Has anyone had noisy extruder temp readings with a Rambo board?
We have a lulzbot that has very erratic and noisy readings for the extruder, temp jumps of 3 degrees or more.
We replaced the whole extruder+hotend assembly with a spare, and it still happens. PID autotune won’t work because it can’t acquire a steady oscillation.
I checked the 5v voltage at the regulator and at the thermistor, it’s steady.
I checked the voltage drop across the thermistor, and it’s predictable without any discernable jumps in voltage levels. It looks smooth in rate while heating or cooling.
I checked the resistance of the wires and didn’t see any issues.
I’m really stumped, and getting ready to just buy a new board.
I have erratic readings on one of my RAMPS boards if it’s only powered by USB and the main power is off. Obviously only ambient temps are possible to read since there’s no power to the heaters.
I’m assuming it’s some sort of grounding issue or perhaps (in my case) just a noisy 5v line that somehow smooths out once the main 12v is turned on.
Obvious stuff: make sure the temp sensor wiring is not running immediately parallel to any heater or stepper wiring, and twist the heater wires / motor coil pairs to reduce noise radiation.
Could be a bad ADC input or broken ground somewhere. A board swap would be an easy diagnostic test if you have an alternate.
Yeah, it’s a lulzbot so I’m hoping that they at least twisted the wires. The sleeving they use is a tight fit, and all the wires are in it, so of course it’s all parallel to everything else. I’d expect to see the noise on the multimeter, but it looked quite steady.
The noise happens over a few seconds, id expect to see that, but I haven’t done the calculations to determine just how much noise translates to voltage.
The Rambo is a funny board, they put all sorts of diodes on the thermistor inputs to prevent esd damage, however the vref for the adc isn’t used as the voltage source for the thermistors (and the vref has a LC filter on it). Completely pointless if you ask me.