Did you use Led_on pin of QTR-8A to cancel ambient light like in the link below?
Thanks.
elm-chan.org/works/ltc/report.html
Each LED is wired to one MCU pin in ChaN’s design. He scans the sensors in sequence to cancel the ambient light by sampling the output voltage, turning on the LED, sampling again the output voltage, turning off the LED and getting the diffence between the two samples for each sensor.
The LEDON pin of the QTR-8A can be used for turn on/off all the LEDs in configuration four strings of two. It is just for power saving. Have a look at the schematics.
pololu.com/catalog/product/960
Actually it would be nice if Pololu would produce a sensor board that supports control each LED individually (preferably driven by a shift register to save pins on MCU).
Our LED on/off control is not just for power saving. You can turn off all the LEDs, read the sensor values, and then turn them on and read the sensor values. Having the LEDs paired up in series also halves the current you need to use for the LEDs.
Have you done any tests on individual LED on/off control compared to turning them all on and off at the same time?
- Jan
You are totally right in case the ambient light comes only from any source of light that is not a sensor of the array.
Unfortunately I can’t do any tests because I use only your QTR-8A. I am sure that you have done some tests on design stage of your sensor arrays. Any advice?
Sorry, I’m confused. I thought you said earlier that you did have individual LED control in your setup. I have never done a comparison, and a single control line for all LEDs has worked fine as far as I could tell.
- Jan
I think it is not important to onn-off all leds seperately. Because ambient lights come from sun or other IR sources.
Did you connected li-po batteries in series? Am I right they are 7.4V li-po batteries?