Make: Volume 95

PROJECTS: Amateur Scientist

DO-IT-YOURSELF PHOTODIODE

AMPLIFIERS

The circuit in the sensor board shown in Figure

B includes an op-amp that significantly improves

the circuit’s sensitivity. The op-amp converts

the change in resistance of the photoresistor

into a voltage. Op-amp circuits that amplify the

photocurrent generated by a photoresistor or

photodiode are called transimpedance amplifiers

(TIAs).

Figure

C

shows a basic TIA that amplifies

the photocurrent from a photodiode. Resistor

R

f

controls the circuit’s amplification factor or

gain, which in this basic circuit is the resistance

of R

f

. Therefore, when R1 is 10,000 ohms, the

circuit amplifies ...