The following example code will show you how use the PiCowbell Adalogger with CircuitPython to log data from a sensor to a file on an SD card with timestamps from the RTC module. In addition to a Raspberry Pi Pico and PiCowbell Adalogger, you will also need:
- CR1220 coin cell battery
- microSD card
- STEMMA QT cable
- MCP9808 Temperature Sensor
CircuitPython Microcontroller Wiring
Connect the Raspberry Pi Pico and PiCowbell Adalogger as described in the assembly pages. Next, insert a CR1220 battery into the coin cell battery holder on the PiCowbell Adalogger. Then, insert a microSD card into the PiCowbell Adalogger microSD card slot.
Finally, connect the MCP9808 STEMMA QT board to the PiCowbell Adalogger STEMMA QT port with a STEMMA QT cable.
CircuitPython Usage
To use with CircuitPython, you need to first install the necessary libraries into the lib folder on your CIRCUITPY drive. Then you need to update code.py with the example script.
Thankfully, we can do this in one go. In the example below, click the Download Project Bundle button below to download the necessary libraries and the code.py file in a zip file. Extract the contents of the zip file, and copy the entire lib folder and the code.py file to your CIRCUITPY drive.
Your CIRCUITPY/lib folder should contain the following folders and files:
- /adafruit_bus_device
- /adafruit_register
- adafruit_mcp9808.mpy
- adafruit_pcf8523.mpy
# SPDX-FileCopyrightText: 2023 Liz Clark for Adafruit Industries
#
# SPDX-License-Identifier: MIT
"""CircuitPython PiCowbell Adalogger Example"""
import time
import board
import sdcardio
import busio
import storage
import adafruit_mcp9808
from adafruit_pcf8523.pcf8523 import PCF8523
# setup for Pico I2C
i2c = busio.I2C(board.GP5, board.GP4)
# setup for mcp9808 temp monitor
mcp9808 = adafruit_mcp9808.MCP9808(i2c)
# setup for RTC
rtc = PCF8523(i2c)
# list of days to print to the text file on boot
days = ("Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday")
# SPI SD_CS pin
SD_CS = board.GP17
# SPI setup for SD card
spi = busio.SPI(board.GP18, board.GP19, board.GP16)
sdcard = sdcardio.SDCard(spi, SD_CS)
vfs = storage.VfsFat(sdcard)
try:
storage.mount(vfs, "/sd")
print("sd card mounted")
except ValueError:
print("no SD card")
# to update the RTC, change set_clock to True
# otherwise RTC will remain set
# it should only be needed after the initial set
# if you've removed the coincell battery
set_clock = False
if set_clock:
# year, mon, date, hour, min, sec, wday, yday, isdst
t = time.struct_time((2023, 3, 6, 00, 00, 00, 0, -1, -1))
print("Setting time to:", t)
rtc.datetime = t
print()
# variable to hold RTC datetime
t = rtc.datetime
time.sleep(1)
def get_temp(sensor):
temperature_celsius = sensor
temperature_fahrenheit = temperature_celsius * 9 / 5 + 32
return temperature_fahrenheit
# initial write to the SD card on startup
try:
with open("/sd/temp.txt", "a") as f:
# writes the date
f.write('The date is {} {}/{}/{}\n'.format(days[t.tm_wday], t.tm_mon, t.tm_mday, t.tm_year))
# writes the start time
f.write('Start time: {}:{}:{}\n'.format(t.tm_hour, t.tm_min, t.tm_sec))
# headers for data, comma-delimited
f.write('Temp,Time\n')
# debug statement for REPL
print("initial write to SD card complete, starting to log")
except ValueError:
print("initial write to SD card failed - check card")
while True:
try:
# variable for RTC datetime
t = rtc.datetime
# append SD card text file
with open("/sd/temp.txt", "a") as f:
# read temp data from mcp9808
temp = get_temp(mcp9808.temperature)
# write temp data followed by the time, comma-delimited
f.write('{},{}:{}:{}\n'.format(temp, t.tm_hour, t.tm_min, t.tm_sec))
print("data written to sd card")
# repeat every 30 seconds
time.sleep(30)
except ValueError:
print("data error - cannot write to SD card")
time.sleep(10)
Once everything is saved to the CIRCUITPY drive, connect to the serial console to see status information from the code.
In the example, the microSD card is mounted and the file temp.txt is created to log temperature data from the MCP9808. Then in the loop, a temperature reading is taken and saved to temp.txt, along with the timestamp from the RTC module, every 30 seconds. Every time data is written to the file, data written to the sd card is written to the REPL to let you know that the code is running properly.
After logging data to the file, you can open temp.txt from the microSD card to see your data.
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