QTR-A at 3.3v

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1

I want to change the QTR-A (single line sensor) to give a 0 to 3.3v ranged reading from an initial 5v source.

How would I do this?

I can figure out the LED side of things on my own, but doesn’t the 47k resistor divide the output between itself and the photoresistor? I’m still new to all of this and still learning, but I need to convert one of these sensors to feed a 3.3v uController and I’m struggling to understand how it works.

If i added another voltage divider to the output, my current instincts says it would cause the sensor to not function properly. (like say a 18k/33k divider circuit). Correct?

-Epic

2

Hello.

Do you have access to the 3.3V you are using to power your microcontroller? If so, the sensor could just work for you when powered at 3.3 V. The IR LED will be a bit dimmer, but that might not matter much for your particular application. Alternatively, you could put a 100k pull-down resistor on the sensor output so that the output voltage never exceeds ~3.4V (but it will still drop to zero as the phototransistor’s resistance goes to zero).

- Ben