Automated Still controller - Hx711 trouble

D

Dink1000

Member
Hi

I'm trying to build a controller to semi-automate a still to distill "water".

I'm going to be using a teensy 4.0 some ds18b20 temp sensors, and a nextion display.

I've got it to a point where i can see all the temps on the display and control the outputs etc.

But i want to add a scales to weigh the collection jar and pause (turn off the heater) if it is full (90% ish).

so i bought a hx711 board and the 4 50kg load cells avaliable ( 3 different sets) but not getting any cosistancy from them.

i go through the procedure to tare it and then set a scale value using a known weight (350g glass of water) and it shows roughly 350 grams take the weight off and it goes to roughly 0grams

Then i put a 600-ish gram weight on it and it shows about 2000grams then i try a 70gram weight and it shows -40grams.

Is there something i'm doing wrong? or are these not compatible with the teensy 4.0

Is there an alternative i can use? I don't need accuracy (-+ 100grams would be more than enough). The collection jar will be about 5kg (11lbs) when full
 
I am not saying this is the case but it is almost like the load cells are being over stressed and taking a set.
 
BriComp said:
I am not saying this is the case but it is almost like the load cells are being over stressed and taking a set.
Click to expand...

yeah i did think i may have broken one of the load cells (comes as a set of 4 ) like this thats why i ordered another 3 sets (hx711 pcb and 4 50kg loads cells) but they all act the same.

I was thinking it maybe something to do with the way the teensy reads the value with it going negative with a smaller weight (one is signed and the other unsigned maybe or one being BigEndian and the other LittleEndian)
 
How is it arranged mechanically? - when loadcells are combined they need to have the correct polarity and symmetric geometry.
 
MarkT said:
How is it arranged mechanically? - when loadcells are combined they need to have the correct polarity and symmetric geometry.
Click to expand...

they were screwed in the corners to a piece of mdf (about 200mm/8in square) in some 3d printed frames to allow them to move when a load is applied. I made sure they were connected in the correct order according to a few places on the net.Like here

i tried to move the weight about on it and it did alter but only by a couple of grams so i guess it was close enough
 
Have you tried using much higher weights? The range from 0 to 350g sounds extremly small compared to the total range of 200kg.

I have no experience with these 4x 50kg setups. However, running HX711 with that single 1 or 2kg or whatever kg loadcells works fine on a Teensy 4.0 for me. I use them as input for MIDI controllers or as interface for electronic musical instruments. They work surprisingly well and sensitive.
 
TomChiron said:
Have you tried using much higher weights? The range from 0 to 350g sounds extremly small compared to the total range of 200kg.

I have no experience with these 4x 50kg setups. However, running HX711 with that single 1 or 2kg or whatever kg loadcells works fine on a Teensy 4.0 for me. I use them as input for MIDI controllers or as interface for electronic musical instruments. They work surprisingly well and sensitive.
Click to expand...

what library do you use for the interface to the hx711 ?

yeah ideally i would of prefered to use something with a 0-10kg range but all i could fine was a single bar load cell that would of been difficult to setup up and not collapse with the 5kg load on it
 
How about something like the Weigh Bridge scheme shown below.
When the flask is full it will come up to balance and close the micro switch.
Weigh Bridge.jpg
 
Dink1000 said:
what library do you use for the interface to the hx711 ?

yeah ideally i would of prefered to use something with a 0-10kg range but all i could fine was a single bar load cell that would of been difficult to setup up and not collapse with the 5kg load on it
Click to expand...

https://github.com/RobTillaart/HX711

I am successfully using such types of loadcells:
https://www.adafruit.com/product/4542
Mounting some sort of wooden plate or so with the screws is working fine.

I have no idea yet how to mount these four 50kg loadcell types reliably. I am planning to have a controller where you can step on it with your feet and have fun.
 
Happy to hear that it works now! Possibly also for others helpful to see that the library made a difference.
 
now just a case of getting the value on the nextion display.
Click to expand...
If it would be of any help I wrote an extensive library to work with the Nextion displays.
You can see it here complete with (again) rather extensive instructions.
 
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