This is a circuit of a resistance checker which provides an audible assessment of the resistance. It tests open circuit and short circuit conditions, and checks resistance between two points.
Automatic Sprinkler Control System circuit is designed as an expansion module to automatic sprinkler systems. It can be fitted in place of existing solenoid in the system to add new sprinkler wires without having to update the controller or run new wiring.
This circuit provides solution for the guitar players who use guitar pedals. It reduces the wiring and provides all amplification and effects on a PCB. It can be used to design pedals for upto five effects.
It is a circuit for a portable electric lamp and LED flasher. It contains a bulb and 9 LEDs. The bulb and LEDs glow alternately, depending on the frequency set in the circuit.
It is a circuit for designing an electronic metronome which can generate regular beats in the range of 40 to 200 beats per minute. The tempo and the pitch can be changed by using the knobs in the circuit.
This is a system based on PIR motion detector module BS1600 (or BS1700) that can be used for security or corridor lighting in power-saving mode. It contains a CFL that glows when it detects motion. When there is no motion, it glows for ten seconds, remains turned off for thirty seconds and then lights up again.
This tester is primarily meant to test bipolar transistors. It can indicate the type of the transistor as well as identify its base, collector and emitter pins
This is a circuit for a computerised telegraph which can transmit telegraph messages. The data entered through keyboard is converted into Morse code into computer using the Pascal program code given here. Then, this signal is transmitted in the form of a FM signal that can be received by any receiver tuned to the frequency of the signal being transmitted.
This is a circuit for a phototransistor detector based lock system. The system takes input in the form of punched cards that may have holes in any location corresponding to photo transistors. When a correct match is found in the lock depending upon the combination of the holes, a relay is driven and a tone is generated.
This is a circuit for a security system that can detect movement of any intruder through a transducer and activate any security device through a relay.
This is a circuit that can be used along with a computer to record calls to a telephone. The telephone can be connected to the circuit, which in turn, can be connected to the computer. A software such as Audacity Audio Recorder records the call.
This circuit for a fire alarm has a piezo sensor that detects the temperature in the room. It sets off an alarm if the temperature increases by more than 10 C. Then, a solenoid pump connected to the circuit starts operating which can be used to spray foam or water on fire.
This is a circuit to access two telephone lines through one telephone set. The conversations will remain independent on both lines unless they are combined with the conference switch on the circuit.
It is a circuit for triple power supply that can be used in laboratories or by hobbyists. It gives the option for three power supplies. One for variable voltage,one for +12 V and +5 volt and one for -12 V and -5 V.
This is a circuit for an automated alarm system that consists of a control unit and a sound alarm section. There are two sound alarm circuits here that produce bird-chirping sound and British police siren sound respectively. Any of the sound alarm sections can be used along with the control unit to make an alarm circuit with desired alarm sound.
This is a circuit for a traffic controller that uses three 15 W bulbs as the red, amber and green lights. It can also be used to teach traffic rules to children.
This circuit protects three-phase appliances from failure of any of the phases. It disconnects the power supply through the contactor and automatically restores the three-phase supply to the appliance after a time delay when all the phases are available.
This is a circuit for a bicycle signalling unit that can be used as a bicycle indicator. It contains two set of LEDs, one set for showing the right turn of bicycle and the other for left turn. It also has an emergency mode in which both the left and right indicators starts working simultaneously. It also has steady glow LEDs that indicate the working mode of the circuit.
This circuit of aquatic probe contains a signal diode that is used to monitor the temperature of water and indicate the rise in temperature through audio-visual indicators.
This is a low cost hearing aid circuit. Its sensitivity is less than that of commercial hearing aids. The circuit has two cascaded LA4537M ICs that give it fair sensitivity and reception range.
Glow plugs are used to heat the air inside a diesel engine so that the engine starts quickly. The Glow Plug Controller circuit heats the air inside the engine for about 25 seconds. When the circuit is started, a red LED glows to indicate the heating process. After a while green LED glows, followed a short beep of buzzer to indicate the engine is ready for starting.
This is a circuit for water alarm unit that can produce an alarm sound in the loudspeaker when water starts flowing through the tap. It uses a self made water sensor connected to 555 to detect the flow of water. Then a signal is sent to loudspeaker when water starts flowing in the tap which starts the alarm.
This is a circuit for a mobile transmission detector which can detect use of a mobile phone within the range of 1.5 metres. Whenever usage of mobile phone is detected such as calling or texting a beep alarm starts sounding and a led blinks.
This is a circuit for an emergency light that uses white LEDs for illumination. It consists of a charging circuit that charges the battery when main supply is on and automatically stops charging when battery is fully charged. It turns on automatically when main supply fails and turns off when main supply is back.
