Figure shows a laser with a 60-mW output power, 1.0-cm output beam diameter, and fixed divergence of 0.2°. A photodiode will be used to measure distance from this source from 0.0 to 5.0 m using the known decrease in intensity with distance. The photodiode is used in the circuit in Figure 16a with Vs = 20 V and R = 15 kΩ For that circuit, the relation between diode reverse current and light intensity is
I(A) = 1.429 IL (W/m2)+ 57.
a. Design signal conditioning so that the distance from 0.0 to 5.0 m is converted to an 8-bit digital signal. Use an 8-bit unipolar ADC with a 10.0-V reference.
b. Plot the ADC output, expressed as a base 10 number versus distance. Comment on the linearity.