poll rate example

[relangford]

Would someone please write an example that changes the poll rate to a higher speed? I'm having trouble making it work. The only thing that has worked for me is to change the default in my local copy of cedargrove_nau7802.py.
Thanks!

[CedarGroveStudios]

Here's an example calibrator that measures raw output:

# clue_scale_calibrator.py

import time
import board
from cedargrove_nau7802 import NAU7802

SAMPLE_AVG = 3  # Number of sample values to average
DEFAULT_GAIN = 128  # Default gain for internal PGA
POLL_RATE = 320  # 10, 20, 40, 80, or 320

# Instantiate 24-bit load sensor ADC
i2c = board.I2C()  # uses board.SCL and board.SDA
# i2c = board.STEMMA_I2C()  # For using the built-in STEMMA QT connector on a microcontroller
nau7802 = NAU7802(i2c, address=0x2A, active_channels=1)


def zero_channel():
    """Initiate internal calibration and zero the current channel. Use after
    power-up, a new channel is selected, or to adjust for measurement drift.
    Can be used to zero the scale with a tare weight."""
    nau7802.calibrate("INTERNAL")
    nau7802.calibrate("OFFSET")


def read(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)


# Activate the NAU780 internal analog circuitry, set gain, and calibrate/zero
nau7802.enable(True)
nau7802.gain = DEFAULT_GAIN  # Use default gain
nau7802.poll_rate = POLL_RATE
zero_channel()  # Calibrate and zero

print("-----------------------------------")
print(" NAU7802 SINGLE CHANNEL CALIBRATOR")
print("-----------------------------------")
print("Place a calibration weight on the")
print("load cell.")
print("-----------------------------------")
print("")


# Main loop: Read sample and display value
while True:

    # Read the raw value; print raw value, gain setting, % of full-scale, and measured poll_rate
    t0 = time.monotonic()
    value = read(SAMPLE_AVG)
    rate = (1/(time.monotonic() - t0))
    print(f"CHAN_{nau7802.channel:1.0f} RAW VALUE: {value:7.0f}")
    print(f"GAIN: x{DEFAULT_GAIN}  full-scale: {(value / ((2**23) - 1)) * 100:3.2f}%")
    print(f"POLL_RATE: {rate:4.1f}")
    print("===================================")

    time.sleep(0.1)

Is this what you were looking for?

BTW, the measured sample rate is somewhat less than the value set in the code and doesn't exceed about 100SPS.

[relangford]

That appears to be exactly what I'm looking for. Thanks!

However, I'm only getting measured poll rates of 12-17SPS.

Why does the measured sample rate max out at 100SPS? And what can I do to get to that rate?

[CedarGroveStudios]

Can you share your code?

[relangford]

I ran your example above verbatim. The only thing is I ran it directly from my MacBook Pro using an Adafruit MCP2221 breakout board

Here is a bit of the output:

CHAN_1 RAW VALUE: 184
GAIN: x128 full-scale: 0.00%
POLL_RATE: 16.7

CHAN_1 RAW VALUE: 114
GAIN: x128 full-scale: 0.00%
POLL_RATE: 12.6

CHAN_1 RAW VALUE: 372
GAIN: x128 full-scale: 0.00%
POLL_RATE: 11.9

CHAN_1 RAW VALUE: -618
GAIN: x128 full-scale: -0.01%
POLL_RATE: 11.9

CHAN_1 RAW VALUE: 56
GAIN: x128 full-scale: 0.00%
POLL_RATE: 14.5

CHAN_1 RAW VALUE: 54
GAIN: x128 full-scale: 0.00%
POLL_RATE: 17.5

CHAN_1 RAW VALUE: 616
GAIN: x128 full-scale: 0.01%
POLL_RATE: 12.0

[CedarGroveStudios]

I've not used the MCP2221 General Purpose USB to GPIO ADC I2C - Stemma QT breakout, so I'm not certain of where to look for the speed bottleneck. The numbers I reported were from a standalone test with the NAU7802 breakout connected via stemmaQT to a Clue board -- no host connection. You may want to post the question on the Forums or the Adafruit Discord to cast a broader net.