QTI Sensor not giving any voltage output (Solved)

SRLM

I tried hooking up a QTI sensor from parallax (www.parallax.com/Portals/0/Downloads/docs/prod/robo/28108-QTILineFollower-v2.0.pdf), but it doesn't give me any voltage output. My setup:

B - ground
R - output
W - 5v (measured 4.9v)

I am using my multimeter to see what the voltages are, and all I get on the red wire is 0 (+- a few mv). I have tried it on 7 QTI sensors, all with the same results. Any suggestions?

edited title.

Post Edited (SRLM) : 11/17/2009 3:32:11 AM GMT

Franklin

What are you holding in front of them and how close?

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- Stephen

SRLM

I have tried white paper at all distances and my hand at all distances. There is no significant change, although there does seem to be a few mv of corresponding change.

Phil Pilgrim (PhiPi)

The QTI sensor output is open collector. Did you remember the pullup?

-Phil

SRLM

Okay, I didn't realize a pullup could be useful. I tried various values, from 10k to 500 ohms. The 10K seems to be the best, but it is still very rough. Only about 2 volts are used, and it is from 1v to 3v or so. Is there a way that I can make it go the full range (0 to 5)? I'm interested for two reasons. First, to see if I can use the sensors as a digital sensor and secondly to extend the accuracy of using an ADC with the sensors.

PJAllen

Try a higher value resistor (pull-up).· The voltage out·should be at its greatest when the incident irradiance is least (nil), so make sure that it's "dark", and it·may or may not·get to "0" without some extraordinary full-on exposure.

SRLM

Thanks PJ. I tried 20K and 100K. The 20K gave me a range of .2v to 4v, while the 100K gave a range of .1v to 1v. I assume that the remaining 1.2v on the 20k resistor is just due to environmental factors.