When more weight, the value goes down

[adriencarbonaro]

When I put more weight on the scale, the value goes down in the negatives. Maybe the offset is not well calibrated, but the value should go up when I put more weight. Does someone know why ?

[gandalf15]

Simple solution. Just turn the load cell by 180 degree in vertical axis. Sometimes the manufacturer puts the sticker other way around. This should help.

[adriencarbonaro]

I'll do that if there is no software solution but the load cell is already fixed so it is not so easy to turn it around. Do you know a software solution ? Otherwise I'll do just that. Thank you !

[gandalf15]

Sure, we can solve it in software. I'll look at it tomorrow.

[gandalf15]

Meanwhile, can you provide more info? Which function you want to use? is it get_weight_mean? Do you "zero" (tare) the scale with hx.zero method? I think that if you set the variable hx._scale_ratio_A_128 = - ratio to negative ratio this should just work fine. Then do not use hx.set_scale_ratio(scale_ratio=ratio) method to set the ratio. There is check if the ratio is negative it raises ValueError. You have to access the variable as described above. As I said I'll look at it tomorrow. Let me know if this worked.

[adriencarbonaro]

I'll provide more info this afternoon! I'll try your solution and tell you if it works

[adriencarbonaro]

I think it is a problem of ratio and offset. I'm not sure to understand how to set them.

[gandalf15]

If you are using channel A and gain 128 try this and copy the output. If not working try debug mode. Also, do not forget to change your dout_pin and pd_sck_pin to your pin numbers.

hx = HX711(dout_pin=21, pd_sck_pin=20)
result = hx.reset()
result = hx.zero(readings=20)
input('Put known weight on the scale and then press Enter')
data = hx.get_data_mean(readings=20)
if data != False:
    known_weight_grams = input(
        'Write how many grams it was and press Enter: ')
    value = float(known_weight_grams)
    print(str(value) + ' grams')
    ratio = data / value  # calculate the ratio for channel A and gain 128
    print('data:', data)
    print('known weight is:', value)
    print('Ratio should be for you a negative number. It is:', ratio)
    hx._scale_ratio_A_128 = ratio  # in this case ratio should be negative number
else:
    raise ValueError('Cannot calculate mean value. Try debug mode.')
while (True):
    current_weight =  hx.get_weight_mean(10)
    print('Current weight on the scale is:', current_weight)

[gandalf15]

You can try to pull the latest changes from master branch. the example.py should work.

[adriencarbonaro]

Sorry I didn't have much time to respond before. Thank for the info. I did what you told me too and it worked like a charm. I then pulled your latest changes that did the exact same thing so it is great now. I'll be using your library a lot in the next few weeks so I'll come back if needed.

Thank you again, great work.