I am building a temperature control module using an Arduino Nano (LGT8F328P clone), a Peltier cell for heating/cooling, a thermistance for temperature monitoring and a logic level mosfet for high current switching.
The problem I have is that when I turn on the MOSFET by setting a digital pin to HIGH (therefore letting a 5V 5A signal pass through the Peltier), my Arduino outputs higher voltages (as measured by a voltmeter) on both the 3v3 (goes to 3.7V) and 5V pins (goes to 5.9V). This higher voltage changes the reading on the analog pin, which is problematic for the thermal control loop (not mentioning the fact it could damage my board).
Here is my circuit (the 9V power supply actually represents a constant 5V 5A power supply):
Thank you for the suggestion, this is indeed how my peltier was wired during testing. I have edited my post with a proper circuit schematic if this makes it easier to read.
The "-" pole was on the termistance end that is wired to the ground.
I am trying to cool down a surface. You can ignore the resistive element before the Peltier, as the power supply is meant to be a constant 5V 5A source (no additional resistance is on breadboard).
It should be directly at the Arduino GND, or you add voltage drops on the cables. The power supply - also should go to the Arduino GND first. You found out what strange effects can result from inappropriate cabling.
Please don't go back and update diagrams/schematics, it confuses any other reader.
Can you please post some images of your project, so we can see your component layout?
You are measuring all your voltages from gnd?
Make sure ALL your gnds are secure and that the wiring for the peltier is heavy enough.
As in your edited diag below, make sure the Arduino gnd is a close to the Peltier supply gnd as possible.
Make sure that the peltier current does not flow through any other Nano circuit wires.
This diagram shows how to best connect your gnds.
Star connection at the Peltier Supply gnd.
Here is a picture of my breadboard. The thermistor is hard to see since it is out of focus, as the wire is rather long (middle/bottom of the screen).
As you can see, my arduino is grounded on the opposite end of the breadboard compared to the thermistor and Peltier power supply. I will try regrounding them as you suggested.
Thanks a lot for your suggestion. After connecting the Peltier power supply ground next to the Arduino ground, this seems to have almost entirely fixed my issue (currently running more tests).
with soldered or screwed connections. Thick GND wires.
You can build a Peltier module with the MOSFET on board. Then have the power supply connected to that board as well as the Peltier element, can both be connected by screw terminals. Have a logic GND and control signal connected to the MOSFET gate and source. This will work fine as long as the Arduino and the load (Peltier) are powered by different sources.
