Low Cost Deaf People Doorbell

This circuit provides a delayed visual indication when a door bell switch is pressed. In addition, a DPDT switch can be moved from within the house which will light a lamp in the door bell switch. The lamp can illuminate the words "Please Wait" for anyone with walking difficulties.Circuit diagramNotes:The circuit uses standard 2 wire doorbell cable or loudspeaker wire. In parallel with the doorbell...

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Digital Counter with an Interval of Kilometers

The circuit has been designed for a person who loves to jog or walk while measuring the distance that have been covered during the activity. 4093 – a quad 2-input NAND with Schmitt trigger inputs integrated circuit, generally characterized by small fluctuation in voltage supply, very high impedance, outputs that can sink and source, one output can drive up to 50 inputs, high speed gate propagation...

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Simple Optical Theremin Circuit Diagram

Normally, Theremin works by detecting hand proximity using capacitive coupling method. A Theremin circuit shown in the schematic diagram below use different method to control the pitch. The oscillator of this tone generator, both the volume and frequency  are controlled using LDRs, a light sensitive electronic component, so we can call this circuit an optical Theremin.  Look at the...

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Low Cost Digital Code Lock

Many digital code lock circuits have been published in this magazine. In those circuits a set of switches (conforming to code) are pressed one by one within the specified time to open the lock. In some other circuits, custom-built ICs are used and positive and negative logic pulses are keyed in sequence as per the code by two switches to open the lock. Digital Code Lock Circuit diagram : A low-cost...

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