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CORDLESS PHONE BACKUP

Normally the base of a cordless phone has an adaptor and the handset has Ni-Cd cells for its operation. The base unit becomes inoperative...

CD-ROM DRIVE AS DIGITAL AUDIO CD-PLAYER

ACD-ROM drive can be used as a stand-alone unit for playing digital audio CDs without interfacing with a computer. The stereo output of CD...

Build an Automatic Fan Speed Controller with 555

During summer nights, the temperature is initially quite high. As time passes, the temperature starts dropping. Also, after a person falls asleep, the metabolic...

COMPUTERISED MORSE CODE GENERATOR/TRANSMITTER

The circuit given here can be used to send telegraphic messages via computer. The message data entered through the computer keyboard is converted to...

Telephone Security Circuit to Prevent Unauthorised Line Use

Most of the telephone security devices available in market are simple but quite expensive. These devices provide blinking or beeping type line-tap misuse indications....

DIY Telephone Call Meter Using Calculator and Quartz Clock Circuit

In this circuit, a simple calculator, in conjunction with a COB (chip-onboard) from an analogue quartz clock, is used to make a telephone call...

Connect Two Telephones in Parallel Without Interference

Often a need arises for connection of two telephone instruments in parallel to one line. But it creates quite a few problems in their...

Ultrasonic Proximity Detector

We the humans can hear sound of up to 20kHz frequency only. This proximity detector works at a frequency of 40 kHz. It uses...

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...

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...

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...

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...

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...

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...

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 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...

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