at pin 2 of IC1. In brief, the voltage at pin 2 of IC1 is higher than at pin 3 and its output remains low. LED2 remains 'off'and transistor T2 does not conduct. Relay RL1 remains de-energised and, as a result, security lamps (both indoors and outdoors) remain switched off.
When you press any key of the remote TV handset, IR rays fall on the receiver (IRX1) and its output goes low. LED1 flashes in sync with pulsation of the IR rays. At the same time, transistor T1 (BC558) conducts to take pin 3 of IC1 high. IC1 is used as a comparator with timer action.
When transistor T1 conducts, pin 3 of IC1 gets a higher voltage than pin 2 making the output of IC1 high. Meanwhile, capacitor C4 charges to full voltage and keeps pin 3 high for a few minutes even after T1 is non-conducting. Resistor R3 provides discharge path for capacitor C4, which decides the time period for which the output of comparator IC1 should remain high
The high output of IC1 energises relay RL1 through relay-driver transistor T2. Thus the load, i.e., security lamps, turn on for three to four minutes. LED2 glows to indicate activation of the relay as well as switching 'on' of the security lights. Connect a single-pole, single-throw 'on'/'off'switch (MS) to activate the security lamps manually when required.
Zener diode ZD1 provides 5.1V DC for safe operation of the IR receiver and associated circuit. Power for the circuit is derived from a step-down transformer (X1) and a bridge rectifier comprising diodes D1 through D4. Smoothing capacitor C1 removes ripples, if any, from the power supply.
Assemble the circuit on a general-purpose PCB and enclose in a suitable cabinet. Drill holes on the front panel for mounting the IR sensor and LEDs. Connect the master switch between the normally-open (N/O) contact and pole of relay RL1 so that the master switch can be used when needed. The relay contacts rating should be more than 4A. Mount the unit near the master switch using minimal wiring.
CONTINUE....................................................................
