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...
Briefcase Alarm
This miniature alarm unit protects your valuables from theft by sounding an alarm when somebody attempts to pick up your briefcase. It is a...
DTMF Receiver IC MT8870 Tester
Today, most telephone equipment use a DTMF receiver IC. One common DTMF receiver IC is the Motorola MT8870 that is widely used in electronic...
Farmhouse Lantern-Cum-Flasher
This circuit uses a dual op-amp IC LM358 and two transistors. It can be powered by a 6V maintenance-free rechargeable battery or a lead-acid...
Logic high/low Indicator
This logic high/low indicator circuit comprises two ICs. One is hex inverter IC 7404 (IC1) and the other is a bistable multivibrator built around...
Simple Short-Wave Transmitter
This low-cost short-wave transmitter is tunable from 10 to 15 MHz with the help of ½ Jgang condenser VC1, which determines the carrier frequency...
Simple Transistor Type and Lead Identifier
A bipolar junction transistor (BJT) has three regions, of which the emitter and the collector are made of the same type of semiconductor (‘n’...
Twinkle Twinkle X’mas Star
Christmas just would not be Christmas if you do not put a flashing star on your Christmas tree. Here is the circuit of such...
