Delay then off for tone signal

Question

I have a simple circuit using a 555 timer as an oscillator to output a 12v tone to an intercom system. I'd like to make a delay circuit that will turn off the output of my circuit after a delay.

1. Tone output of first circuit turns on timer while passing through to intercom system for approx. 30 seconds
2. Delay circuit turns off tone for a set time approx. 2-5 minutes.
3. Tone passes through to intercom again for 30 seconds and then off again.

Is this possible? Using an oscillator output to run another timer circuit? Will the charging circuit cause the volume of the tone signal to drop as the timing capacitor charges?

Answer 1

The output of a 555-based astable multivibrator is a square wave, transitioning at two points on the capacitor charge / discharge curve. The output does not track the capacitor charge curve, it has a flat high and flat low. So no, the tone volume should not drop with capacitor charging.

This is true in an ideal circuit, but there may be two caveats for the actual implementation:

• If the tone circuit is entirely powered by the multivibrator's output, it is worth checking if the output of the 555 can cope with the current demand, both average and transient, of your tone generator.
• Depending on the impedance of your power rails and the design of your circuit, both the tone circuit's volume, and the timing for both the oscillators, could either droop or glitch.

Please share a schematic for more specific responses.

Answer 2

Programmable logic timers are ~0.40 ea in single qty. You can use them to make events from milliseconds to months with variable clock RC and selectable counts of 256,1k,8k or 64k

CD4551B

Here I used the clock out as the tone gnerator and 30 second timer which resets the programmable delay timer, which then resets the 30 second timer into an endless cycle. It has internal POR or power on reset.

Some details I left to your imagination.