Maker Factory ELECTRONICS EXPERIMENTS BOX Manual page 262

Circuits 51 and 52: The collector of T1 delivers a feedback to the base of T1 via C1. If T1 is conductive, also T2
is switched through. But the time delay causes C1 to block T1. Likewise T2 is then blocked. Via C1 transistor
T1 becomes electrically conductive again after a time delay. And so it continues.
264
Fig. 3.50: Circuit 50:
Discreet 4.4V Zener
diode
Fig. 3.51: Circuit 51: Relax-
ing pendulum clock