Procedure



Create testing circuit. (see Fig. 1)



We used the LM741 OP-Amp provided (pinout in Fig. 2) in our kits to raise the output of the BPW20RF photodiode to more measurable levels.



Through the formulas provided in Fig. 3, we were able to calculate a gain value for the OP Amp.



We settled on using a 15k Ohm resistor R1 and a 1.5k Ohm resistor as R2, and we got the value of gain as 11 (which is approximately a factor of 10).



Create testing jig (see Fig. 4)



We used a resealable box to be our test jig for this experiment. The reasons for this choice were as follows:



Resealable

Low-cost

Adaptable



Once we created our circuits, we placed them in the box with our test LEDs on one end and the photodiode on the other (see Fig. 4).



Test the LEDs



We used the two LEDs included in our kit for this test (Amber and Orange). Although we cannot tell the difference between the light these LEDs produced with our eyes, the photodiode gave us different voltage values for each LED.



Analysis



We decided to test the angle of the LEDs, as opposed to distance which could not be easily measured by our jig.



Angle

LED 1

LED 2

Zero value (no light)

3.78V

3.62V

90° (theoretical maximum value)

5.35V

5.23V

45° (theoretical minimum value)

3.83V

3.67V

60°

4.32V

4.25V



Through the above values, we can see that there is a correlation between the angle of incidence of the light, and the output voltage.



Conclusion



We can see that the angle of incidence is directly proportional to the value of the voltage emitted by the photodiode.