Difference Counter for In and Out Gates (New)
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 (New)
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.
Lithium-Ion Battery Charger (New)
Some original equipment includes charger circuit for the battery, most likely on a small part of the PCB. It is difficult to figure out which components form part of the charger circuit since no circuit diagram is normally available. In that case, we have to build our own lithium-ion charger as explained in this article.
Tester for 555 Timer and 741 Op-amp ICs (New)
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.
Desktop LED Emergency Light (New)
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.
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.
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.
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.
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.