This 1974 circuit uses two 555 integrated circuits in a very traditional configuration. The circuit can be powered by voltages from 9 to 12 V and for greater volume an amplifier stage can be added.
This 2001 CMOS digital circuit draws numbers from 00 to 99 and can be expanded. However, it does...
This filter was found in an old publication from 1977. The circuit must use a simple two-voltage source...
This circuit beeps when the sensor is triggered by the opening of the freezer door or other...