A simple version of the CircuitPython soil moisture code in https://www.instructables.com/Soil-Moisture-Sensing-With-the-Maker-Pi-Pico/

Author: Kevin J Walters

microbit/mb-soil-moisture.py

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+### mb-soil-moisture.py v1.0
+### Show soil moisture on micro:bit display using resistive and capacitive sensors
+
+### Tested with BBC micro:bit v1.5 and MicroPython v1.9.2-34-gd64154c73
+
+### MIT License
+
+### Copyright (c) 2021 Kevin J. Walters
+
+### Permission is hereby granted, free of charge, to any person obtaining a copy
+### of this software and associated documentation files (the "Software"), to deal
+### in the Software without restriction, including without limitation the rights
+### to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+### copies of the Software, and to permit persons to whom the Software is
+### furnished to do so, subject to the following conditions:
+
+### The above copyright notice and this permission notice shall be included in all
+### copies or substantial portions of the Software.
+
+### THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+### IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+### FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+### AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+### LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+### OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+### SOFTWARE.
+
+
+### This is a micro:bit version of
+### https://github.com/kevinjwalters/circuitpython-examples/blob/master/pico/soil-moisture.py
+### featured in
+### https://www.instructables.com/Soil-Moisture-Sensing-With-the-Maker-Pi-Pico/
+
+import utime
+from microbit import display, pin0, pin1, sleep
+
+RES_PIN = pin0
+CAP_PIN = pin1
+
+### Values for (dry, wet) based on values from CircuitPython version
+RES_RANGE = (1023, 156)
+CAP_RANGE = (593, 343)
+
+### The BBC micro:bit 5x5 LED display can show ten
+### brightness levels in MicroPython 0-9
+### (The underlying DAL supports a wider range 0-255)
+MAX_BRIGHTNESS = 9
+
+
+def bar_chart(value,
+              columns=(0, 1, 2, 3, 4),
+              *, max_value=100):
+    """Draw a vertical bar chart based on percentage value
+       using variable brightness levels on display."""
+
+    ### Nine brightness levels on 5x5 LED matrix equates
+    ### to 45 pixel steps - start at bottow row (no 4) and
+    ### light pixels until value px_steps value is reached
+    px_steps = round(value * 45 / max_value)
+    for y in range(4, -1, -1):
+        for x in columns:
+            ### The min/max here limit values from 0 to 9
+            display.set_pixel(x, y,
+                              min(MAX_BRIGHTNESS, max(0, px_steps)))
+        px_steps -= MAX_BRIGHTNESS
+
+
+def adc_to_moisture(raw_adc, arid_value, sodden_value):
+    """Convert a micro:bit 0-1024 ADC value into a moisture percentage
+       using crude linear model."""
+
+    a_lower = min(arid_value, sodden_value)
+    a_range = abs(sodden_value - arid_value)
+    inverted = arid_value > sodden_value
+
+    fraction = (raw_adc - a_lower) / a_range
+    if inverted:
+        fraction = 1.0 - fraction
+
+    return min(100.0, max(0.0, fraction * 100.0))
+
+
+def get_res_moisture():
+    return adc_to_moisture(RES_PIN.read_analog(), *RES_RANGE)
+
+def get_cap_moisture():
+    return adc_to_moisture(CAP_PIN.read_analog(), *CAP_RANGE)
+
+
+scroll_delay=250   ### default is 150ms
+
+while True:
+    ### Read both values and display them slowly
+    res_perc = get_res_moisture()
+    cap_perc = get_cap_moisture()
+    display.scroll("R " + str(round(res_perc)),
+                   delay=scroll_delay)
+    sleep(2000)
+    display.scroll("C " + str(round(cap_perc)),
+                   delay=scroll_delay)
+    sleep(2000)
+
+    ### Now show both values on bar charts for 20 seconds
+    ### but only read fresh capacitive values
+    start_time_ms = utime.ticks_ms()
+    while True:
+        cap_perc = get_cap_moisture()
+        bar_chart(res_perc, (0, 1))  ### Left two columns
+        bar_chart(cap_perc, (3, 4))  ### Right two columns
+        now_time_ms = utime.ticks_ms()
+        if utime.ticks_diff(now_time_ms, start_time_ms) > 20000:
+            break
+        sleep(500)