Normalizing a value from HX711

[duckredbeard]

I have a scale project that is used to determine the quantity of beer in a keg. Since not all beers weigh the same, the full weight of the keg is inconsistent. I'd like to find a way to "normalize" the range of variables used for the varied weights. When I run the following code, it starts out with getting a "zero" reference then I place the full keg on. With a full keg, I get values between 500000 and 515000. How do I convert the larger number to a simple "100" so that I could use percentage of range (0-100) instead of 0-inconsistent number.

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# Scale project that uses a scale to determine the volume of beer in the keg. # A row of LEDs indicates the state of the program and the volume of the keg. # A requests post initiates a push notification to my phone when the weight of the keg changes.   import time import sys import requests from gpiozero import LED     #Define LED indicators - these are GPIO numbers LED1 = LED(21) #Blue LED2 = LED(26) #Red LED3 = LED(20) #Amber LED4 = LED(19) #Green LED5 = LED(16) #Green LED6 = LED(13) #Green LED7 = LED(6) #Green LED8 = LED(12) #Green LED9 = LED(5) #Pink   EMULATE_HX711=False   referenceUnit = 1   if not EMULATE_HX711:     import RPi.GPIO as GPIO     from hx711 import HX711 else:     from emulated_hx711 import HX711   def moving_average(prev_average, new_value, num_steps = 5.0):    return (prev_average * (num_steps - 1) + new_value) / num_steps   average = weight = 400000  #just a value close to what a newly deployed keg would be w_threshold = 2000  #approximate value of 3-4 fluid ounces of the beer   def cleanandexit():     print("Cleaning...")     if not EMULATE_HX711:         GPIO.cleanup()            print("Bye!")     sys.exit()   hx = HX711(27, 22) hx.set_reading_format("MSB", "MSB") hx.set_reference_unit(1) hx.reset() hx.tare()   print("The scale is ready")  print("put the keg on...")   LED9.blink(.2,3)  # indication that the scale is running - not blinking means program crash start = time.time()   while True:     try:                keg1 = hx.get_weight(5)         weight = keg1         keg1 = round(keg1,3)         start_weight = keg1         print(keg1, average)         if time.time() - start > 5:             weight = keg1             lost_weight = average - keg1             lost_weight = round(lost_weight,3)             if lost_weight > w_threshold:                #r = requests.post("https://bit.ly/editedforprivacy")  #Join URL that triggers push notification to my phone                print("You got served")                average = keg1  #resets average to new keg1 value for faster recovery             print(lost_weight)  #visual indication of how much was poured - one pint is about 8400             average = moving_average(average, weight)             average = round(average,3)             start = time.time()             if 8000 >= keg1 <= 507001: #keg is outside of usable range - flashes when keg is missing (indicating tare is complete at startup)             LED1.blink(.2,.2)         else:             LED1.off()           if 109800 >= keg1 >= 80000: #Red less than 5% - DANGER             LED2.blink(.5,.5)         else:             LED2.off()                       if 130600 >= keg1 >= 109799: #Amber less than 10% - Warning             LED3.on()         else:             LED3.off()                       if 507000 >= keg1 >= 130599: #  Green 10-20% - Caution             LED4.on()         else:             LED4.off()                       if 507000 >= keg1 >= 172199: #Green2 20-40%             LED5.on()         else:             LED5.off()                       if 507000 >= keg1 >= 255400: #Green3 40-60%             LED6.on()         else:             LED6.off()                       if 507000 >= keg1 >= 338600: #Green4 60-80%             LED7.on()         else:             LED7.off()                       if 507000 >= keg1 >= 421800: #Green5 80-100%             LED8.on()         else:             LED8.off()             hx.power_down()         hx.power_up()         time.sleep(1)         except (KeyboardInterrupt, SystemExit):           cleanandexit()

Keep in mind that this code's values are based on a full keg being about 507000 and an empty keg being about 89000. This works out to a net weight of about 418000, which is the weight of the beer.

I have found that I can get inconsistent "full" values using the same keg. Running this 4 times this morning, I got the following values for full: 507000, 511000, 509000, and 516000.

[deanhystad]

scale = 100 / (full - empty)
percent_full = (weight - empty) * scale

Empty is the weight of an empty keg. Hopefully this is consistent enough to be a constant. full is the weight of a full keg and would be taken just before entering the loop. It will be different for each keg.

