Parallax Boe-Bot Student Manual page 213

Photoresistor Divider Troubleshooting
General things to verify:
√ Check your wiring and program for errors.
√ Make sure that each component is firmly plugged into its socket.
√ Check the color codes on your resistors. The resistors that connect between Vss
and the photoresistors should be 2 kΩ (red-black-red). The resistors connecting
P6 and P3 to the photoresistors should be 220 Ω (red-red-brown).
If either the IN3 or IN6 registers showed 0 regardless of whether or not you cast a shadow
over them:
√ If the room is dimly lit, consider bringing in some extra lamps. Alternately, you can
replace the 2 kΩ resistors with 4.7 kΩ resistors (Yellow Violet Red). This will give
your resistor divider better performance under lower lighting conditions. For really
low lighting conditions, you can even use the 10 kΩ resistors (brown-black-
orange).
If either the IN3 or IN6 registers showed 1 regardless of whether or not you cast a shadow
over them:
√ If the room is very brightly lit, and you find yourself having to cup your hand over
the photoresistor's light collecting surface to make the 1 go to 0, you may need to
substitute a lower value resistor in place of the 2 kΩ. Try 1 kΩ resistor (brown-
black-red), or even a 470 Ω resistor (yellow-violet-brown) if you are outdoors.
Your Turn – Experimenting with Different Voltage Dividers
Depending on the lighting conditions in your robotics area, larger or smaller series
resistors in place of the 2 kΩ resistors may improve the performance of your shadow
detectors.
√ Remember to disconnect power to your board during each circuit modification.
√ Try replacing the 2 kΩ (red-black-red) resistors with each of the other resistor
values you have gathered: 470 Ω, 1 kΩ, 4.7 kΩ, and 10 kΩ.
√ Test each voltage divider combination with TestPhotoresistorDividers.bs2 and
determine which resistors work best under your lighting conditions. The best
combination is one that's not overly sensitive, but doesn't require you to cup
your hand over the photoresistor either.
√ Use the resistor combination that you think works best in the next two activities.
Chapter 6: Light Sensitive Navigation with Photoresistors · Page 199