Experiment 2 - The Schmitt Trigger Circuit II

But what happens in the Schmitt trigger circuit? To understand this, it helps to go through the various steps of the circuit...

Consider the shown simplified diagram. All parts connected to the negative terminal of the battery (0 Volt) are shown in blue, all the components on a positive voltage (>0 Volt) are shown in red.

Illustration functioning Schmitt trigger I.

When the potentiometer P1 is fully turned clockwise, there is no voltage at the input (U_in = 0 V)...

• The transistor T1 is turned off and
• the transistor T2 is turned on, since via the resistors R_c1, R1 and R2 a voltage is applied to its base.

At the output is no voltage (U_out = 0 V). The LED remains dark.

What happens when you increase the input voltage U_in using the potentiometer...?