Get the code from GitHub, place it in Mu and save it onto the Circuit Playground Express as code.py (not cold.py).
# SPDX-FileCopyrightText: 2018 Anne Barela for Adafruit Industries
#
# SPDX-License-Identifier: MIT
import time
import board
from analogio import AnalogIn
from adafruit_crickit import crickit
import neopixel
print("Peltier Module Demo")
pixels = neopixel.NeoPixel(board.NEOPIXEL, 10, auto_write=False)
def show_value(time_val): # Show time on NeoPixels on CPX
num_pixels = int(10-time_val)
for i in range(num_pixels):
pixels[i] = (10*(i+1), 0, 0)
for i in range(num_pixels, 10):
pixels[i] = (0, 0, 0)
pixels.show()
TMP36 = AnalogIn(board.A3) # TMP36 connected to A3, power & ground
POT = AnalogIn(board.A7) # potentiometer connected to A7, power & ground
peltier = crickit.dc_motor_2 # Drive the Peltier from Motor 2 Output
while True: # Loop forever
voltage = TMP36.value * 3.3 / 65536.0
tempC = (voltage - 0.5) * 100.0
tempF = (tempC * 9.0 / 5.0) + 32.0
cool_value = POT.value / 6553.6 # convert 0.0 to 10.0
# timing can be zero or can be 1 second to 10 seconds
# between 0 and 1 is too short a time for a Peltier module
if cool_value < 0.2:
cool_value = 0.0
if 1.0 > cool_value >= 0.2:
cool_value = 1.0
print((tempF, cool_value)) # Show in REPL
show_value(cool_value) # Show on NeoPixels
# Peltier cannot be PWM - either off or on
# Use potentiometer read to set seconds b
if cool_value > 0:
peltier.throttle = 0.0 # turn off
time.sleep(cool_value) # wait
peltier.throttle = 1.0 # turn on
time.sleep(10.0 - cool_value) # wait
If the potentiometer is not fully "off " (to left) you should see some NeoPixels on telling you roughly how many seconds the Peltier module is cycled on. Zero is fully off, ten lights fully on.
Using Mu, you can plot the data and see the values in the Serial monitor. The logging is slower than in the Hot example due to the slow cycling of the Peltier module compared to the heating pad.
Be sure the TMP36 sensor is in good thermal contact with the cold side of the module.
