Showing results for 
Search instead for 
Did you mean: 

Electromagnetic interferences with an STM32F769I-DISCO board

Associate II


For some weeks, I have been using an STM32F769I-DISCO board as the centrepiece of a new industrial solution which enables us to know how much paper has been consumed by a studied machine. Therefore, firstly, an inductive sensor is used and generates a signal which corresponds to a certain quantity of consumed paper. This signal is injected to two analog inputs of the microcontroller: "A0" & "GND". Of course, there is always before a voltage reduction of this signal (indeed, the voltage of the sensor's signal is around 24V and, after using a voltage divider, the voltage of this signal turns out to be equal to approximately 2.63V, so lower than 3.3V).

However, I encountered a problem when I used this board inside a production area where some electric engines were activated. Indeed, through a test where the solution with the board had been deployed just over a production machine with an electric engine, some electromagnetic interferences seemed to be liable for an automatic incrementation of the counter developed in the microcontroller. For that matter, the voltage readers developed just before in the microcontroller showed there were some voltage peaks whereas the voltage was supposed to be equal to 0V at those moments. Those peaks were higher than the threshold value which is initially used to allow the incrementation of the counter.

Therefore, I really need your help about the devices I may use in order to protect the board from the electromagnetic disturbances. What kind of filter might I use? The useful signals of the sensor will never have a frequency higher than 40Hz.

I truly thank you in advance for your help!




Thank you very much for your complete answer!

Unfortunately no, I have to try to carry out all the steps of this project all by myself.

Therefore, I tried to follow your instructions, and I created a simulation model with LTspice.

Here's below the schema I drew, does it match with what you thought about it some hours ago?


Here, V1 corresponds to the voltage output of the voltage divider.

V2 corresponds to the power supply outputs of the STM32 board ("3.3V" and "GND") I'm going to use to supply the opamp.

At the output of the opamp, there's the simple RC filter which has a cutoff frequency of 1.6 kHz.

I truly thank you in advance for your help!



Yes, that looks very good.

Maybe you have to adapt the capacitor size to your signal.

For the opamp, look for some "single supply RRIO" (rail-to-rail input / output) which can work with 3.3V ***, and spend another 100 nF cap close to the opamps VCC / GND pin to connect between 3.3V and GND.

So now connect that circuit between the input divider / filter and the STM32 IO.

*** opamps: ss we're at ST here, you might use:



I hope you can solder that... 😉

Hello! Thank you so much for all your help!

Yes, I think I will be able to solder the components.



Well, remember that this might not yet be the solution to your EMI problems, maybe only one of many steps.

Remember the case and check how to ground it.

Associate II

Yes, about that, we have just bought a metal case which will be grounded.

I am going to carry out some tests after mounting this electronic circuit and putting it inside the case.

Hopefully, the EMI problems will be resolved.