i got two of theese boards which automatically turn on an IR-LED if the environment is dark (and off if its bright).
I want to be able to manually overwrite the status of the LED so I identified the ICs, took out my multimeter (on continuity test) and drawed a schematic (european symbols). Most of is seems reasonable but there are a few things I dont unterstand.
Left-hand side seems to be just a regular voltage divider between a potentiometer and a photoresistor. Right-hand side is a PNP Transistor (with current limiting resistor) to connect the LED to 3,3V. So far so good. But why is the NPN transitor in the middle connected like this? Ground at collector? Is this the so called "reverse active" mode? And when this transistor is conductive there seems to be a direct connection between 3,3V and Ground??! Why is this? I checked all the connections twice and it really is connected in such a way...
Can anybody help me unterstand this circuit?