Optical sensor

[pcremades]

Hi Alex,
Just a simple question. Why did you make the hole facing the photodiode and the one facing the LED so small? How did you choose the diameter?

regards,

[vektorious]

Hey Pablo,
the hole is determining the aperture. The sensor is very sensitive and by changing the hole diameter one can regulate the light load on the sensor. The size for the hole is empirical and I usually have to widen it a bit with a hot needle to get the best measuring range. That's something you have to test:

1. Assemble the photometer, determine the max measure value by shining light directly on the sensor.
2. Set the sensitivity of the sensor (poti at the back) so the value of a measurement with a water-filled test tube is a bit (50 units) below the maximum value.
3. If you never reach max value with a water-filled test-tube (and setting the poti at the back of the sensor pcb) you have to increase the hole size.