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...
Picnic Lamp
You can take this white LED based night lamp on your picnic outings. The lamp has sound trigger and push-to-on facilities and gives ample...
Infrared Interruption Counter
Most optical interruption counters make use of a light bulb with light-dependent resistor (LDR) or ordinary phototransistor as the sensor. The interruption counter work...
Little Door Guard
If some intruder tries to open the door of your house, this circuit sounds an alarm to alert you against the attempted intrusion.
The circuit...
Power Failure And Resumption Alarm
This circuit gives audio-visual indication of the failure and resumption of mains power. The circuit is built around dual timer IC LM556. When mains...