LCD weird characters - EMC

Dear All,

I created a SW to measure the voltage from some batteries of 12V 2.3Ah.

Sometimes (once on 10-15 )when I put the tips on the battery connectors, the display shows weird instead of normal ASCII characters.
I have tried to twist the cable power supply of the display but without any improvement.

Another funny thing is if I insert the Diode D2(see the png file), all pixel of the Display tuns on.

Thanks in advance for any advice

Fausto

bat tester schema.pdf (89.8 KB)

FaustoT: Sometimes (once on 10-15 )when I put the tips on the battery connectors, the display shows weird instead of normal ASCII characters.

Do you mean the system usually works?

And this undesired glitch thing occurs only sometimes?

Also - please explain what you mean by "10-15".

Hi I mean that when I start measuring the first battery all is fine and the program runs, on the display I could see what I want. After the measure the program (being a loop) return from the start. All works perfectly but after 10-15 measures for some EMI/EMC reason on the display appear strange characters.

Thanks in advance

When this LCD that you're using starts glitching ...... are you able to check your values using serial monitor? Only the LCD glitches, right? If so --- then have you tried adding a suitable de-coupling capacitor across the supply pins (eg. Vcc and GND) of your LCD module?

Hi, I have inserted the capacity but without any improvement. Now that I twist the wires and make them shorter, it seems work. I will see in the next days.

Fausto

So far as D2 goes, it looks like it is supposed to be there to protect the input from too high voltages. Now if you are measuring a 12v battery that voltage divider should be sending 2.4v to the TLV. That should be fine, the circuit looks correct on paper. I suspect that there must be a wiring issue (is the diode backwards?), because that diode should have no effect until the voltage being measured goes too high.

FaustoT:
I have inserted the capacity but without any improvement. Now that I twist the wires and make them shorter, it seems work. I will see in the next days.

It is good that there’s better behaviour now. How long are these wires? In the order of 10 cm? 1 metre? 10 metre?