Simple Adjustable Staircase Waveform Generator Staircase signals find many applications in the field of electronics, such as in television systems, telemetry, and analogue and digital communications. Here is a circuit illustrating the basic principles of staircase waveform generator.
Mini Offline UPS Here is a circuit of an offline UPS, which a hobbyist can make at a reasonable cost. The capacity of the UPS is 350VA, so it can be used for any equipment with a load below 350VA. The UPS can be upgraded to 1kVA by making just a few changes.
Letterbox with Letter-Counting Facility Here is a circuit that starts counting when you insert a letter in the letterbox at your home or office. It is designed to save your time from going to the letterbox to check if there are letters inside. The number of letters present in the box is indicated by a seven-segment display.
Low-Cost 6-Bit DAC For controlling the load of appliances such as cooling fans, low-wattage heaters, thermostats, low-wattage light sources, small electrical toys and test benches for loudspeakers, we need a power source whose voltage can be controlled in small steps and is capable of providing current of more than 1A. For that, we require low-resolution digital-to-analogue converters (DACs) with three to seven bits.Here is the circuit capable of setting output voltage between 1.25V and 15V in 64 steps.
GSM-based Dot-matrix Display Presented here is a GSM-based, eight-digit dot matrix display that can show an eight-digit message sent via any mobile phone, from any place around the world, to the mobile number of the SIM in the GSM module of the display. Size of the display is 7×40, which is made using 5×7 dot-matrix LED modules.
Sensitive LPG Leakage Alarm Here is an ultra-sensitive LPG sensor that generates loud beeps when it senses any gas leakage. It detects vapours of liquefied petroleum gas anywhere between 200 and 10,000 ppm and drives a piezobuzzer to catch attention for immediate action. The buzzer beeps until the concentration of gas in the air decreases to a safe level.
Mini Rechargeable Power Supply Presented here is a robust, compact and hand-held power supply that delivers 9.2V and 5V up to 1A (approx.) and 3.3V up to 500mA. It also includes a female A-type USB connector so you can power and charge other equipment such as mobile phones. Four white LEDs are included to enable its use as a torch-light as well.
Simple 12V, 1A SMPS This is the circuit of a simple 12V, 1A SMPS. It is is built around a low-power offline switcher TNY266 (IC1), photo-transistor photo-coupler EL817 (IC2), a flyback transformer (X1) and some other easily-available components.
Electronic Door Lock Home burglary incidents are on the rise. Homes without proper security measures in place are particularly more vulnerable. But, it is easy to avoid home break-ins by using a simple solution like the electronic door lock presented here. With this circuit installed, the entry door of your house can be unlocked only by entering a pre-decided password, which helps to prevent unauthorised unlocking.
Rainbow Clock Here is a simple circuit using different colour LEDs that makes your clock glow in different colours of rainbow.
Buffer and Driver for Square-Wave Signals Here we describe a buffer and driver circuit for square-wave signals. The circuit has a high output driving capability and high slew rate of the output signals. It can provide TTL- and CMOS-compatible signals.
Speed Controller for Small Cooling Fans Small cooling fans are used in some equipment for cooling semiconductor devices. The circuit given here is of a simple automatic speed controller for a 12V, 0.6W (or 1.2W) cooling fan that increases the fan's speed when temperature rises, and vice versa.
Battery-Discharge Measurement Circuit Battery-life measurement for a portable system is a time-consuming task and many methods used for it do not give reliable results. Presented here is a circuit using which you can measure the battery-life very easily. Here, an analogue clock tracks the discharge time of the battery used in battery-powered portable devices.
Door-Knock or Vibration Alarm This is a simple circuit that activates an alarm when there is a knock on the door or there are any vibrations due to movement of heavy goods or furniture. The circuit uses readily available components.
Automatic Evening Lamp Presented here is a solution for switching off outdoor lamps even when you are not at home. The lamp turns on in the evening and turns off in the morning so that there is no need for manually switching it on/off.
