Circuit monitors blinking phone lights


Posted on Jul 30, 2012

A 2N5777 photo-Darlington cell picks up blinking light from the transparent plastic buttons. The power is switched ON and OFF by a hi-beta 2N3904 transistor. The circuit's 9 V battery can be left continuously connected. Less than a micro-ampere is drawn-even with normal, office ambient light and the phone lights not flashing.


Circuit monitors blinking phone lights
Click here to download the full size of the above Circuit.

For noisy locations, the tone can be made louder with an output transformer (ratio of 250:8) or a 100 ohm speaker that replaces the 22 ohm resistor in the output.




Leave Comment

characters left:

New Circuits

.

 


Popular Circuits

Antennas for HAM transmitters
1 KHz Audio Oscillator schematic
Robot eyes
Medium-power-inverter
Switching Circuit
CD4040 Generating Long Time Delays Circuit
All Transmitter & Receiver schematics
Amplifier Schematic
Night security light
6V Ultra-Bright LED Chasers
planning build mosfet h bridge motor control
12V-220V Modified Sine-wave Inverter Circuit
Transmit Audio Cable
555 the DC capacitor tester



Top