Once you've finished setting up your QT Py ESP32-S2 with CircuitPython, you can access the code and necessary libraries by downloading the Project Bundle.
To do this, click on the Download Project Bundle button in the window below. It will download as a zipped folder.
# SPDX-FileCopyrightText: 2022 Liz Clark for Adafruit Industries # SPDX-License-Identifier: MIT import time import board from digitalio import DigitalInOut, Direction, Pull from adafruit_ht16k33.segments import Seg14x4 from cedargrove_nau7802 import NAU7802 from calibration import calibration # I2C setup with STEMMA port i2c = board.STEMMA_I2C() # alphanumeric segment displpay setup # using two displays together display = Seg14x4(i2c, address=(0x70, 0x71)) # start-up text display.print("*HELLO* ") # button LEDs blue = DigitalInOut(board.A1) blue.direction = Direction.OUTPUT green = DigitalInOut(board.A3) green.direction = Direction.OUTPUT # buttons setup blue_btn = DigitalInOut(board.A0) blue_btn.direction = Direction.INPUT blue_btn.pull = Pull.UP green_btn = DigitalInOut(board.A2) green_btn.direction = Direction.INPUT green_btn.pull = Pull.UP # nau7802 setup nau7802 = NAU7802(board.STEMMA_I2C(), address=0x2A, active_channels=2) nau7802.gain = 128 enabled = nau7802.enable(True) # zeroing function def zero_channel(): """Initiate internal calibration for current channel; return raw zero offset value. Use when scale is started, a new channel is green_btned, or to adjust for measurement drift. Remove weight and tare from load cell before executing.""" blue.value = True print( "channel %1d calibrate.INTERNAL: %5s" % (nau7802.channel, nau7802.calibrate("INTERNAL")) ) blue.value = False print( "channel %1d calibrate.OFFSET: %5s" % (nau7802.channel, nau7802.calibrate("OFFSET")) ) blue.value = True zero_offset = read_raw_value(100) # Read 100 samples to establish zero offset print("...channel %1d zeroed" % nau7802.channel) blue.value = False return zero_offset # read raw value function def read_raw_value(samples=100): """Read and average consecutive raw sample values. Return average raw value.""" sample_sum = 0 sample_count = samples while sample_count > 0: if nau7802.available: sample_sum = sample_sum + nau7802.read() sample_count -= 1 return int(sample_sum / samples) # function for finding the average of an array def find_average(num): count = 0 for n in num: count = count + n average = count / len(num) return average # calibration function def calculateCalibration(array): for _ in range(10): blue.value = True green.value = False nau7802.channel = 1 #value = read_raw_value() print("channel %1.0f raw value: %7.0f" % (nau7802.channel, abs(read_raw_value()))) array.append(abs(read_raw_value())) blue.value = False green.value = True time.sleep(1) green.value = False avg = find_average(array) return avg # blink LED function def blink(led, amount, count): for _ in range(count): led.value = True time.sleep(amount) led.value = False time.sleep(amount) # zeroing on startup display.fill(0) display.marquee("CLEAR SCALE CLEAR", 0.3, False) time.sleep(2) display.fill(0) display.print("ZEROING") time.sleep(3) # zeroing each channel nau7802.channel = 1 zero_channel() # Calibrate and zero channel display.fill(0) display.print("STARTING") # variables and states clock = time.monotonic() # time.monotonic() device reset_clock = time.monotonic() long_clock = time.monotonic() mode = "run" mode_names = ["SHOW OZ?", " GRAMS?", " ZERO?", "CALIBRTE", " OFFSET?"] stage = 0 zero_stage = 0 weight_avg = 0 zero_avg = 0 show_oz = True show_grams = False zero_out = False calibrate_mode = False blue_btn_pressed = False green_btn_pressed = False run_mode = True avg_read = [] values = [] val_offset = 0 avg_values = [] for w in range(5): nau7802.channel = 1 value = read_raw_value() # takes value reading and divides with by the offset value # to get the weight in grams grams = value / calibration['offset_val'] avg_read.append(grams) if len(avg_read) > 4: the_avg = find_average(avg_read) oz = the_avg / 28.35 display.print(" %0.1f oz" % oz) avg_read.clear() time.sleep(1) while True: # button debouncing if blue_btn.value and blue_btn_pressed: