AC to DC conversion and measurement using arduino uno board

I have already designed a circuit for the above mentioned topic but the issue with it is while reading the ADC value from Arduino board I am unable to get get back the Voltage value given as input. For example if my input was 70V and the same equivalent value will be stepped down via Step down transformer following it has a bridge diode and Voltage divider designed to have an Output which is fed to ADC pin of Arduino.So now for the said input my output will be converted to equivalent output and it gives some ADC value which is then taken for calculation in my Arduino code.But the issue here is I am unable to get back the same 70V as AC voltage.I may get around 56-60v.Why is this happening?Is there any changes to be made in my hardware circuit ?Please help me solve this issue.I have looked for many sites showing hardware connections for the said
topic but all circuits behave same.


by Jeevan_jinnu
August 21, 2018

by mikerogerswsm
August 22, 2018

Your diodes will drop about 0.6V each. This subtracts 1.2V from the voltage entering the 10k/16.2k potential divider and therefore subtracts about 0.8V from the indication.

I would suggest using a higher voltage out of XFMR2 with an appropriately higher value of R1. There will still be a diode drop to allow for, but it will be less as a proportion.

Remember to scale for rms as appropriate.

by mikerogerswsm
August 22, 2018

Your circuit as shown measures average. The form factor here is 1.11

by mikerogerswsm
August 22, 2018

Form Factor:

by mikerogerswsm
August 22, 2018

I don't know if this helps, but if you want to perform full-wave rectification without the diode-drops, a precision full-wave rectifier does the trick swimmingly.

by mk5734
August 22, 2018

Another method is to use the AD736

This is accurate for all waveforms and does not need to have any form factor applied.

It all depends what you are measuring and what accuracy you require.

by mikerogerswsm
August 22, 2018

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