This low-cost circuit sounds an alarm when there someone knocks on the door. It consists of a piezoelectric element plate fixed at the centre of the door wing by using cellotape.
This circuit provides both +9V as well as -9V supply from a single 9V battery. It consists of timer 555 IC, negative-voltage regulator IC and a few discrete components.
This simple timer can be set to run for different time settings ranging from 30 seconds to 4.5 minutes. Also, a musical note is played at the end of the set time.
This circuit is designed to switch on/off any home or industrial appliance by using the TV/DVD remote controller. The circuit can be operated up to a distance of 5-10 metres depending on the remote used.
This is a circuit to test the CCFL (Compact cold cathode fluorescent lamp) tube in a LCD backlight unit, which may help the hardware technician to speed up his work. This basic
circuit (go/no go test) is portable, 6V battery operated and can be used to test almost all types of LCD backlight CCFL tubes.
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 '.
This laser communication system transmits sound or music signals through a laser beam. It consists of a laser diode transmitter and a solar panel receiver.
This circuit gives a visual indication of whether a telephone line is in use or not, helping two or more people sharing the line to avoid interrupting each other's calls. As the circuit connects in parallel with the telephone line, it can also detect phone tapping/misuse attempts.
Using this system, you can control your IR remote-controlled home appliances like DVD player and air-conditioner from another room without the hassle of running extra cables between the two rooms.
The system wirelessly sends infrared signals from one room to another.
This alarm circuit can be used to warn against trespass or unauthorised access in your premises. Its range can be extended further to protect the perimeter of a building from intrusion by using a cascade arrangement of multiple alarms.
This AC mains-operated bistable switch turns on or turns off a device using a miniature neon lamp and a few discrete components. This switch can be used for control panels, appliances and lighting controls.
This electronic lock for domestic use opens only when you
connect the right combination of five switches. There are twelve switches in total. If you connect a wrong combination, the lock remains closed. At night, flip a switch on to enable the torch.
This is a simple call bell circuit that displays a welcome message when somebody presses the call bell switch momentarily. The alphanumeric display can be fitted near the call bell switch.
It is an circuit which can generate wavelengths in the infrared region of the spectrum. It can be used with security cameras to design a security system which can throw infrared light which is not visible to human eye so as to capture movements in dark.
This circuit is used to convert an ordinary docking station into a smart electronic laptop docking station equipped with anti theft alarm. It features an optosensor. When someone tries to remove the laptop from the docking station the alarm will beep and an LED will glow.
This is a circuit for a guitar preamplifier that can capture mechanical vibrations (any standard guitar pickup) and then convert them into an electrical signal. The signal is then amplified by an audio amplifier.
The circuit described here can light a lamp from zero intensity to maximum intensity in a specified time set by user. The brightness is controlled by a continuously running ramp voltage generated by timer 555.
This is a circuit for an low cost pump controller which automates the filling of water in a tank. When the water level falls below a certain low point, the circuit switches on the pump which remains on till the water level reaches a high point. The low and high points are pre-set by the user.
This is a circuit that acts as a UPS for cordless phones so that they can work even in case of a power failure. When the supply is on the circuit charges the battery of UPS and in case of power failure the circuit supplies power to cordless phone from battery.
This is a circuit for a digital dice with numeric display that generates random numbers from 1 to 6 and displays them on a 7-segment LCD. The circuit can be modified to increase the range from 1 to 9.
This is a circuit for a electronic stop watch that can count up to 100 seconds with a resolution of 0.01 seconds or up to 1000 seconds with a resolution of 0.1 seconds.
This is a circuit for an intelligent switch that uses a photo transistor to detect day or night time and switches on an emergency light when it is dark in case of power failure.
This is a circuit for a low current high voltage power supply that can provide high output voltage. It has been implemented by using a combination of silicon diodes and zener diode.
This is a circuit for a color sensor which uses three LDRs to detect the color of object placed in front of it and indicates the same by glowing a corresponding color LED among 8 LEDs.
This circuit can test zener diodes with a breakdown voltage up to 120 volts. It takes only 6 volts as power supply and consumes less than 8 mA current.
This is a circuit for an automatic room power controller that consists of two LDRs. The LDRs sense the arrival of a person into the room and switch on the lights. It is an intelligent circuit that takes feedback from both LDRs to sense the persons coming inside the room.
This is a circuit for a smart phone light that uses a LDR that judges whether its day or night. If LDR detects night then a lamp is switched on when the telephone rings. The circuit takes power from the telephone line itself.
This is a circuit that can control up to four switches through clapping twice. The first clap takes the system out of standby mode while the second clap turns on or off the corresponding switch.
This circuit converts CD ROM drive in computers into a standalone audio CD player by just connecting power supply options to CD ROM and interconnecting it to either a tape deck or an audio amplifier.
