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
from os import getenv
import time
import json
import board
from digitalio import DigitalInOut, Direction, Pull
from adafruit_ht16k33.segments import Seg14x4
from cedargrove_nau7802 import NAU7802
from calibration import calibration
import rtc
import socketpool
import wifi
import adafruit_ntp
from adafruit_azureiot import IoTCentralDevice
# 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)
# Get WiFi details, ensure these are setup in settings.toml
ssid = getenv("CIRCUITPY_WIFI_SSID")
password = getenv("CIRCUITPY_WIFI_PASSWORD")
if None in [ssid, password]:
raise RuntimeError(
"WiFi settings are kept in settings.toml, "
"please add them there. The settings file must contain "
"'CIRCUITPY_WIFI_SSID', 'CIRCUITPY_WIFI_PASSWORD', "
"at a minimum."
)
print("Connecting to WiFi...")
wifi.radio.connect(ssid, password)
print("Connected to WiFi!")
# check system time
if time.localtime().tm_year < 2022:
print("Setting System Time in UTC")
pool = socketpool.SocketPool(wifi.radio)
ntp = adafruit_ntp.NTP(pool, tz_offset=-4)
# NOTE: This changes the system time so make sure you aren't assuming that time
# doesn't jump.
rtc.RTC().datetime = ntp.datetime
else:
print("Year seems good, skipping set time.")
# Create an IoT Central device client and connect
esp = None
pool = socketpool.SocketPool(wifi.radio)
device = IoTCentralDevice(
pool, esp, getenv("id_scope"), getenv("device_id"), getenv("device_primary_key")
)
display.fill(0)
display.print("DIALING*")
print("Connecting to Azure IoT Central...")
device.connect()
display.print("CONNECTD")
print("Connected to Azure IoT Central!")
device.disconnect()
print("Disconnected")
# 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
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)
# send data to azure with ounces and grams
def send_to_azure(current_oz, current_grams):
# turn on green LED
green.value = True
display.print("DIALING*")
# connect to azure
device.reconnect()
# turn on blue LED
blue.value = True
display.print("CONNECTD")
time.sleep(1)
display.print("SENDING!")
# send JSON of ounces and grams
message = {"Ounces": current_oz, "Grams": current_grams}
device.send_telemetry(json.dumps(message))
display.fill(0)
display.print("SENT!")
# disconnect and turn off LEDs
device.disconnect()
green.value = False
blue.value = False
# 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?", "TO AZURE"]
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 = []
avg_grams = []
avg_oz = []
values = []
val_offset = 0
avg_values = []
the_ounces = 0
the_grams = 0
# initial reading from the scale
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()
value = abs(value) - val_offset
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
avg_grams.append(grams)
avg_oz.append(oz)
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)
the_grams = find_average(avg_grams)
the_ounces = find_average(avg_oz)
display.print(" %0.1f %s" % (the_avg, label))
avg_read.clear()
avg_grams.clear()
avg_oz.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) % 6
# 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 (not blue_btn.value and not blue_btn_pressed) and mode == 5:
blue.value = False
display.fill(0)
# sends data to azure
send_to_azure(the_ounces, the_grams)
time.sleep(1)
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.
calibration.py File
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.
settings.toml
You will need to create and add a settings.toml file to your CIRCUITPY drive. Your settings.toml file will need to include the following information:
# This file is where you keep secret settings, passwords, and tokens! # If you put them in the code you risk committing that info or sharing it CIRCUITPY_WIFI_SSID="your-wifi-ssid" CIRCUITPY_WIFI_PASSWORD="your-wifi-password" id_scope="YOUR-AZURE-ID-SCOPE-HERE" device_id="YOUR-AZURE-DEVICE-ID-HERE" device_primary_key="YOUR-AZURE-DEVICE-PRIMARY-KEY-HERE"
You'll gather your ID scope, device ID and device primary key from your device connection groups page in your Azure application. Make sure to refer to the Connect Your Device page in this guide to see the process for accessing the keys.
How the CircuitPython Code Works
The CircuitPython code is identical to the original NAU7802 Food Scale CircuitPython code as far as scale functionality. This version of the code adds functionality for connecting to, and sending data to, Azure.
The code begins by connecting to WiFi and grabbing the date and time using the adafruit_ntp library.
# Get WiFi details, ensure these are setup in settings.toml
ssid = getenv("CIRCUITPY_WIFI_SSID")
password = getenv("CIRCUITPY_WIFI_PASSWORD")
if None in [ssid, password]:
raise RuntimeError(
"WiFi settings are kept in settings.toml, "
"please add them there. The settings file must contain "
"'CIRCUITPY_WIFI_SSID', 'CIRCUITPY_WIFI_PASSWORD', "
"at a minimum."
)
print("Connecting to WiFi...")
wifi.radio.connect(ssid, password)
print("Connected to WiFi!")
# check system time
if time.localtime().tm_year < 2022:
print("Setting System Time in UTC")
pool = socketpool.SocketPool(wifi.radio)
ntp = adafruit_ntp.NTP(pool, tz_offset=-4)
# NOTE: This changes the system time so make sure you aren't assuming that time
# doesn't jump.
rtc.RTC().datetime = ntp.datetime
else:
print("Year seems good, skipping set time.")
Then, a connection is established with Microsoft Azure. The alphanumeric display updates its text to show what is going on with the connection process.
# Create an IoT Central device client and connect
esp = None
pool = socketpool.SocketPool(wifi.radio)
device = IoTCentralDevice(
pool, esp, getenv("id_scope"), getenv("device_id"), getenv("device_primary_key")
)
display.fill(0)
display.print("DIALING*")
print("Connecting to Azure IoT Central...")
device.connect()
display.print("CONNECTD")
print("Connected to Azure IoT Central!")
The send_to_azure() function sends the current weight in ounces and grams to Azure with device.send_telemetry(json.dumps(message)). It also uses the buttons' LEDs and alphanumeric display to indicate the processes in the code.
# send data to azure with ounces and grams
def send_to_azure(current_oz, current_grams):
# turn on green LED
green.value = True
display.print("DIALING*")
# connect to azure
device.reconnect()
# turn on blue LED
blue.value = True
display.print("CONNECTD")
time.sleep(1)
display.print("SENDING!")
# send JSON of ounces and grams
message = {"Ounces": current_oz, "Grams": current_grams}
device.send_telemetry(json.dumps(message))
display.fill(0)
display.print("SENT!")
# disconnect and turn off LEDs
device.disconnect()
green.value = False
blue.value = False
Logging Ounces and Grams
The alphanumeric display shows either ounces or grams depending on the mode selected. In the background though, both the ounces and grams are logged in the_grams and the_ounces.
grams = value / calibration['offset_val']
oz = grams / 28.35
avg_grams.append(grams)
avg_oz.append(oz)
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)
the_grams = find_average(avg_grams)
the_ounces = find_average(avg_oz)
display.print(" %0.1f %s" % (the_avg, label))
avg_read.clear()
avg_grams.clear()
avg_oz.clear()
Send Weight to Azure
The food scale is coded to have a selection of mode functionality. One of the functions in the list is sending the data to Azure. If mode is 5 and the blue button is pressed, then send_to_azure(the_ounces, the_grams) is called and sends the current weigh in ounces and grams is sent to your Azure IoT Central application. Then, the scale goes back to weighing mode.
if (not blue_btn.value and not blue_btn_pressed) and mode == 5:
blue.value = False
display.fill(0)
# sends data to azure
send_to_azure(the_ounces, the_grams)
time.sleep(1)
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
Page last edited March 12, 2025
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