Difference Counter for In and Out Gates Sometimes, we need to know whether someone is still inside a building before it is locked. And if so, how many persons are still inside? There can be many other similar situations for which the circuit presented here can come handy.
Efficient 5V Relay Driver This design idea outlines a method to use an analogue switch and discrete components to reduce the power dissipated in relay actuation. We introduced a power-saving relay-driver circuit for a 12V relay in May issue. Presented here is an MAX4624-based circuit to drive a 5V relay in a more efficient way.
Versatile Audio-Visual Alarm This circuit uses an NE555 timer IC, some LEDs, a couple of piezo buzzers and a few other components to produce audio-visual effects as per your requirement. The timer NE555 and its equivalents are widely used for all sorts of audio and visual indications, such as door alarms.
Brushless DC Motor Driver Use of brushless DC motors (BLDCs) is on the rise. But their control usually requires rotor-position information for selecting the appropriate commutation angle. Normally, a Hall Effect sensor is used to sense rotor position. But in cost-sensitive applications, a sensor-less commutation scheme is often desirable. The circuit described here uses a DRV10866 driver IC to drive a small BLDC fan, without using any position sensors.
Alcohol Level Tester A lot of accidents happen every day due to drunk driving. This is a very useful circuit for testing whether a driver is drunk or not. The circuit is easy to use, inexpensive and indicates various levels of alcohol consumption through LEDs.
Tester for 555 Timer and 741 Op-amp ICs Sometimes you do not get proper output from a circuit due to faulty ICs. This circuit can test timer 555 and op-amp 741 ICs, which are commonly used in projects, to save you from this problem.
Rotation Counter Presented here is a simple rotation counter which helps you measure the revolutions per minute (rpm) of any rotating object. As the project requires measurement of very high rpm, a fast-switching device like a reed switch is used. A small round magnet is mounted on the blade as shown in Fig. 1 to activate the reed switch on each rotation. The circuit has been successfully tested up to 6000 rpm but it can measure even beyond that.
Simple Interface for Digital Sound Synthesis You can make a digital sound synthesizer, for experimentation with sound equipment or with peripheral devices, using special integrated circuits or digital-to-analogue converters (DACs). But here is a simple 8-input digital sound-synthesis circuit for producing audio from digital codes that can be easily interfaced with microcontroller or microprocessor boards having up to eight TTL/CMOS-level digital output pins.
Desktop LED Emergency Light You can make an ultra-simple desktop emergency light using discharged batteries. You know that battery cells still have considerable energy left in them even when these become weak for most battery-powered devices. Here is a way to extract their leftover power for use in such applications as emergency light.
Simple Low-Power Audio Amplifier The small-signal amplifier is generally referred to as a voltage amplifier because it usually converts a small input voltage into a much larger output voltage. The audio power amplifier works on the basic principle of converting low-power audio signal to a suitable level to be delivered to the load. This low-power amplifier circuit is useful for the amplification of sound from small-signal devices such as mobile phones, laptops or desktops.
Monitor for 6V/12V Batteries Rechargeable batteries of 6V and 12V are used in a large number of applications. It is imperative that these are maintained properly to get maximum life out of them. Further, their permissible number of charge-discharge cycles must be fully utilised. Here is a circuit that gives a visual as well as an audible alarm if the battery voltage is higher or lower than acceptable limits, so that corrective action can be taken.
Power-Saving Relay Driver In many circuits, the switching action is performed by a relay, which in turn activates an external load. The power consumed by the relay may be unsuitable for battery-powered applications. Here is a simple solution using some inexpensive components to considerably save power.
Simple Tester for 74xx04 and 74xx14 ICs The integrated circuits (ICs) 74xx04 and 74xx14 are very frequently used and reused during circuit design. Here xx stands for HC, HCT, AC and LS, etc. Sometimes, the internal inverters of these ICs get damaged. So, it is very important to test these ICs before initiating any experiment and sometimes during the experiments.Presented here is a simple circuit which can test these ICs statically and dynamically.