blue_btn_pressed = False if green_btn.value and green_btn_pressed: green_btn_pressed = False green.value = False # default run mode # checks NAU7802 every 2 seconds if run_mode is True and (time.monotonic() - clock) > 2: nau7802.channel = 1 value = read_raw_value() print(value) value = abs(value) - val_offset print(value) #value = abs(value) values.append(value) # takes value reading and divides with by the offset value # to get the weight in grams grams = value / calibration['offset_val'] oz = grams / 28.35 if show_oz is True: # append reading avg_read.append(oz) label = "oz" if show_grams is True: avg_read.append(grams) label = "g" print(avg_read) if len(avg_read) > 10: the_avg = find_average(avg_read) display.print(" %0.1f %s" % (the_avg, label)) avg_read.clear() val_offset += 10 clock = time.monotonic() if (time.monotonic() - reset_clock) > 43200: run_mode = False show_oz = False show_grams = False zero_out = True reset_clock = time.monotonic() # if you press the change mode button if (not green_btn.value and not green_btn_pressed) and run_mode: green.value = True # disables run mode (stops weighing) run_mode = False show_oz = False show_grams = False # mode is set to 0 mode = 0 # display shows the mode option display.print(mode_names[mode]) blue.value = True green_btn_pressed = True # advances through the modes menu if (not green_btn.value and not green_btn_pressed) and mode != "run": green.value = True # counts up to 4 and loops back to 0 mode = (mode+1) % 5 # updates display display.print(mode_names[mode]) green_btn_pressed = True # if you select show_oz if (not blue_btn.value and not blue_btn_pressed) and mode == 0: # show_oz is set as the state show_oz = True label = "oz" blue.value = False # goes back to weighing mode mode = "run" blue_btn_pressed = True display.print(" %0.1f %s" % (the_avg, label)) run_mode = True # if you select show_grams if (not blue_btn.value and not blue_btn_pressed) and mode == 1: # show_grams is set as the state show_grams = True label = "g" blue.value = False # goes back to weighing mode mode = "run" blue_btn_pressed = True display.print(" %0.1f %s" % (the_avg, label)) run_mode = True # if you select zero_out if (not blue_btn.value and not blue_btn_pressed) and mode == 2: # zero_out is set as the state # can zero out the scale without full recalibration zero_out = True blue.value = False mode = "run" blue_btn_pressed = True # if you select calibrate_mode if (not blue_btn.value and not blue_btn_pressed) and mode == 3: # calibrate_mode is set as the state # starts up the calibration process calibrate_mode = True blue.value = False mode = "run" blue_btn_pressed = True # if you select the offset if (not blue_btn.value and not blue_btn_pressed) and mode == 4: # displays the curren offset value stored in the code blue.value = False display.fill(0) display.print("%0.4f" % calibration['offset_val']) time.sleep(5) mode = "run" # goes back to weighing mode show_oz = True label = "oz" display.print(" %0.1f %s" % (the_avg, label)) run_mode = True blue_btn_pressed = True # if the zero_out state is true if zero_out and zero_stage == 0: blue_btn_pressed = True # clear the scale for zeroing display.fill(0) display.print("REMOVE ") zero_stage = 1 blue.value = True green.value = True if (not blue_btn.value and not blue_btn_pressed) and zero_stage == 1: green.value = False # updates display display.fill(0) display.print("ZEROING") blue.value = False # runs zero_channel() function on both channels nau7802.channel = 1 zero_channel() display.fill(0) display.print("ZEROED ") zero_out = False zero_stage = 0 # goes into weighing mode val_offset = 0 run_mode = True show_oz = True label = "oz" display.print(" %0.1f %s" % (the_avg, label)) # the calibration process # each step is counted in stage # blue button is pressed to advance to the next stage if calibrate_mode is True and stage == 0: blue_btn_pressed = True # clear the scale for zeroing display.fill(0) display.print("REMOVE ") stage = 1 blue.value = True # stage 2 if (not blue_btn.value and not blue_btn_pressed) and stage == 1: blue_btn_pressed = True # runs the zero out function