Monk Makes Plant Monitor

This documents a Python library for the Monk Makes Plant Monitor (MMPM) connected to a BBC micro:bit through the micro:bit Python Editor over a serial connection.

Assumptions

• The MMPM communicates over a two-way serial link at 9600bps, N81 protocol on two unused pins. This code assumes TX on pin8 and RX on pin9. (The only pins on a micro:bit v2 that are unused by other micro:bit functions are pin0, pin1, pin2, pin8, pin9, and pin16.)
• In order to use the micro:bit on-line serial terminal that, ‘…shows errors and other output from the program running on your micro:bit’ so the ‘…program can print messages using the print function,’ the UART must be set to its default settings with uart.init(115200). However, the MMPM also communicates serially using the UART, so it must also be initialized before use.
• The three commands used to read the three sensors are 'h', 't', and 'w'. There are other commands ('j', 'L', 'l', and 'v') that are unused by this library. The command summary is:

Command	Delay	Units	Notes
'h'	100ms	% ± 2%	relative humidity
't'	100ms	°C	temperature
'w'	1000ms	%	moisture

• The connector J3 has 5 connections, with both clippable through-hole connections and a 0.1” pin header. The pins are:

Pin	Signal	I/O	Notes
1	PA6/D2/DAC	O	analog moisture (25mV / %)
2	TxD	O	transmit data
3	RxD	I	receive data
4	+3V	+V	+3V
5	GND	⏚	0V

Code

# Imports go at the top
from microbit import *

delay= 10
pm_init = lambda: uart.init(9600, 8, None, 1, tx=pin8, rx=pin9)
py_init = lambda: uart.init(115200)

def read_data(delay=delay):
    """Returns a dictionary with data readings of humidity, temperature,
    and moisture read over a serial connection from a Monk Makes Plant
    Monitor. An example return is: {'h': 48.43, 'w': 38.0, 't': 23.56}.
    The value types will be float. If a ValueError is generated from
    the uart.readline text, the commands are repeated until all results
    are good. The UART is set to 9600 8N1 on pins 8 & 9."""
    pm_init()
    res, ret = dict(), ''
    # Process 'h', 't', & 'w' commands until all responses are float.
    while not(res and all(type(val) is float for val in res.values())):
        # Process commands for humidity, temperature, and wetness.
        for cmd, slp in {'h': 100, 't': 100, 'w': 1000}.items():
            uart.write(cmd)
            sleep(max(slp, delay))   # slp response time from datasheet
            while not ret:
                ret = uart.readline()
            # ret must be of the form 'h=48.43\n', otherwise ValueError.
            try:
                key, val = str(ret, 'utf-8').strip().split('=')
                res[key], ret = float(val), ''
            except ValueError as e:
                res[cmd], ret = e, ''
    sleep(delay)
    return res

def echo_data(data, delay=delay):
    """Setup UART to default (115200) and print data."""
    py_init()
    print(data)
    sleep(delay)

# Code in a 'while True:' loop repeats forever
while True:
    data = read_data()
    echo_data(data)
    if button_a.is_pressed(): break

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Links

Link	Description
https://monkmakes.com/​	‘Founded in 2013, Monk Makes Ltd designs and manufacturers a wide range of electronics kits and circuit boards from its base in the North West of England.’
https://monkmakes.com/​pmon	Plant Monitor website
https://www.adafruit.com/​product/​5587	Plant Monitor is available at adafruit
https://monkmakes.com/​downloads/​datasheet_plant_monitor.pdf	Plant Monitor datasheet
https://github.com/​monkmakes/​plant_monitor_firmware	Plant Monitor firmware
https://tech.microbit.org/​hardware/​edgeconnector/​	micro:bit pinouts
https://microbit-micropython.readthedocs.io/​en/​v2-docs/​uart.html	micro:bit UART
https://ww1.microchip.com/​downloads/​en/​DeviceDoc/​ATtiny1614-16-17-DataSheet-DS40002204A.pdf	ATTiny 1614 — the µcontroller
https://docs.python.org/​3.4/​	Python 3.4 documentation

#microbit #embedded #Python