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The principle CircuitPython code module, code.py, prepares and operates the Clue Espresso Scale. Earlier than utilizing the dimensions, you’ll have to replace code.py with a calibration ratio that’s distinctive to the load cell you connected to the NAU7802 breakout. First let’s take a stroll by the code and have a look at how every part works.
8a. Import and set defaults
This part imports all of the wanted modules and libraries, together with the NAU7802 sensor driver. After importing, the primary seen activity of this part is to show the Clue board’s NeoPixel LED yellow to point that the Espresso Scale is initializing. Throughout operation, the indicator LED will glow inexperienced when working usually or pink when zeroing the dimensions.
Subsequent, the dimensions defaults are specified. These are constants with names which might be capitalized to assist establish them as constants. You possibly can change these values to change the operation of the dimensions:
MAX_GR is the full-scale worth of the dimensions in grams. The tick mark values adjoining to the graduated scale graphic are routinely derived from MAX_GR which might be any constructive integer worth. For the reason that graduated scale graphic is split into tenths of full-scale, with 5 numbered tick marks, it’s finest to decide on an integer MAX_GR worth that can show properly comparable to 1000, 500, 250, 100, 50, 25, 10, or 5.
DEFAULT_GAIN is the achieve setting of the NAU7802 inner ADC’s incoming sign pre-amplifier. Usually, that is set to the very best worth of 128.
SAMPLE_AVG specifies the variety of measurements which might be averaged when the load cell is measured. The measurement worth will likely be extra secure with a excessive SAMPLE_AVG worth. The show will replace extra slowly with a better worth; it’s a trade-off between stability and velocity.
8b. Load cell calibration ratio
CALIB_RATIO is the issue that’s used to transform the NAU7802’s uncooked measurement worth into grams. This ratio will should be up to date after working the calibrator technique to your explicit load cell in Step 9 under. It is best to solely must measure and document this calibration ratio as soon as.
8c. Instantiate the sensor and show
The NAU7802 board is related to the Clue’s I2C bus and lives at handle 42 (hexadecimal 2A). The NAU7802 24-bit ADC chip is able to supporting two load cell channels, however solely the primary channel is out there on the Adafruit Stemma breakout board; active_channels is due to this fact set to 1.
Subsequent, the Clue’s built-in show is instantiated together with the first displayio graphics group layer, scale_group, which is able to include the background bitmap picture and different show layers.
Font objects for displaying measurement values and the tick mark labels are outlined subsequent.
8d. Show the background bitmap picture
Determine U
The show background file that features the graduated scale (Determine U) is learn from the Clue root listing and is appended as the primary merchandise within the main displayio group layer. All different graphics objects will likely be placed on layers over this background.
8e. Outline and show textual content and graphics
This part defines the graphic parts that will likely be positioned in entrance of the background graphic. First, the zeroing button graphic is appended to the first displayio group.
The subsection that begins with for i in vary… is the code that steps by the graduated scale’s tick marks, creating a price label that’s calculated utilizing the MAX_GR fixed and appending every label to the displayio group. Measurement values and items labels are added subsequent.
Lastly, the indicator_group with its floating indicator bubble is created and added to the first displayio group. The indicator_group layer is now the front-most graphics layer of the show (Determine V).
The indicator bubble is a yellow circle that travels up and down the graduated scale, pointing to the measured worth. The middle of the circle will usually be clear, however will seem yellow or pink relying on the dimensions’s present standing; yellow when initializing, pink when zeroing.
8f. Helpers
Two helper capabilities work with the NAU7802 driver class to zero the dimensions and to learn the load cell’s present uncooked worth:
The zero_channel( ) helper units up and zeros the NAU7802’s inner amplifiers and ADC (analog to digital converter) to arrange it to obtain alerts. This operate is used when the dimensions is first powered up, and when it’s manually zeroed by urgent the Clue board’s A button.
The load cell’s uncooked measurement worth is obtained by the learn( ) helper. This helper accepts an integer parameter that specifies the variety of samples to be averaged every time the helper is known as, defaulting to 1 pattern (no averaging). The helper returns the averaged uncooked measurement worth. Averaging the uncooked worth can assist scale back the jitter of the displayed worth.
8g. Activate sensor and put together to loop
That is the place the NAU7802 ADC is enabled and calibrated to be used. Earlier than calibrating and zeroing, the inner sensor amplifier’s achieve is ready to the default worth. As soon as accomplished, the Clue will chirp some welcoming notes.
8h. The first code loop
The first loop is the primary operational technique of the dimensions. The loop signifies the dimensions’s standing on the Clue board’s NeoPixel; inexperienced when the dimensions is working, pink when it’s busy zeroing.
After setting the NeoPixel coloration, the load cell uncooked worth is measured and transformed to grams and ounces. The transformed values are formatted and positioned into the corresponding on-screen show labels and are additionally printed within the REPL.
The grams measurement worth is used to place the on-screen indicator bubble alongside the graduated scale graphic utilizing the map_range( ) operate. Additionally, if the grams measurement worth falls outdoors of the minimal or most vary, the bubble is “parked” on the excessive place and its inside coloration is modified from clear to pink.
Lastly, the Clue board’s A button is watched to see if it was pressed. When pressed, the Clue performs a sound and can start zeroing the dimensions. Through the zeroing course of, the NeoPixel, the zeroing button graphic, and the middle of the bubble are all set to a pink coloration. After zeroing has accomplished, the code waits till the button is launched earlier than enjoying a completion sound, setting the bubble and zeroing button graphic interiors to clear, and returning the Clue Espresso Scale to regular operation.
# The Major Code Loop
# Learn sensor, transfer bubble, show values
whereas True:
clue.pixel[0] = clue.GREEN # Set standing
indicator to inexperienced (prepared)
# Learn the uncooked scale worth and scale for
grams and ounces
worth = learn(SAMPLE_AVG)
mass_grams = spherical(worth * CALIB_RATIO, 1)
mass_ounces = spherical(mass_grams * 0.03527, 2)
grams_value.textual content = f”{mass_grams:5.1f}”
ounces_value.textual content = f”{mass_ounces:5.2f}”
print(f” {grams_value.textual content} grams
{ounces_value.textual content} ounces”)
# Reposition the indicator bubble based mostly
on grams worth
min_gr = (MAX_GR // 5) * –1 # Minimal
show worth
bubble.y = int(map_range(mass_grams,
min_gr, MAX_GR, 240, 0)) – 10
if mass_grams > MAX_GR or mass_grams <
min_gr:
bubble.fill = clue.RED
else:
bubble.fill = None
# Verify to see if zeroing button is pressed
if clue.button_a:
# Zero the sensor
clue.pixel[0] = clue.RED # Set
standing indicator to pink (stopped)
bubble.fill = clue.RED # Set bubble
middle to pink (stopped)
zero_button_circle.fill = clue.RED #
Set to pink (stopped)
clue.play_tone(1660, 0.3) # Play
“button pressed” tone
zero_channel()
whereas clue.button_a:
# Wait till button is launched
time.sleep(0.1)
clue.play_tone(1440, 0.5) # Play
“reset accomplished” tone
zero_button_circle.fill = None # Set
to clear (prepared)
bubble.fill = None # Set bubble
middle to clear (prepared)
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