display.fill(0) display.print("ZEROING") blue.value = False nau7802.channel = 1 zero_channel() display.fill(0) display.print("ZEROED ") stage = 2 blue.value = True # stage 3 if (not blue_btn.value and not blue_btn_pressed) and stage == 2: blue_btn_pressed = True blue.value = False display.print("STARTING") blink(blue, 0.5, 3) zero_readings = [] display.print("AVG ZERO") # runs the calculateCallibration function # takes 10 raw readings, stores them into an array and gets an average zero_avg = calculateCalibration(zero_readings) stage = 3 display.fill(0) display.print("DONE") blue.value = True # stage 4 if (not blue_btn.value and not blue_btn_pressed) and stage == 3: # place the known weight item # item's weight matches calibration['weight'] in grams blue_btn_pressed = True blue.value = False display.fill(0) display.print("PUT ITEM") stage = 4 blue.value = True # stage 5 if (not blue_btn.value and not blue_btn_pressed) and stage == 4: blue_btn_pressed = True blue.value = False display.fill(0) display.print("WEIGHING") weight_readings = [] # weighs the item 10 times, stores the readings in an array & averages them weight_avg = calculateCalibration(weight_readings) # calculates the new offset value calibration['offset_val'] = (weight_avg-zero_avg) / calibration['weight'] display.marquee("%0.2f - CALIBRATED " % calibration['offset_val'], 0.3, False) stage = 5 display.fill(0) display.print("DONE") blue.value = True # final stage if (not blue_btn.value and not blue_btn_pressed) and stage == 5: blue_btn_pressed = True zero_readings.clear() weight_readings.clear() calibrate_mode = False blue.value = False # goes back into weighing mode show_oz = True label = "oz" display.print(" %0.1f %s" % (the_avg, label)) val_offset = 0 run_mode = True # resets stage stage = 0
Upload the Code and Libraries to the QT Py ESP32-S2
After downloading the Project Bundle, plug your QT Py ESP32-S2 into the computer's USB port with a known good USB data+power cable. You should see a new flash drive appear in the computer's File Explorer or Finder (depending on your operating system) called CIRCUITPY. Unzip the folder and copy the following items to the QT Py ESP32-S2's CIRCUITPY drive.
- lib folder
- calibration.py
- code.py
Your QT Py ESP32-S2 CIRCUITPY drive should look like this after copying the lib folder, calibration.py file and the code.py file.
Install the cedargrove_nau7802 CircuitPython Library
Follow along with the steps outlined in this guide to download the cedargrove_nau7802 CircuitPython library and upload it to your QT Py ESP32-S2 CIRCUITPY drive lib folder. The library is a part of the CircuitPython Community Bundle.
The calibration.py file holds two important values for the main code.py file: offset_val
and weight
. weight
is the known weight in grams that you use to calibrate the NAU7802. The offset_val
is the calibration number used to divide against the raw value from the NAU7802 to find the actual weight on top of the scale.
Each strain gauge is slightly different, so you'll want to edit the calibration.py file with your known weight item and the offset_val
you generate after running the calibration mode in the code.py file.
First, the LED segment displays, buttons, button LEDs and NAU7802 are setup.
I2C setup with STEMMA port i2c = board.STEMMA_I2C() # alphanumeric segment displpay setup # using two displays together display = Seg14x4(i2c, address=(0x70, 0x71)) # start-up text display.print("*HELLO* ") # button LEDs blue = DigitalInOut(board.A1) blue.direction = Direction.OUTPUT green = DigitalInOut(board.A3) green.direction = Direction.OUTPUT # buttons setup blue_btn = DigitalInOut(board.A0) blue_btn.direction = Direction.INPUT blue_btn.pull = Pull.UP green_btn = DigitalInOut(board.A2) green_btn.direction = Direction.INPUT green_btn.pull = Pull.UP # nau7802 setup nau7802 = NAU7802(board.STEMMA_I2C(), address=0x2A, active_channels=2) nau7802.gain = 128 enabled = nau7802.enable(True)
Functions
There are a few functions for the NAU7802. zero_channel()
is from the cedargrove_nau7802 library and resets the NAU7802 to be zeroed out. The blue button's LED blinks as the zeroing process takes place.
