The existence of field effect transistors at the input of the integrated circuit (operational amplifier) of this application makes it possible to use them in timers for long periods. In fact, the time constant obtained with 144 M ohm resistors (7 22 M ohm resistors in series) together with the 10 uF polycarbonate capacitor, leads to a timing of 1,000 seconds. The integrated circuit must have symmetrical power supply and the clear switch is used to discharge the capacitor at the beginning of a new timing.
