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Simple Interface for Digital Sound Synthesis    (New)

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    (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.

Simple Low-Power Audio Amplifier    (New)

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    (New)

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    (New)

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.

Wireless FM Microphone   

Presented here is a simple wireless microphone with which you can transmit the audio signal to any clear spot in 88-108MHz commercial FM band. The microphone has a range between 15m and 45m depending on the type and location of the receiver’s antenna. The unit produces high speech quality with low current drain. A conventional 9V battery powers the unit. The antenna length has been limited to keep radiation within the Federal Communications Commission (FCC) regulation for wireless microphones.

USA-style Twin Horn   

Here is a twin horn circuit, which can produce mono as well as ‘stereo’ sounds. There are three suitable sets of frequencies for a horn of this type and they are 400Hz/500Hz, 500Hz/600Hz and 600Hz/700Hz. The frequency set can be selected and tuned using available presets. The mono output produces a mix of both the frequencies from the selected frequency set. The stereo outputs have both frequencies individually on the two channels.

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.

Mains Operated Remote Control Tester   

This handy remote control tester responds to the signal received from any infrared hand-piece (IR remote control).

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.


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