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Author Topic: ADC values not zero when plugged into ground and turning on LEDs  (Read 1041 times)
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I was thinking about this and I don't remember reading anything that stated that different types of capacitors had different charge/discharge rates.  Could you give me some place where I could find such information?

Straight from the horse's mouth: http://www.atmel.com/Images/DOC0484.PDF
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Well, I only have two power buses and one is dedicated to the IR LED circuit and the other is dedicated to the detection circuit.  And the only difference between them is that each uses a different ground.
Are the two grounds electrically the same?
Not sure about the two power buses, are they from a different source?
Either way, as I said, that simply can't happen if it is wired as described. Think about it, all that you are doing is adding a capacitor across the supply, this can't affect the signal. What were you seeing that made you think there was a delay.

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different types of capacitors had different charge/discharge rates.
Well I would not say they are different  charge/discharge rates but the capacitive reactance and effective series resistance are different with different types of capacitors.
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Are the two grounds electrically the same?
No, different GND pins.

Not sure about the two power buses, are they from a different source?
No, same source.  What I mean by power bus is that I've got a breadboard with two buses going down each side.  I'm connecting the LEDs to one and the sensor to the other.  Each connected to a separate ground pin.

Either way, as I said, that simply can't happen if it is wired as described. Think about it, all that you are doing is adding a capacitor across the supply, this can't affect the signal. What were you seeing that made you think there was a delay.

Ok, here's my data.  Numbers on right of graph are values I've received from ADC, the graph is a representation of those numbers.  ON represents when the LEDs are switched on, OFF when they are off:

With no caps:


With 235uF on LED circuit:


With cap on sensor circuit:


It sure does look like the signal is being delayed.  That or its being inverted.  Oh, BTW, the values were taken when the sensor was partially blocked from the IR LEDs.

Straight from the horse's mouth: http://www.atmel.com/Images/DOC0484.PDF
Thanks for this. I'll have to read it later.
« Last Edit: April 04, 2013, 04:57:00 pm by adrian_h » Logged

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Looks like I don't need more caps.  Just 3 or 4 of these 47uF were enough.  I actually was getting signals from the ceiling when I had all 6 IR LEDs on. smiley-grin  I may only need 1 or 2 IR LEDs on for this project.
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