LEDs, a somewhat surprising result I wanted to see if I could make an ozone detector by looking at the ratio of absorption of yellow versus blue and red light for detection of the ozone generated spark in my air speed meter.
This can be done by switching a RGB LED, so R, G, B, sequentially and looking (with an ADC and PIC) for ratio changes with a photo detector (I wanted to use a BPW21, as I already have used that in the Tritium decay experiment, but that part needs ordering. So I was wondering what would happen if used the same RGB LED as detector and as transmitter of light, wondering if red would see red, and blue blue, and green green..
Anyways, the setup, the LED are driven by exactly 20 mA. The receiver side photo current is measured with the Chinese multimeter in the 2000 MOhm (no typo) range:
And the results, those are puzzling:
First we see red shining on red, that gives some photo current, as expected, red -> green does nothing (good) red -> blue nothing (also good).
But then.... green shining on red does something green shining on green does nothing green shining on blue does nothing mmm strange
And finally Blue shining on red gives the strongest signal yet. blue shining on green also very strong, and blue shing on blue is a lot weaker.
I color coded the receive wires, and measured everything twice, the 00 symbol means on 2000 MOhm meter range infinite. I actually measure resistance, but that is just reverse current in the LEDs.
So, from this, with the R, G, B LEDs in parallel, these LEDs should be able to detect white light..... :-) Not so sure about the spectral curve at all...