Two HX711 Load Cell Amplifiers on Pico

1

I am trying to use two HX711 load cell amplifiers to connect two load cells to one Raspery Pi Pico.

By using the HX711 library and sample code at

I have been able to independently set up and calibrate each load cell/HX711 combination using a 686 g test weight.

The load cell amplifiers were connected (one at a time) as follows:

LC1 Dout – GPIO21 Sclk GPIO20
then
LC2 Dout – GPIO11 Sclk GPIO10

Aaron (Core Electronics) has suggested that I modify the Core sample code as follows to use both LC1 and LC2 concurrently.

from machine import Pin
from Makerverse_hx710c import Makerverse_hx710c
from time import sleep_ms

LC1 = Makerverse_hx710c(dataPin = Pin(21), clkPin = Pin(20), calibration=0.001393792)
LC2 = Makerverse_hx710c(dataPin = Pin(11), clkPin = Pin(10), calibration=0.001417685)

while True:
Data1 = LC1.read_hx710_calibrated()
print(“{:+.3f} g1”.format(Data1))

Data2 = LC2.read_hx710_calibrated()
print("{:+.3f} g2".format(Data2))

sleep_ms(90)

Using the 686g test weight I get the following results.

Actual Weight on Load Cell Reported Weight
LC1 LC2 LC1 LC2
0 0 -161 0
686 0 -161 0
0 686 +513 +686

LC2 is working correctly but LC1 is not. If I subsequently disable each HX711 in turn (remove Vcc and Grd connections) the other one again works correctly.

Help is requested to get both load cells reporting correctly.

2 Likes
2

My results table lost its formatting when posted. It should look more like the following.

Results

The problem I am having seems to be that experienced in the following post.

Any help to resolve this would be appreciated.

Fred

2 Likes
3

Hi Fred,

Awesome project!

The Makerverse Load cell uses the Picos PIO behind the scenes.
You’ll have to specify a different state machine for each:

from machine import Pin
from Makerverse_hx710c import Makerverse_hx710c
from time import sleep_ms

LC1 = Makerverse_hx710c(dataPin = Pin(21), clkPin = Pin(20), calibration=0.001393792)
LC2 = Makerverse_hx710c(dataPin = Pin(11), clkPin = Pin(10),stateMachine = 1,  calibration=0.001417685)

The code above should work.

3 Likes
4

Liam,

Yes that’s all it needed. Now working perfectly.
Thanks very much for your help.
What a great forum!

Regards,

Fred

4 Likes
5

Hi Fred,

Great to hear! No worries at all :smiley:

Keen to see what you make!

1 Like
6

Why are you using two HX711s? Are the two load cells supporting the same platform? If so then you can just connect both load cells to the same HX711.

7

John,

I am wanting to measure two independent loads so believe I have to use two HX711s.

Regards,

Fred

1 Like