Voltage Divider on ADC Differential Pi
1091 Views - Created 21/06/2021
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?
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. https://www.abelectronics.co.uk/tools/resistor-voltage-divider
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 https://www.ti.com/lit/an/sloa054e/sloa054e.pdf
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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