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# Voltage Divider on ADC Differential Pi

The ADC Differential Pi is an Analogue to Digital converter for the Raspberry Pi

1091 Views - Created 21/06/2021

21/06/2021

Posted by:
jevers99

Hi,

When using the ADC Differential Pi, do you have any suggestions for reading voltages outside of -2.048 - 2.048? Is it possible to add a voltage divider for examplke?

Thanks,

Jon

22/06/2021

Posted by:
andrew

Location:
United Kingdom

Hi Jon

There are two methods you can use to reduce the voltage level to work on the ADC Differential Pi.

You can use a voltage divider with the positive side going through the R1 resistor before connecting to the ADC + input and the negative connecting directly to the ADC - input. The R2 resistor connects ADC + and ADC -. We have a calculator you can use to get the values for R1 and R2 based on your input voltage. Resistor Voltage Divider Calculator

The second method is to use a fully-differential amplifier. An op-amp circuit is more complicated than a resistor divider but it does have the advantage of a higher impedance between the + and - inputs. Texas Instruments has a good article explaining how to use fully-differential amplifiers at sloa054e

09/08/2021

Posted by:
BriggTrim

Hi.... that appears reasonably agent yes. So the issue is with respect to the differential nature of the voltage perusing I'm attempting to take - the tall end of this perusing must be underneath 5v add up to (and here is 11.1v aprox.). I'm understanding that now. So, would the arrangement here be the swapping the arrange of the resistors (and the ADC examined tests) so that the 11.1v to begin with has got to pass through the bigger resistor? 7pcb

09/08/2021

Posted by:
andrew

Location:
United Kingdom

Hi

With an 11.1v input, you would need resistor values of 10K for R1 and 2.2K for R2 which would give you an output voltage of 2.002V.

With this voltage divider setup, you can have a positive or a negative input voltage. A -11.1V input would give you an output voltage of -2.002V.

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