ADC measuring circuit for microcontroller

Thread Starter

Gaurav Gupta_1568212829

Joined Sep 11, 2019
I have to measure 110V DC using a microcontroller(5V). But at the same time I need to keep the microcontroller safe from high voltage.
One method that I know is to use a voltage divider and limiting the voltage using a zener diode. The calculated value of the resistors are R1=210K and R2 = 10K.

Now instead of using a single 210K resistor I can use series of resistor so that if any resistor gets short the voltage will still be in control because of the zener diode.Now what I want to know is that are there any other better ways which can keep the controller safe.

Thank you.
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Joined Oct 29, 2013
The best protection is get a stand alone ADC that will handle the 110V and has a communication interface such as SPI or I2C, then isolate it from the processor by sending the communication lines through an opto isolator.

If you choose to wire it direct to the micro controller via a voltage divider, put a big series resistor on the processor input pin, and a zener (or TVS) diode to ground next to it. The resistor will keep current under control, and the zener will dump anything over your chosen voltage direct to ground, hopefully sparing your processor. But pay attention to the voltage curves of the zener, make sure it's fully conducting before the absolute maximum voltage rating for the processor input pin.

Edit --> Also note that a zener will have some leakage which may affect your voltage reading depending on how much it leaks, so take that into account.
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Joined Mar 14, 2008
You could also use a Schottky diode after the resistor divider to the micro power rail (cathode to rail).