Is there any difference between ADS1115 inputs?

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rbardsley
 
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Is there any difference between ADS1115 inputs?

Post by rbardsley »

I have a single LED that shines on two different light sensors of the same model. I have one hooked up to ADC0 and the other to ADC2. They are right next to each other on the board. The LED is positioned in the middle of them. I have a reference voltage that is applied to ADC 1 and ADC 3 to give me a more accurate differential reading as the output from my light sensors varies between 2VDC and 4VDC. ADC 1 and ADC3 are tied together.

However, I am consistently seeing two different differential reading from my light sensors. I am running a temperature calibration routine that cycles the board from 50F to 110F and back. One light sensor is very even and only varies about 17mV over that range. (I am doing a lot of temperature compensation of the LED brightness to maintain that) The second light sensor on ADC2 varies about 375mV over the same range with the same LED. It's variation is directly proportional to the temperature.

Why would there be any difference? Same sensors, same light source, same board.

Is there something special going on inside the chip that I am not aware of?

Thanks,

Ryan

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adafruit_support_mike
 
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Re: Is there any difference between ADS1115 inputs?

Post by adafruit_support_mike »

All semiconductors are temperature sensitive (a diode makes a fairly good thermometer) but you should see the same variation on both sensors.

As a quick test, try swapping the connections between the sensors and the ADCs. That will give us more information about the actual source of the error.

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