Light Sensors for the Prop-2 (Sensing light levels)

[datbates]

I am doing a project which will required me to sense the amount of light shining on a light sensor and use the amount to control some servos position.  What should I use for the sensor?

[JonnyMac]

You can build a light sensor from simple components: a resistor, capacitor, and a CdS photocell.  Here's the schematic:



Be sure to use a good quality capacitor; low-quality (paper) caps are leaky and will give inconsistent results.  Here's what a subroutine to read the sensor might look like:

Get_Light_Level:
  HIGH Sensor
  PAUSE 1
  RCTIME Sensor, 1, lightLvl
  RETURN

Of course you have to define the "Sensor" pin and the "lightLvl" variable as a word.  Note, too, that the ULN2x03 will interfere with this circuit.  You could connect it to P15 and then replace the upper group ULN2803 with a ULN2003, or if you need to connect the circuit elsewhere you can simply remove (clip it) the ULN input pin that corresponds to the I/O you want to use.

Once you get everything working and know what you lower and upper limit values from the sensor are you can scale them to create a servo-compatible output pulse.