magnet-spinny-thing

Measuring the rpm of a spinning gear with magnetic sensor and Raspberry Pico

This project was done by Vannak (@Vlak23) in his Advanced Automation Class.

Upgrade to OLED Display and Raspberry Pico

On June 3rd the upgrade to the Pico with more memory finally worked. And the display plotted the rpm as well. Plus the plotter in Circuitpython printed the values continously.

Code

# https://github.com/Vlak23/magnet-spinny-thing
# Version 8.0  2022-06-04 
# adapted for Raspberry Pico and plotter output plus OLED display

import board
import busio
import displayio
import analogio
import digitalio
import terminalio
import time
from adafruit_display_text import label
import adafruit_displayio_sh1106

displayio.release_displays()

# Connect display via I2C
i2c = busio.I2C(board.GP17, board.GP16) # SCL SDA
display_bus = displayio.I2CDisplay(i2c, device_address=0x3C)
display = adafruit_displayio_sh1106.SH1106(display_bus, width=128, height=64)

# Make the display context
# splash = displayio.Group()
# display.show(splash)
print("Ready to start in 2 seconds, activate plotter")
time.sleep(2.0)

# Set up light sensor
light = analogio.AnalogIn(board.A1)

SAMPLE_PERIOD = 0.001 # seconds
SAMPLE_SIZE = 500 # number of measurements to analyze at a time


# Set up lists to use for analysis
raw_values = [0]*SAMPLE_SIZE
light_values = [0]*SAMPLE_SIZE
num_transitions = 0
time_of_rotation = 0.0
# This is a calibration step to figure out what threshold value to use.
# Press the button A value when the light sensor is dark
THRESHOLD = 53000

current_time = 0.0
elapsed_time = 0
start_time = time.monotonic()
stop_collecting = False
old_pulsetime = 0

# This starts the data collection loop.
while not stop_collecting:


    # Read the raw light value from the sensor
    raw_light = light.value
    # Add the light value to the list of raw values
    raw_values.append(raw_light)

    # Once enough data points have been collected, process the list of raw_values.

    if(len(raw_values)>= SAMPLE_SIZE):

        # Build a list  of thresholded values
        # When your code is working in Replit on your sample CSV, this is where you want to put your algorithm for processing.
        # Instead of going row by row through the CSV file, you want to go row by row through the list of raw values.
        for raw_light_value in raw_values:

            if(raw_light_value > THRESHOLD):
                light_value = 1
            else:
                light_value = 0
            light_values.append(light_value)

        # Go through the thresholded data and change the number of transitions whenever the values go from 0 to 1.
        for i in range(len(light_values)-1):
            if(light_values[i] == 0 and light_values[i+1] == 1):
                current_time = time.monotonic()
                time_of_rotation = current_time - old_pulsetime
                old_pulsetime = current_time
                num_transitions += 1
        RPM = num_transitions * 2 * 60
        #     if(time_of_rotation > 0):
#                 RPM = 60/time_of_rotation
#             else:
#                 RPM = 0
        num_transitions = 0
        # Update the elapsed time based on how much time has gone by, and then print the data
        elapsed_time += current_time - start_time
        #print("{0},{1}".format(elapsed_time,RPM))
        print("({0})".format(RPM))

        # Reset the lists of data for the next sample period.
        start_time = current_time
        raw_values = []
        light_values = []


    time.sleep(SAMPLE_PERIOD)

done.

More pictures