This circuit makes use of a low impedance microphone. The relay is according to the supply voltage which can be between 9 and 15 V. The operational gain is approximately 100.
This circuit appears in several configurations in this site. This is from American documentation from...
We found this circuit in a 90s Radio Electronics. The circuit generates frequency-modulated 220 kHz signals. The...
El circuito de la figura es un regulador de corriente con ajuste en el rango de 0 a 3 ampères. El...