Re-purpose Qtr-1RC sensors

Hi there,

I am wondering if it would be possible to re-purpose the QTR-1RC sensor to result in a ambient light level sensor. It would be nice to have one that we could use the same way we use the QTR-1RC sensor, i.e. charge and timed discharge.

I’m thinking of replacing the phototransistor (remove the whole led/phototransistor module) with a light dependant resistor (LDR), and getting rid of the 150ohm resistor.

The normal LDR varies between very high resistance (approx 10M) when dark and much lower when in the light (from 48k to 150k) depending on the light source.

I’m not it seems to me i would probably need a smaller cap as the even in full light (48K) it’s quite high still…

What would I need to change to get this to work (if possible) or is there a better solution for getting simple analog light levels?




I have just realised that I can probably just replace the photo transistor for one that responds primarily to a wavelength more common to ambient/visible light (ie from a torch)

so that might do the trick,

Still any further input would be greatly appreciated (specs on recommended photo-transistors etc)




I think that makes the most sense. Otherwise, by the time you’re talking about potentially replacing all of the components on the QTR, I think it would be better for you to make something from scratch than try to repurpose the QTR.

- Ben