Super-Sensitive Photometer
Électronique / Electronic

We can use the CdS Cell to measure how bright a light is. Sometimes we might want to measure very faint light (such as from the moon or stars).

Amplifiers are useful for amplifying, things other than sound-as we'll see in this Project. You'll see why we call this a "supersensitive" photometer as soon as you finish building it. Let light fall on the CdS Cell and press the Key. You can see the Meier pointer move. Set the Control Knob to adjust the sensitivity of this circuit. You can see how this Project works by examining the schematic. What does the CdS Cell do? (No fair peeking at the answer.)

Now look at the schematic again. How do you think you could increase the sensitivity of this circuit? Got any ideas?

Okay, here's a hint ... remove the 220K resistor from the emitter-to-base circuit and see what happens. (Remember to keep notes of your results....)