# zeroing function def zero_channel(): """Initiate internal calibration for current channel; return raw zero offset value. Use when scale is started, a new channel is green_btned, or to adjust for measurement drift. Remove weight and tare from load cell before executing.""" blue.value = True print( "channel %1d calibrate.INTERNAL: %5s" % (nau7802.channel, nau7802.calibrate("INTERNAL")) ) blue.value = False print( "channel %1d calibrate.OFFSET: %5s" % (nau7802.channel, nau7802.calibrate("OFFSET")) ) blue.value = True zero_offset = read_raw_value(100) # Read 100 samples to establish zero offset print("...channel %1d zeroed" % nau7802.channel) blue.value = False return zero_offset
read_raw_value()
reads the raw value from the NAU7802 and is also from the cedargrove_nau7802 library.
# read raw value function def read_raw_value(samples=100): """Read and average consecutive raw sample values. Return average raw value.""" sample_sum = 0 sample_count = samples while sample_count > 0: if nau7802.available: sample_sum = sample_sum + nau7802.read() sample_count -= 1 return int(sample_sum / samples)
find_average(num)
is a quick function for finding the average of an array of values.
# function for finding the average of an array def find_average(num): count = 0 for n in num: count = count + n average = count / len(num) return average
calculateCalibration(array)
is the function used for calibrating the NAU7802 to find the offset_val
. It runs read_raw_value()
ten times and appends those values to an array. That array is averaged and the average is returned.
def calculateCalibration(array): for _ in range(10): blue.value = True green.value = False nau7802.channel = 1 #value = read_raw_value() print("channel %1.0f raw value: %7.0f" % (nau7802.channel, abs(read_raw_value()))) array.append(abs(read_raw_value())) blue.value = False green.value = True time.sleep(1) green.value = False avg = find_average(array) return avg
blink(led, amount, count)
is a quick function for blinking an LED. You pass the LED's pin for led
, length of time for each blink for amount
and number of blinks for count
.
# blink LED function def blink(led, amount, count): for _ in range(count): led.value = True time.sleep(amount) led.value = False time.sleep(amount)
Startup Reading
On startup, the NAU7802 is zeroed and then an initial reading is taken and displayed in ounces. The displays and button LEDs let you know what is happening in the code.
# zeroing on startup display.fill(0) display.marquee("CLEAR SCALE CLEAR", 0.3, False) time.sleep(2) display.fill(0) display.print("ZEROING") time.sleep(3) # zeroing each channel nau7802.channel = 1 zero_channel() # Calibrate and zero channel display.fill(0) display.print("STARTING") for w in range(5): nau7802.channel = 1 value = read_raw_value() # takes value reading and divides with by the offset value # to get the weight in grams grams = value / calibration['offset_val'] avg_read.append(grams) if len(avg_read) > 4: the_avg = find_average(avg_read) oz = the_avg / 28.35 display.print(" %0.1f oz" % oz) avg_read.clear() averaging = 0 time.sleep(1)
The Loop
The loop has multiple modes that can be selected with states. The default mode is run_mode
. In run_mode
, the NAU7802 takes a reading every two seconds. This value is converted to grams and ounces and is appended to the avg_read
array.
Once the length of avg_read
is greater than 10
, avg_read
is averaged. The return
is shown on the displays and then the process begins again. After this process runs 100
times, the scale prompts you to zero it out to retain accuracy.
The scale can show the weight in either ounces or grams, depending on whether show_oz
or show_grams
is True
.