Distance Counter Presented here is a simple pedometer circuit. It measures the distance covered by you while walking. It may not work very well for running!
Multi-tone Configurable Alarm Presented here is a multi-tone configurable alarm that can be activated by temperature and other physical parameters. Its output tone can be selected through different switch combinations. Such an alarm is highly desirable when multiple alarms are present in the same area. Different tones can be selected for different alarms so that you can easily know which alarm has triggered. The alarm in this circuit is activated by temperature.
Precision 1Hz Clock This precision 1Hz clock uses just two ICs and one junction field-effect transistor (JFET) in conjunction with a commonly available crystal and a handful of other passive components.
Subwoofer for Cars This system needs to be attached to an existing car stereo amplifier to add extra 'boom effect' to the music. It has a dedicated loudspeaker with a power amplifier to boost low frequencies that are normally omnidirectional.
Intelligent Water Pump Controller with Water-level Display Most of the circuits for multi-level indication/control of water in tanks employ a bunch of wires running between the circuit and the overhead tank, which accounts for almost half the cost of the entire project. Here is an intelligent scanned water-level indicator-cum-pump controller circuit that utilises just four wires to the overhead tank to indicate nine different levels.
Infrared Proximity Detector This proximity detector using an infrared detector (Fig. 1) can be used in various equipment like automatic door openers and burglar alarms. The circuit primarily consists of an infrared transmitter and an infrared receiver.
Water-Level Indicator Here is a simple water-level indicator for overhead tanks that uses three LEDs (LED1, LED2, and LED3) to indicate minimum, middle, and maximum water levels in the tank.
PWM-Based Speed Control for DC Motors There are several methods for controlling the speed of DC motors. One simple method is to add series resistance using a rheostat. As considerable power is consumed in the rheostat, this method is not economical. Another method is to use a series switch that can be closed/opened rapidly. This type of control is termed as chopper control. We’ve described here a PWM-based chopper circuit that smoothly controls the speed of general-purpose DC motors.
LED Sand-Glass Timer This circuit simulates the old sand-glass timer. A total of 32 LEDs create the effect of sand grains passing from the upper half of sand-glass to its lower half.
Garage Light and Security Control Useful for vehicle owners, this gadget automatically turns on indoor/outdoor garage lights and raises an alert when an automobile enters the garage.
Locker-Security Alarm Presented here is a simple locker security alarm that can be used to protect a locker from unauthorised access. The circuit is low-cost and forms a fool-proof alarm that receives its control signal from a standard reed switch. The circuit works off a 12V DC power supply.
RJ45 Cable Tester Described here is a simple RJ45 cable tester circuit which can be used for testing the RJ45 network cables. The circuit can check both straight-through and crossover-type RJ45 network cables. This is a low-cost tester designed using easily available components. Fig. 1 shows the difference between straight-through and crossover network cables.
Medicine-Time Reminder We are all so busy with our daily lives that we forget to take our medicines on time, which can have several ill effects on our health. The circuit described here helps in making a simple reminder that allows you to set an alert for the medicines that you need to take. The device flashes an LED or rings a buzzer at the selected time intervals.
Automatic Room-lock and Lights circuit This circuit counts and indicates up to nine persons present in the room and automatically locks the door and switches off lights as soon as they leave. It automatically switches on the lights when the first person enters the room. The circuit can be used as a power-saving device and a security device to prevent unauthorised entry in the room, especially in a business meeting room.
Humidity Indicator and Controller Presented here is a simple humidity indicator and controller. In industries such as textile, the change in moisture content has a direct impact on the properties of fabric, such as tensile strength, elasticity, fibre diameter and friction. Therefore the process is executed within a permissible humidity environment only.
Human-Machine Interface through Electromyography Electromyography (EMG) is a technique of recording muscular activities by measuring the potential difference across a muscle of interest. EMG signal acquisition is the latest trend as it paves way for a new method of human-machine interface (HMI). Here, the signals sent by brain are received as a potential difference across the muscle.
