This circuit uses uncommon Texas Instruments components today. The circuit is from an American documentation. Transistors are commonly used PNP. The display is 7 segment multiplexed.
With the configuration shown in the figure, we have the relay being activated when the microphone picks...
This TTL generator that can function as a control shield or external clock for microcontrollers was found in...
The OP07 operational amplifier is not common today, as the circuit is from an old European manual....