#9162
LectronFan
Moderator

Hi Michael !

The Lectron set makes experimenting fun and always challenging.
I like to take classic circuits (like the Schmitt trigger) and create something completely new around this !

Has anyone figured yet out how the oscillations occur ?

Well here’s some explanation :

First, the capacitor starts to charge via R2 and P1.
As soon as the level of the Schmitt trigger is reached, the output of T2 goes HIGH (negative voltage – PNP transistors !) and thus driving T3 to make the lamp go on.
As T2 blocks, the voltage across R7 drops.
This causes the E of T1 going more positive (PNP transistors !). The gain of T1 rises and this is speeding up the process of the Schmitt trigger.

But now, the capacitor will discharge through the B-E junction of T1 and R7 quite rapidly.

This causes the Schmitt trigger to return to start position.

Many greetings,

Frank