Analog inputs PGA gain

I use the D21G board and I have an analog input signal that is in the range of 0-0.5V. I want to measure with the best accuracy this signal so I have set the ADC resolution to 18 bits.

According to the code the ADC is the MCP3422/3/4 and which has 4 programmable gains that can be configured by setting properly the last two bits of the I2C reguest byte. So, in order to increase the accurasy and reduce the quantization noise I tried to increase the gain. But every gain setting except the x1 seems that returns only one constant value regardless the input voltage. Even the 0-5V setting of the Indio library seems to return the same constant value.

Do I miss something?

Manolis
Manolis
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Asked on 11/25/17, 1:32 PM
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Hi Manolis, i can confirm that there is a problem with the V5 setting (and other PGA settings in the library): the input voltage is compared to a reference voltage of around 5V (zero point for the raw values), and when we switch on the PGA, this reference point remains the same, meaning that e.g. with a PGA of 4, we can only measure in the range 5V +/- 1.25V  (1.25V being 5V / 4).

Tom
Tom
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Answered on 11/28/17, 5:12 AM
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Asked: 11/25/17, 1:32 PM
Seen: 143 times
Last updated: 11/28/17, 5:16 AM