# default run mode # checks NAU7802 every 2 seconds if run_mode is True and (time.monotonic() - clock) > 2: nau7802.channel = 1 value = read_raw_value() value = abs(value) - val_offset # takes value reading and divides with by the offset value # to get the weight in grams grams = value / calibration['offset_val'] oz = grams / 28.35 if show_oz is True: # append reading avg_read.append(oz) label = "oz" if show_grams is True: avg_read.append(grams) label = "g" if len(avg_read) > 10: the_avg = find_average(avg_read) display.print(" %0.1f %s" % (the_avg, label)) avg_read.clear() val_offset += 12 count += 1 if count > 100: count = 0 run_mode = False show_oz = False show_grams = False zero_out = True clock = time.monotonic()
Mode Select
If you press the green button, you get into mode select mode. This stops run_mode
and displays the mode options on the displays. You can press the green button to cycle through the options and press the blue button to select a mode.
# if you press the change mode button if (not green_btn.value and not green_btn_pressed) and run_mode: green.value = True # disables run mode (stops weighing) run_mode = False show_oz = False show_grams = False # mode is set to 0 mode = 0 # display shows the mode option display.print(mode_names[mode]) blue.value = True green_btn_pressed = True
Zeroing Mode
show_oz
and show_grams
change whether you're showing the weight in ounces or grams and goes back into run_mode
once they're selected.
zero_out
mode allows you to re-zero the NAU7802 at anytime. You'll be prompted to remove the weight from the scale, press the blue button and then zero_channel()
runs.
# if you select zero_out if (not blue_btn.value and not blue_btn_pressed) and mode == 2: # zero_out is set as the state # can zero out the scale without full recalibration zero_out = True blue.value = False mode = "run" blue_btn_pressed = True # if the zero_out state is true if zero_out and zero_stage == 0: blue_btn_pressed = True # clear the scale for zeroing display.fill(0) display.print("REMOVE ") zero_stage = 1 blue.value = True green.value = True if (not blue_btn.value and not blue_btn_pressed) and zero_stage == 1: green.value = False # updates display display.fill(0) display.print("ZEROING") blue.value = False # runs zero_channel() function on both channels nau7802.channel = 1 zero_channel() display.fill(0) display.print("ZEROED ") zero_out = False stage = 0 # goes into weighing mode val_offset = 0 run_mode = True show_oz = True label = "oz" display.print(" %0.1f %s" % (the_avg, label))
Show Offset Mode
By selecting show offset, the current offset_val
is displayed for 5
seconds. This is helpful for updating your calibration.py file and other troubleshooting.
# if you select the offset if (not blue_btn.value and not blue_btn_pressed) and mode == 4: # displays the curren offset value stored in the code blue.value = False display.fill(0) display.print("%0.4f" % calibration['offset_val']) time.sleep(5) mode = "run" # goes back to weighing mode show_oz = True label = "oz" display.print(" %0.1f %s" % (the_avg, label)) run_mode = True blue_btn_pressed = True
Calibration Mode
calibration_mode
lets you recalibrate the NAU7802 by running through the zero_channel()
function, calculateCalibration()
function with the scale zeroed, calculateCalibration()
function with the defined weight object on the scale and then finding the new offset_val
.
The steps of the process are advanced by button presses that trigger and increase the value of stage
. This ensures that the scale is prepped for each stage of the calibration.
calculateCalibration()
returns an average of the NAU7802's readings. The average of the scale with nothing on it (zero_avg
) and the average of the scale with the defined weight object (weight_avg
) are subtracted from each other and then divided by weight
. The result of that sets the new offset_val
.
# stage 5 if (not blue_btn.value and not blue_btn_pressed) and stage == 4: blue_btn_pressed = True blue.value = False display.fill(0) display.print("WEIGHING") weight_readings = [] # weighs the item 10 times, stores the readings in an array & averages them weight_avg = calculateCalibration(weight_readings) # calculates the new offset value calibration['offset_val'] = (weight_avg-zero_avg) / calibration['weight'] display.marquee("%0.2f - CALIBRATED " % calibration['offset_val'], 0.3, False) stage = 5 display.fill(0) display.print("DONE") blue.value = True