This filter for frequencies from 300 Hz to 3.4 kHz was found in the February 1995 Radio Electronics magazine. Other operational amplifiers can be experimented, and the source must be dual.
This traditional two-tone alarm configuration with the 4011 integrated circuit was found in a 1998...
This circuit indicates the resistance of the skin of those who hold the electrodes. RV1 makes the...
The transistor of this circuit can be a BD135 or TIP31. The load current is given by resistor R1....