Using this electronic scheme can be made a very simple function indicator that generates a tone of each two minutes. This function indicator can be used to warn that a certain electronic equipment is still under voltage, or to generate an audio warning, consisting of 5 to 10 beeps.
The circuit consists of three a square wave generators and one inverter. The first generator is represented by N1 and provides a signal with a period of about two minutes and pulse about ten seconds. During these ten seconds, the second generator enters in function state in rate of 1 Hz. At the output of N2 have ten pulses every two minutes. This output signal is inverted, so both N4 and N2 can be primed only during the 10 seconds the train of pulses coming from the N1. During these 10 seconds, N4 is activated and inhibited by ten times (which cause these beeps).