[duckredbeard]

That seems easy enough. So what I need to do now is to tell the program when to capture the "full" value. Plobby do that with a button push, kind of like a reset function. I will see what I can do with this. Thanks for the idea.

[duckredbeard]

So I added a few things, haven't been able to test it yet. Let me know if this is what you were talking about. I only changed the part where these maths control the lights, not much else. I also added the reset button on GPIO4, expecting a push of that button will reset the "full" value to the currently observed "keg1" value that the HX711 is reporting. On paper, this looks like what I am after.

Behold the code:

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# Scale project that uses a scale to determine the volume of beer in the keg. # A row of LEDs indicates the state of the program and the volume of the keg. # A requests post initiates a push notification to my phone when the weight of the keg changes.    import time import sys import requests from gpiozero import LED       #Define LED indicators - these are GPIO numbers LED1 = LED(21) #Blue LED2 = LED(26) #Red LED3 = LED(20) #Amber LED4 = LED(19) #Green LED5 = LED(16) #Green LED6 = LED(13) #Green LED7 = LED(6) #Green LED8 = LED(12) #Green LED9 = LED(5) #Pink Reset = Button(4) #Button to reset the variable "full" to the current scale value     EMULATE_HX711=False    referenceUnit = 1    if not EMULATE_HX711:     import RPi.GPIO as GPIO     from hx711 import HX711 else:     from emulated_hx711 import HX711    def moving_average(prev_average, new_value, num_steps = 5.0):    return (prev_average * (num_steps - 1) + new_value) / num_steps   def reset_full():     full = keg1       average = weight = 400000  #just a value close to what a newly deployed keg would be w_threshold = 2000  #approximate value of 3-4 fluid ounces of the beer    def cleanandexit():     print("Cleaning...")     if not EMULATE_HX711:         GPIO.cleanup()            print("Bye!")     sys.exit()    hx = HX711(27, 22) hx.set_reading_format("MSB", "MSB") hx.set_reference_unit(1) hx.reset() hx.tare()    print("The scale is ready")  print("put the keg on...")    LED9.blink(.2,3)  # indication that the scale is running - not blinking means program crash start = time.time()    while True:     try:                keg1 = hx.get_weight(5)         weight = keg1         keg1 = round(keg1,3)         start_weight = keg1                   print(keg1, average)         if time.time() - start > 5:             weight = keg1             lost_weight = average - keg1             lost_weight = round(lost_weight,3)             if lost_weight > w_threshold:                #r = requests.post("https://bit.ly/editedforprivacy")  #Join URL that triggers push notification to my phone                print("You got served")                average = keg1  #resets average to new keg1 value for faster recovery             print(lost_weight)  #visual indication of how much was poured - one pint is about 8400             average = moving_average(average, weight)             average = round(average,3)             start = time.time()             Reset.when_pressed = reset_full               full = keg1             empty = 89000             scale = 100 / (full - empty)             percent_full = (weight - empty) * scale              if 1 >= percent_full <= 102: #keg is outside of usable range - flashes when keg is missing (indicating tare is complete at startup)             LED1.blink(.2,.2)         else:             LED1.off()            if 1.1 >= percent_full >= 5: #Red less than 5% - DANGER             LED2.blink(.5,.5)         else:             LED2.off()                        if 100 >= percent_full >= 10: #Amber less than 10% - Warning             LED3.on()         else:             LED3.off()                        if 100 >= percent_full >= 20: #  Green 10-20% - Caution             LED4.on()         else:             LED4.off()                        if 100 >= percent_full >= 40: #Green2 20-40%             LED5.on()         else:             LED5.off()                        if 100 >= percent_full >= 60: #Green3 40-60%             LED6.on()         else:             LED6.off()                        if 100 >= percent_full >= 80: #Green4 60-80%             LED7.on()         else:             LED7.off()                        if 100 >= keg1 >= 80.1: #Green5 80-100%             LED8.on()         else:             LED8.off()               hx.power_down()         hx.power_up()         time.sleep(1)           except (KeyboardInterrupt, SystemExit):            cleanandexit()

[deanhystad]

The percent_full equation converts the keg weight to a number in the range 0 to 100. This is the number you should use for calculating average and turning LED's on and off. It should be calculated each time you weigh the keg.