This little circuit is a 3 tone generator. Back in the late 1970's and 1980's EDCOR used this generator on the a number of input modules that were used in their modular power and mixer amplifier. This module would supply a tri-tone to the amplifier when a set of connection was complete. It was use security and notification across the background sound system. A simple usage, would be to have the tone sound out of the background music system when a door was open. There was a lot of different applications it was used in. It is a simple circuit, but then simple is good when designing. It could be used on any line level input. It was used to signal an alarm or buzzer when pin 2 and pin 3 of T1 were connected together.
The generator needs a bipolar power supply of 15 volts DC. When a switch connects pin 2 and 3 of T1 a tone is generated out pin 1 of P1.
You can change the sound by changing R3, R4 and R5.
Note on connector P1:
- Pin 1 is tone out
- Pin 2 is +15 VDC
- Pin 3 is ground
- Pin 4 is -15 VDC
- Pin 5 not used
- Pin 6 not used
