This simple transistorized timer can be used to remind an activity such as telephone use, heater on, pump on etc. It beeps at an interval of one minute to remind the activity. The circuit is too simple and can be assembled in 10 minutes.
Two complementary transistors T1 and T2 are wired as an oscillator with the timing components R1,R2 and C1. The frequency of oscillation depends on the charging and discharging of the capacitor C1.