Load Cell Calibration
The spool holders sit on two load cells, which is how the enclosure knows how much filament you have left. They need calibrating once, with a known weight.
There are two separate procedures, and they are easy to confuse:
| What it does | When | |
|---|---|---|
| Load cell calibration | Teaches the enclosure what a gram is | Once, at build time |
| Custom spool registration | Adds a spool’s empty weight to the library | Whenever you get a new brand |
Load cell calibration
You need a known weight, meaning anything you can trust the mass of. A full water bottle, a gym plate, or something you have put on a kitchen scale. Something in the 500 g to 2 kg range works best, and using a similar weight to a real spool gives the best accuracy where it matters.
Each side is calibrated separately, so you need one weight per side. You can also do one side, move the weight across, and do the other.
Open calibration
Settings, then Configuration, then Calibration.
Empty the holders
Take everything off both sides. Nothing touching them, and no cables resting on them.
Wait for the countdown
Five seconds, and the screen prompts you when it is done. It lets the readings settle and gives you time to take your hands off, so don’t press early.
The length comes from countdownTime in data.clu if you
want longer.
Press to zero
This sets the zero point, or tare, for both cells.
Place your known weights
One on each side.
Enter the actual weights
Type in what each weight really is, in grams. Get this right, because everything downstream scales from these two numbers.
Confirm
The enclosure works out the scale factor for each side and shows you the result.
Finish
The values are saved to the mainboard’s memory. They survive power cuts and firmware updates.
Do not lean on the enclosure or bump the bench between zeroing and weighing. The whole procedure is measuring a difference, so a knock in the middle bakes the error in permanently.
Checking it worked
Put a known weight on and see if the screen agrees. If it reads roughly double or roughly half, the number you typed in was wrong, so redo it.
Starting over
The same menu has a restore factory values option, which puts both the scale and the zero
point back to the seed values from data.clu. Use it if a
calibration goes badly wrong.
The defaultLeftCal, defaultRightCal, defaultLeftOffset and defaultRightOffset values
in data.clu are only used by an enclosure that has never completed calibration, or one
that has been factory restored. Editing them will not disturb a calibrated enclosure.
Custom spool registration
This is different, and it does not touch the calibration. It measures the empty weight of a spool and adds it to your filament library, so the enclosure can subtract it and show you the filament weight alone.
This procedure assumes a full 1 kg spool. It weighs the spool, subtracts 1000 g of filament, and calls the remainder the spool’s empty weight. A part-used spool gives you a wrong answer.
If your spools are not 1 kg, change tareWeight in data.clu to match. You can also weigh
a genuinely empty spool on a kitchen scale and add it to
filament.clu by hand, which is more accurate
anyway.
Open the spool holder page
Then choose calibrate.
Empty the holder
And wait for the five second countdown.
Press to zero
Place the full, unopened spool
On either side. The enclosure takes whichever reads higher, so it does not matter which.
Confirm
The measured empty weight appears.
Name it
Up to 15 characters, and no commas.
Save
It is appended to the library and written to filament.clu on the SD card, if one is
inserted.
Doing it by hand instead
If you have an actually empty spool, weighing it on a kitchen scale and typing the number into
filament.clu beats the on-screen procedure. The load cells are good, but a spool you can
weigh directly has no 1 kg assumption in it. See
Filament Library.
Reading the display
The filament page shows net filament weight, meaning the measured weight minus the selected spool’s empty weight.
With no spool on the holder, this reads as a negative number, specifically the negative of
the selected spool’s tare weight. A 202 g spool selected on an empty holder reads -202.
That is correct rather than a fault, and it is a quick way to check that the right spool is
selected and the calibration is sane.
Troubleshooting
Readings drift. Load cells drift with temperature. Let the enclosure settle before calibrating, and don’t calibrate a cold enclosure and then expect precision at 50 °C.
One side reads sensibly, the other does not. They are calibrated independently, so redo the bad side. If it reads nothing at all, check the wiring on that cell.
Everything reads -404. That is the sentinel for “not measured”. The load cells are
switched off in the configuration, or not detected.
The calibration screen seems stuck. Wait out the five second countdown first. If it is genuinely frozen for longer, a load cell is likely disconnected, since reading a cell that never responds is what makes it appear to hang.
Weights are consistently off by a fixed amount. That is a zero point problem rather than a scale problem. Redo the calibration, making sure the holders are truly empty at the zero step.