This circuit uses parallel port of a computer for data input from binary counters. This data is used for measuring time and calculating the frequency of the signal.
This is a circuit of direct-conversion receiver that can be used to listen to amateur radio QSO signals in CW as well as in SSB mode in the 40-metre band.
This is a circuit for a digital switching system that can be used to control 16 devices with the help of two push to on switches. A master counter is used to select any of the device and an LED indicates the selected device.
This circuit can detect magnetic fields nearby through a reed switch. Whenever a magnetic field is detected, reed switch gets closed and a relay is energised in the circuit that can be used for various purposes.
This circuit can be used either as a sleep switch or as a wake timer. It provides a dual display for showing units and tens places of time in minutes or seconds format.
This is a circuit for a cordless phone backup unit that can be used to provide power supply to cordless phone at the time of main supply failure. A green LED indicates the presence of main supply and the circuit charges a rechargeable battery and puts the supply to cordless on battery in case of power failure.
This is a circuit that uses the printer port of a PC to interface it with a circuit and then by using the software provided electrical appliances can be controlled.
This is a circuit for a self switch power supply that can provide voltage in the range of 3.7 V to 8.7 V and turns itself off when no load is connected to it.
This circuit saves electrical appliances from damage in case of sudden tripping and resumption of power supply. It does so by switching off the main supply to the load which can only be resumed manually. The circuit does not work in the case of power fluctuations of the order of 1 millisecond to 5 milliseconds due to use of a large value capacitor.
This is a circuit for a telephone call meter designed with a calculator and chip on board. The calculator enables conversion of STD/ISD calls to local call equivalents and always displays current local call-meter reading.
This is a circuit that maintains secrecy of a telephone in a parallel telephone line where two telephones are connected to a same line by using a DPDT toggle switch so that the conversation can be active on only one line at a moment.
This is a circuit for a power supply failure alarm. It requires no separate supply for itself. It uses a capacitor to store enough charge for the alarm to sound for about one minute in case of a power failure.
This is a circuit for a low cost PCO billing meter that counts the number of pulses during a certain call and displays the corresponding number of rupees charged on a calculator according to a pre defined pulse rate by user.
This is a circuit for telephone intercom cum line changeover circuit that can be used to connect two telephones in parallel and also as a 2 line intercom using switches and a ring tone sensing circuit.
This is a circuit for an automatic speed controller for fans and coolers that can regulate speed of a fan during operation automatically. The fan is run at full speed for a predetermined time. The speed is decreased to medium after some time, and to slow later on. After a period of about eight hours, the fan/ cooler is switched off.
This is a circuit for a digital mains voltage indicator that displays main voltage in the form of a LED bar graph with 16 LEDs. The first LED indicates voltage level at 50 V and the 16th LED shows voltage level for 280 V.
This is a circuit that automates relay operation for electrical appliances and cuts off the power supply whenever the voltage varies outside the voltage range of 160 V to 270 V.
It is a circuit that implements an electronics dice using the random number generation capabilities of an AT89C2051 microcontroller. A random LED lights up in the panel of seven LEDs.
This circuit reminds you of all the important tasks that are due on a specific day every week. It can flash an LED on a particular day of week. It also has a buzzer that can be turned on manually through a switch, if beeping is required along with flashing for reminder.
This is a circuit for a logic probe that can test CMOS and TTL logic circuit and indicate their status by using combinations of red, green, yellow LEDs and a buzzer.
This circuit implements the concept of emergency light through relays. The circuit lights up LEDs in case of power failure and charges the batteries otherwise.
This is a circuit that switches off the supply to electrical appliances when there is any failure in power supply. It is based on transistors and triac and doesn't draw any power when the load is off.
This circuit can be used for either amplitude modulation (AM) or CW operation at 7 MHz by simply keeping a switch on or off for choosing any one between them.
This is a circuit for a water level indicator with an alarm. It consists of twelve levels. The circuit sounds an alarm when the water is below the lowest level or is higher than the topmost level. Also it contains LEDs for each corresponding level to show the current status of water in tank.
This is a circuit for an AC mains voltage detector that has an insulated sensing probe of length between 5 cm to 10 cm. When this sensing probe is taken in vicinity of AC mains the numbers in the display change repeatedly from 0 to 9 if it detects AC. If AC is not detected any random number is shown on the display.
This is a ringing circuit for telephones that uses a LED and an audio ringer IC to work as an extra ringing circuit which draws its power from telephone line.
This is a circuit for water level controller based on transistors and relays. The circuit automatically switches on the pump when water is low in the tank and switches the pump off when water reaches a predetermined mark. It also prevents dry run of the pump in case water gets below a suction level in underground tank.
