Science Buddies: "Ask an Expert"

Hi, I am currently conducting the project 'build a light-tracking bristlebot'.
For the base circuit, can I connect the photoresistor in series with the potentiometer and the gate of the MOSFET?

Pc_Tan - Simple answer, no. The FET is controlled by a voltage level that is established by the photoresistor and potentiometer. The FET is has such a high input resistance, that it would likely 'see' the full battery voltage instead of the voltage established at the node of the photoresistor and potentiometer if simply connected in series as you suggest. If the FET was, in fact, a bipolar transistor that reacted to BASE current, your idea might be valid. What was your thought about changing the circuitry? Curious.

Rick Marz

Rick - Thanks for your advice. I was thinking If I can adjust the sensitivity of photoresistors in another way stated in the project but it seems that it won't work.