Secret Bell
Many people move through the corridors and steps in multistoried buildings. As most of them are strangers for the inhabitants of the flats, it...
Capacitance-Multiplier Power Supply
High-quality audio amplifiers require a very efficient power supply with negligible ripple, hum and buzz. An ordinary bridge-type power supply has a drawback in...
Variable Power Supply Using a Fixed-Voltage Regulator IC
A voltage regulator (also called a ‘regulator’) with only three terminals appears to be a simple device, but it is in fact a very...
Telephone Operated Calling System
Dual-tone multiple-frequency (DTMF) receiver IC is commonly used in telephone equipment. One common DTMF receiver is Holtek HT9170 used in electronic communication circuits. The...
Friendly Charger for Mobile Phones
Most mobile chargers do not have current/voltage regulation or short-circuit protection. These chargers provide raw 6-12V DC for charging the battery pack. Most of...
Medium-Power FM Transmitter
The range of this FM transmitter is around 100 metres at 9V DC supply.
The circuit comprises three stages. The first stage is a microphone...
Micro-Power Flasher
With this micro-power flasher you can baffle the intruders trying to break into your home. The unit continuously emits flashing light both during day...
A Fourth-Order Speech Filter (Based on Texas Instruments Application Note)
Human speech generally occupies an audio spectrum of 300 to 3400 Hz. There is a requirement, especially in telephone circuits, to limit the frequency...
Hearing Aid
This low-cost, general-purpose electronic hearing aid works off 3V DC (2x1.5V battery).
In this circuit, transistor T1 and associated components form the audio signal preamplifier...
Remote-Controlled Fan Regulator
Using this circuit, you can change the speed of the fan from your couch or bed. Infrared receiver module TSOP1738 is used to receive...
