Teensy ADC giving higher than possible ADC reading

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imaditya

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Hi Guys,

I am seeing a wierd behaviour on my teensy 3.5. my circuit is in the attached picture. I am using a Phototransistor for sensing light and read this value into the ADC
teensy_adc_circuit.png

When I make the reading of the ADC and display on serial, the teensy gives value more than the possible based on the set ADC resolution. This is mostly when I shine an LED bright led directly into the phototransistor. However, I assume that even the the max brightness, the max possible value should be for eaxmple 1024 for 10 bit resultion.

Here is the output from the serial for 10 bit.

Code:
1927,19986409
1928,19986552
1928,19986695
1928,19986839
1928,19986982
1928,19987124
1928,19987267
1928,19987410
1928,19987554
1928,19987696
1928,19987840

For 13 bits

Code:
15669,18966974
15662,18967117
15655,18967260
15652,18967403
15652,18967546
15650,18967688
15651,18967832
15651,18967975


In both the outputs, the second number is the number of ellapsedMicros value for tagging each reading.

Has anyone else had this problem earlier?
 
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