Letterbox with Letter-Counting Facility (New)
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 (New)
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 (New)
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 (New)
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.
Speed Controller for Small Cooling Fans (New)
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 fanís speed when temperature rises, and vice versa.
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.
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.
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.