This circuit for very long-time intervals was found in the March 1993 Radio Electronics magazine. Times of several days or even weeks can be achieved depending on the value of C1.
This 2005 circuit from a Linear Technology manual makes use of the LTC610HV and an optical coupler that...
This digital mixer uses CMOS integrated circuits. The circuit was published by us in a magazine...
This circuit was found in Motorola documentation from the 80's. The MOSFET admits equivalent...