Hi, I have circuit that is supposed to be used in car to regulate audio volume and I had bunch of noises and buzzing that I had to use galvanic isolation to eliminate that but now I have the problem how to measure car battery voltage without compromising galvanic isolation? I'm using esp32 as microcontroller and ads1115 to measure voltages. Can I add non isolated 5v buck converter just to power ads1115 and connect i2c signal to esp32 in galvanic circuit? Thanks
You could use a voltage to frequency converter then measure the frequency via an optocoupler. On the plus side they make analog optocouplers.
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Would I still use ads1115 in that case? and how accurate is it?
No it would be a digital signal. You would measure the frequency and convert that to volts. You get complete isolation with the optocoupler and the grounds are not connected unless everything is on the same ground. Check this out it appears to be close" Voltage to Frequency Converter Circuit using AD654
How accurate would voltage reading be and would I need to use voltage divider?
It can be very accurate and no need for a voltage divider, as it will be a square wave signal, it will not be analog. The analog is in the voltage to frequency section. How well you design that the better and more accurate your system.
I see it have up to 36v input power supply. Does that mean that I can connect it directly to car battery and take measurements at the same time or do i still need to convert to 5v voltage?
From what I see on the data sheet you can do just that. https://www.analog.com/media/en/technical-documentation/data-sheets/AD654.pdf I would not recmmend doing that as a finished product, it will need some protection but it will get you through the testing stages.
In your spare time look up low pass filters. That could also be a solution.
How often do you need to measure the battery voltage. Could you periodically mute the audio, with a relay measure the battery then un mute? Perhaps between songs.
Low pass filter as protector or?
It should measure constantly at at least 50-200ms refresh rate.
You could use a low pass filter for the analog input but you will lose the galvanic isolation. You could do a voltage divider, place maybe 10uf on that then from that a 10K to the A/D input. The bigger the cap the more noise it will remove and the slower the response. ---|---|---Analog input where --- = resistor | = cap. You need to keep the A/D input impedance below 10K.
Why, do you expect the battery to change significantly in 20ms?
Low pass filter rejects high frequency spikes (aka noise). It does it in such a manner that cannot be replicated with over sampling.
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