This circuit contains 172 LEDs that are used to display Happy new year 2004 word by word for one second each and then displaying the whole message for four seconds.
This is a circuit for a digital audio video input selector that can add four audio video input to any standard colour television using a decade counter. A switch selects the number of the audio video input among the four that will be connected to TV.
It is a circuit that can check the status of a fuse. It has got a bi-coloured LED which turns to green if the fuse is fine and turns to red if the fuse is blown up. Modifications can be made for a buzzer to sound in case of fuse gets blown.
It is a circuit for testing of remote control transmitters. It contains a LED and buzzer who blink and beep respectively at the same rate of the incoming signal.
It is a circuit that indicates the level of water in a tank (low,half or full) on a 7-segment display. It uses a buzzer to alert the user about water overflowing from the tank.
This is a circuit for a home security system that sets off an alarm when someone interrupts a laser beam that continuously falls on LDR of the circuit. A combination of 6 plain mirrors is used to direct the laser beam around the house to form a net.
This circuit can be used to automate electrical light sources. It takes input in terms of a light dependent resistor (LDR) that can turn on the sources at night and turn them off during daytime. The circuit can be used for streetlights,
tubelights or any other home electrical system that needs to be automated.
In this circuit a piezobuzzer beeps after a fixed interval. If the timer is reset then it will beep again after the same time interval. If the timer is not reset then the circuit switches off the lights and fans in the room.
This circuit is designed to provide short circuit protection to a main circuit to which it is connected. It features two LEDs - a red one to indicate a short circuit and a green one to show normal working. When this additional circuitry is shorted by excess voltage red LED starts glowing and green starts glowing when the short is removed.
This is a circuit for a logic probe that can be used for analysing and troubleshooting of the logic states for TTL digital devices. It has two LEDs that represent high logical level (green) and low logic level (red).
This is a simple but inexpensive inverter for using a small soldering iron (25W, 35W, etc) in the absence of mains supply. It uses eight transistors and a few resistors and capacitors.
This is a circuit for a multitone siren that can produce sounds in five different audio tones. It is useful for burglar alarms, reverse horns etc., and is much more ear-catching than a single-tone siren.
This is a circuit for a battery charger with protection for overcharge, short circuit and deep-discharge. It can charge 6V, 9V and 12V batteries. The charging current is one tenth of the batteries rating.
This is a circuit for a liquid level alarm. A sensor can be placed in the liquid tank. A beeping tone is generated from the speaker when the tank is full.
This is a circuit for a light fitted in a generator room. The circuit can turn on the lights in the generator room automatically at night, and switch them off during daytime. Night and day are determined by using a light dependent resistor. An optional battery charger circuit can be connected to any external battery or battery in generator.
This is a circuit that measures changes in the skin resistance and shows the relaxation level of your mind. Blinking of red LED with low reading in the meter indicates a high level of stress. Blinking of the green LED, along with high reading on the meter represents a calm state of mind. Blue led is used to show human contact.
This is a circuit for a electronic bicycle lock. It sounds a buzzer when the loop of the bicycle lock is broken. The buzzer can only be turned off by resetting the key switch.
This is a circuit for a photovoltaic module that uses a solar panel to recharge a lead-acid battery. An additional circuit with an LED lamp is also present that can be powered either by Ni-Cd batteries or rechargeable batteries.
This is a circuit that can convert the USB socket of a PC into a power socket. This power socket will deliver 5 V dc and 100 mA current which can be used for 5 V electronic portable devices. A cigar plug pin can also be connected with USB.
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.
This circuit thwarts theft attempts by turning on the lights in certain areas of the house at around 1 am by getting the desired time delay from a CMOS IC CD4060. The circuit is reset by using an LDR.
This is an automatic door opener circuit that operates using a LASER diode. Whenever someone interrupts the laser beam the relay starts the door motor and the door is opened.
These are two separate circuits for traffic baton. One of them has 20 red LEDs and 20 green ones arranged alternatively in a flasher. The other has two bulbs in the flasher. Both circuits use 6 V, 4.5 Ah rechargeable batteries.
This battery level indicator circuit uses ten LEDs to show the level of charge in a battery. Each LED represents 10 percent of the battery level. So, the battery level can be measured to the nearest tenth level. It contains three groups of LEDs to represent the levels of battery charge; red, orange and green.
This is a circuit that acts as a wireless switch for home appliances. One needs to move his hand between the infrared led and the phototransistor to interrupt the infrared beam and the appliance starts working through the relay. When the hand is removed from the beam the appliance stops working.
This is a circuit for a car anti-theft system. Initially, when the circuit is on, an LED glows to indicate that the circuit is enabled. When someone opens the door, the circuit enables a buzzer which can be turned off by using the car key.
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