Printer Model: Custom
MCU / Printerboard: Arduino Uno
Host / SBC: Raspberry Pi
klippy.log
Fill out above information andin all cases attach yourklippy.logfile (use zip to compress it, if too big). Pasting yourprinter.cfgis not needed Be sure to check our “Knowledge Base” Category first. Most relevant items, e.g. error messages, are covered there
Describe your issue:
I have connected the wires for a thermistor to my Arduino Uno at Analog Pins 3 and 4. Whenever I connect the power supply, the temperature reading jumps up about 20 degrees, and when I disconnect, it jumps back down. It occurs both when the thermistors are connected and when they are disconnected. My temp circuit has no joined connection to the heater. The power supply for the stepper motors is 24V 2.5A. I need help to figure out the cause of this bizarre behaviour. Thank you logs-20250723-204803.zip (132.6 KB)
I would like to see the wiring for the entire printer including how you are powering the printer. Of particular importance, especially in this case, is understanding how GND/VIN- is wired.
Why are you using a 100k resistor as the pull up for your thermistor? Traditionally it’s 4.7k 1%.
This is the diagram for the connections to the 24 V. I have tried to disconnect the probe, but the temp still fluctuates. Both the thermistor temps show the same fluctuation. Only other thing powered by the 24V are the stepper motors. Nothing else is connected to the circuit. I googled how to connect a thermistor to Arduino, and it said to connect a 100k thermistor to a 100k resistor. Sry for the bad drawing. Thank you
Sry for the confusion. The probe is the Inductive Proximity Sensor LJ12A3-4-Z/BX.
I have a Raspberry Pi Model B with the original Raspberry Pi 15W adapter. I am powering the Uno with the USB A to B wire. Excluding the stepper motors, I have three endstops, two MOSFETs (Powered by an Arduino 5V), and a Proximity sensor. Those 2 MOSFETs are for the hotend heater and the part cooling fan. I will change the resistor, but for now, I wanted to find the problem here. Should I disconnect the probe GND from the 24V and try again?
The shield is placed on top of the Arduino Uno. I will attach its schematics in the next post.
I have attached the pic of my setup. It’s messy—Sry for that.
I have another 12V power supply that is only used for the fan and the hotend heating. It is only connected through the MOSFET and isolated from the Uno. When I disconnect and reconnect, the temps don’t change.
I have attached the updated drawing, which includes the 12V option. Really sry for the bad drawing. Thank you
Please confirm that the Arduino Shield is attached to the Arduino Uno and the Arduino Uno is powered by the Raspberry Pi that it is attached to - correct? That is what I’m taking from what you’ve written.
What is the 24V power supply that you’re using? Is it plugged into the wall and how is it wired? I want to understand how you’ve connected AC “Earth” (if you’ve done so).
What is the 12V power supply? Is it plugged into the wall and how is it wired? I want to understand how you’ve connected AC “Earth” (if you’ve done so).
Now, for the “HotEnd” and “Fan” MOSFETs, you don’t have a common ground between the MOSFET’s Source and GND on the Arduino Shield - you’re driving the Gate without a reference to the Gate’s voltage.
Oh. I got it. I cut the probe wire from the GND of the thermistor and connected it to the GND on arduino and it worked. Now it doesn’t fluctuate anymore. Thank you for helping me out
My impression is, 100k Ohm (pull-up resistor) is way too weak.
I would stick to the Klipper documentation Configuration reference - Klipper documentation and try it.
I wonder about heater_bed: target=0 temp=-80.5
from your klippy.log. Why is “temp=-80.5” negative and so off from the target temperature?
and extruder: target=200 temp=107.1
follows with the same pull-up. Why?
