Raspberry Pi hd44780 with i2c LCD displaying performance

This is the final product:

The display will show the status of the raid array, and will show the current percentage load of the CPU and the memory.

First follow either of these guides:

circuitbasics.com: Raspberry Pi I2C LCD Set-up and Programming

tutorials-raspberrypi.com: Control a Raspberry Pi HD44780 LCD Display via I2C

This will go over the needed libraries (i2c_lib.py and lcddriver.py).

The script runs as a systemd service (lcdshowstatus.service), so it restarts automatically if it ever crashes - it's no longer scheduled via cron. Deploys are pushed straight from git to a bare repo on the Pi with a post-receive hook that checks out the new code and restarts the service.

This is the script to display the stats:

import logging
import subprocess
from time import sleep

import lcddriver
import psutil

# This script will display the status of the raid array, in use memory and CPU load on the lcd screen.
# The LCD has two lines, so the script will display the raid status on the first line and the memory and CPU load on the second line.
# The script will run in an infinite loop, updating the status every 60 seconds.
# The script will use the mdadm command to get the raid status and psutil to get the memory and CPU load.

logging.basicConfig(
    filename='/var/log/lcdshowstatus.log',
    level=logging.INFO,
    format='%(asctime)s %(levelname)s %(message)s',
)
logger = logging.getLogger(__name__)


def get_raid_state():
    """Return the mdadm State line, or a fallback string if it can't be read."""
    try:
        output = subprocess.check_output(['mdadm', '-D', '/dev/md0'], stderr=subprocess.STDOUT)
        output = output.decode('utf-8').split("\n")
        for line in output:
            if "State :" in line:
                return line.strip()
        logger.warning("mdadm output had no 'State :' line: %r", output)
    except (subprocess.CalledProcessError, FileNotFoundError, OSError) as exc:
        logger.error("Failed to read raid state: %s", exc)
    return "State: unknown"


def main():
    lcd = lcddriver.lcd()
    lcd.lcd_clear()
    logger.info("lcdshowstatus started")
    while True:
        state = get_raid_state()
        mem = psutil.virtual_memory()
        lcd.lcd_clear()
        lcd.lcd_display_string(state, 1)
        lcd.lcd_display_string("Mem:" + str(int(mem.percent)) + "% CPU:" + str(int(psutil.cpu_percent())) + "%", 2)
        sleep(60)


if __name__ == '__main__':
    try:
        main()
    except Exception:
        logger.exception("lcdshowstatus crashed")
        raise

Earlier versions had no error handling around the mdadm parsing and no logging, so a crash (with nothing to restart it) could leave the display frozen on a half-written frame. get_raid_state() now falls back to a safe value instead of crashing, everything logs to /var/log/lcdshowstatus.log, and systemd restarts the process if it ever does crash.

The full project is also available on Github. The needed libraries that work with this code are included.