Temperature-Sensing Diodes Selector Low-cost semiconductor diodes such as 1N914, 1N4148 and 1N400X can be used as temperature sensors in applications where high accuracy is not required. They can be mounted on transistors, power diodes, transformers, heat sinks, rechargeable batteries, crystals, PCB, etc to monitor their temperature.
Electric Shock Gun This is a fantastic circuit for self-protection. In case a burglar intrudes your house, you can use this security circuit as a weapon for self-protection by giving a mild electric shock to the attacker.
Automatic Water Pump Motor Controller Municipal corporations in many cities supply water during early morning hours. So, you have to wake up early, just to switch on your motor pump and wait till your water tank is filled up. Further, there is no control for overflow of the tank. Many times you come to know of your overflowing tank only when your neighbour informs you.
Anti-Theft Alarm for Vehicles This simple and inexpensive anti-theft circuit for vehicles sounds an alarm simulating a police siren whenever someone attempts theft of your vehicle. The alarm sounds continuously for a few seconds even when the intruder switches off the ignition key. The circuit uses only a few components and can be easily assembled and installed on a car with negative grounding.
Sound Scanner This novel sound scanner sweeps all sound vibrations in its vicinity and converts them into audible beeps. It can sense sound vibrations up to a distance of 6 metres and can be used to monitor sitouts, car porchs, and other places of your house. The sound scanner operates a beeper whenever the microphone detects a sound.
Precision Null Detector Precise determination of null point in AC/DC bridges helps us to evaluate accurate values of circuit components like L and C. Here is a null detector that has many merits.
Low-Range AM Radio Transmitter Here is a simple radio transmitter for transmission up to 25 metres. It is basically an AM modulator whose signal can be received on the normal AM radio. It can also be used as an AM radio tester.
0-100°C Temperature Detector Here is a temperature monitoring system capable of remote temperature reading without transmission losses in the conditioning circuit. The IC AD590 (IC4) is used as a temperature transducer. This semiconductor transducer provides a current output proportional to absolute temperature.
Simple FM Receiver Frequency modulation is used in radio broadcast in the 88-108MHz VHF band. This bandwidth range is marked as FM on the band scales of radio receivers, and the devices that are able to receive such signals are called FM receivers. The FM radio transmitter has a 200kHz wide channel. The maximum audio frequency transmitted in FM is 15 kHz as compared to 4.5 kHz in AM.
Intruder Detector Using Laser Torch Here is a simple, low-cost intruder detector that uses an invisible laser beam to detect the intruder. The laser beam is produced using a 3V DC or 4.5V DC laser pointer or torch that is available in the market. The 3V DC or 4.5V DC power supply for the laser transmitter can also be given using a bridger ectifier or full-wave rectifier.
Solidstate Signal Lamp This solidstate signal lamp is a good alternative to revolving mechanical signaling lamps used in ambulances. It uses ultra-bright blue LEDs for signaling. However, you can replace blue LEDs with bright red LEDs for other applications.
PC-Driven LED Display Here is a circuit to generate sequentially running light effects using a simple program written in C. The output of the program is taken from the LPT port of a PC and then fed to the interfacing circuit for the LED display. The outputs of the interfacing circuit are decoded, inverted, and then connected to LEDs through optocouplers.
Parallel Telephone With Secrecy And Call Prevention This circuit provides secrecy when two or more telephones are connected in parallel to a telephone line. The circuit also prevents incoming calls to as well as outgoing calls from other telephones connected in parallel, except from the one lifted first.
False Triggering Eliminator For Timer 555 Normally, false triggering of timer IC 555 takes place during power on, resulting in unwanted output, which starts the timers time cycle. The circuit becomes inefficient especially when the load has to be energised only when desired. Here is a simple circuit to eliminate false triggering of timer 555.