DIY Photometer Schematic

 

Shown above is the updated schematic of the DIY Photometer from Yang et.al.

The prototype deviates from this schematic in the following areas:

  1. the blue LED is connected to a 1K resistor in series with the the 1K potentiometer.
  2. the blue LED  GPIO pin is digital 8
  3. The green LED GPIO pin is digital 9
  4. The light detector output is on GPIO pin analog 3

wirewrap

Comments. The 1k resistor reduces the  blue LED intensity and prevents saturation of the detector.  The one I put in is huge – but I have these on hand. A 1/4 watt resistor would fit in better.   I moved the  LED GPIO pins to test pulse width modulation (pwm) as a light intensity dimming mechanism. I tested  on pin 9 which is pwm enabled – this didn’t work  well, hence the 1k resistor.  pwm could be tested further …seems like it should have worked.

 

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