This Texas Instruments circuit is from the 80's. However, it can be implemented with modern operating systems. The power supply must be symmetrical.
This circuit, shown in the figure, can operate from 4 to 100 MHz, based on a 2N2222 transistor or...
Indicated for frequency measurements, this circuit can operate with inputs up to 1 MHz. We found...
This ultra-simple circuit need a carbon microphone to operate. The circuit must be powered from D...