#### jopero._

Joined Oct 25, 2023
1
I'm a Computer Engineering student(from Brazil) and I'm currently immersed in a challenging project that involves electronics and programming. I need to develop a differential probe to measure voltages of 220V or even higher, with the goal of integrating this data into an STM32 microcontroller.

Most of my knowledge lies in the realm of programming, and I have limited experience in electronics and power electronics. Hardware is relatively new territory for me.

My plan is to use resistors to step down the 220V voltage to 3.3V (which is the maximum limit the STM32 can read). However, I'm a bit lost when it comes to creating an effective circuit that preserves the waveform's characteristics and makes it positive so the microcontroller can read it without loss of information.

Additionally, I'm interested in calculating the RMS value of the voltage and conducting further studies on the collected data.

If you have any experience in electronics, electrical engineering, or embedded systems programming and can share tips, resources, or guidelines to tackle this challenge, I would be extremely grateful. I'm open to any guidance and eager to learn!

#### Jerry-Hat-Trick

Joined Aug 31, 2022
494
I think maybe your circuit is more complicated than it needs to be. Certainly, a potential divider with resistors along the lines of your proposal but use a diode to chop off the negative half of the wave and just measure the positive half cycles. To get an accurate RMS value do A/D conversions at maybe 10,000 times a second, square and average them, then calculate the square root. Compensate for the diode voltage drop for greater accuracy if that’s important

I don’t see the need for op amps etc. you could full wave rectify if you think the positive and negative going voltages are not precisely the same shape

Your strings of resistors is good, important not to have voltages across resistors more than their specified maximum, with some healthy headroom.

Hopefully, you are careful about safety when using high voltages