SCD41 CO2 sensor example

examples/co2.py

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+"""
+Add a SCD41 sensor breakout to Presto to make a handy CO2 detector!
+https://shop.pimoroni.com/products/scd41-co2-sensor-breakout
+Touch and hold the screen to reset the high/low values.
+
+You will need the osansb.af font saved to your Presto alongside this script.
+"""
+
+import gc
+import time
+
+from presto import Presto
+from pimoroni_i2c import PimoroniI2C
+import breakout_scd41
+from picovector import Transform, Polygon, PicoVector, ANTIALIAS_X16
+
+i2c = PimoroniI2C(sda=40, scl=41)
+
+presto = Presto(full_res=True)
+display = presto.display
+vector = PicoVector(display)
+
+WIDTH, HEIGHT = display.get_bounds()
+
+t = Transform()
+vector.set_font_letter_spacing(100)
+vector.set_font_word_spacing(100)
+vector.set_font_line_height(110)
+vector.set_transform(t)
+
+BLACK = display.create_pen(0, 0, 0)
+WHITE = display.create_pen(216, 216, 200)
+RED = display.create_pen(127, 0, 0)
+GREEN = display.create_pen(0, 127, 0)
+
+# pick what bits of the colour wheel to use (from 0-360°)
+# https://www.cssscript.com/demo/hsv-hsl-color-wheel-picker-reinvented/
+CO2_HUE_START = 100  # green
+CO2_HUE_END = 0  # red
+TEMPERATURE_HUE_START = 240
+TEMPERATURE_HUE_END = 359
+HUMIDITY_SATURATION_START = 0
+HUMIDITY_SATURATION_END = 360
+
+# the range of readings to map to colours (and scale our graphs to)
+# https://www.kane.co.uk/knowledge-centre/what-are-safe-levels-of-co-and-co2-in-rooms
+CO2_MIN = 300
+CO2_MAX = 2000
+TEMPERATURE_MIN = 10
+TEMPERATURE_MAX = 33
+HUMIDITY_MIN = 10
+HUMIDITY_MAX = 90
+# use these to draw indicator lines on the CO2 graph
+OK_CO2_LEVEL = 800
+BAD_CO2_LEVEL = 1500
+
+MAX_READINGS = 120  # how many readings to store (and draw on the graph)
+
+# the areas of the screen we want to draw our graphs into
+CO2_GRAPH_TOP = HEIGHT * 0.2
+CO2_GRAPH_BOTTOM = HEIGHT * 0.75
+TEMPERATURE_GRAPH_TOP = HEIGHT * 0.75
+TEMPERATURE_GRAPH_BOTTOM = HEIGHT
+HUMIDITY_GRAPH_TOP = HEIGHT * 0.75
+HUMIDITY_GRAPH_BOTTOM = HEIGHT
+PADDING = 5
+
+LINE_THICKNESS = 3  # thickness of indicator and graph lines
+
+
+def graph_polygon(top, bottom, graph_min, graph_max, readings, y_offset=0):
+    # function to generate a filled graph polygon and scale it to the available space
+    points = []
+    reading_width = (WIDTH - 1) / max((len(readings) - 1), 1)
+    for r in range(len(readings)):
+        x = round(r * reading_width)
+        y = round(bottom + ((readings[r] - graph_min) * (top - bottom) / (graph_max - graph_min)))
+        points.append((x, y))
+    points.append((WIDTH - 1, round(bottom)))
+    points.append((0, round(bottom)))
+    if y_offset != 0:
+        for r in range(len(readings)):
+            x = round(r * reading_width)
+            y = round(bottom + ((readings[r] - graph_min) * (top - bottom) / (graph_max - graph_min)) + y_offset)
+            points.append((x, y))
+        points.append((WIDTH - 1, round(bottom)))
+        points.append((0, round(bottom)))    
+    poly = Polygon()
+    poly.path(*points)
+    return poly
+
+
+def line_polygon(top, bottom, min, max, value):
+    # function to generate a straight line on our graph at a specific value
+    points = []
+    points.append((0, round(bottom + ((value - min) * (top - bottom) / (max - min)))))
+    points.append((WIDTH, round(bottom + ((value - min) * (top - bottom) / (max - min)))))
+    points.append((WIDTH, round(bottom + ((value - min) * (top - bottom) / (max - min))) + LINE_THICKNESS))
+    points.append((0, round(bottom + ((value - min) * (top - bottom) / (max - min))) + LINE_THICKNESS))
+    poly = Polygon()
+    poly.path(*points)
+    return poly
+
+
+highest_co2 = 0.0
+lowest_co2 = 4000.0
+co2_readings = []
+temperature_readings = []
+humidity_readings = []
+
+# set up
+vector.set_antialiasing(ANTIALIAS_X16)
+vector.set_font("osansb.af", 50)
+display.set_pen(WHITE)
+
+try:
+    breakout_scd41.init(i2c)
+    breakout_scd41.start()
+    vector.text("Waiting for sensor to be ready", 0, 0)
+    display.update()
+except RuntimeError as e:
+    print(e)
+    vector.text("SCD41 breakout not detected :(", 0, 0)
+    vector.text("but you could buy one at pimoroni.com ;)", 0, HEIGHT - 120)
+    display.update()
+
+while True:
+    if presto.touch.state:
+        # reset recorded high / low values
+        highest_co2 = 0.0
+        lowest_co2 = 4000.0
+
+    if breakout_scd41.ready():
+        # read the sensor
+        co2, temperature, humidity = breakout_scd41.measure()
+
+        # if lists are empty, populate the list with the current readings
+        if len(co2_readings) == 0:
+            for i in range(MAX_READINGS):
+                co2_readings.append(co2)
+                temperature_readings.append(temperature)
+                humidity_readings.append(humidity)
+
+        # update highest / lowest values
+        if co2 < lowest_co2:
+            lowest_co2 = co2
+        if co2 > highest_co2:
+            highest_co2 = co2
+
+        # calculates some colours from the sensor readings
+        co2_hue = max(0, CO2_HUE_START + ((co2 - CO2_MIN) * (CO2_HUE_END - CO2_HUE_START) / (CO2_MAX - CO2_MIN)))
+        temperature_hue = max(0, TEMPERATURE_HUE_START + ((temperature - TEMPERATURE_MIN) * (TEMPERATURE_HUE_END - TEMPERATURE_HUE_START) / (TEMPERATURE_MAX - TEMPERATURE_MIN)))
+        humidity_hue = max(0, HUMIDITY_SATURATION_START + ((humidity - HUMIDITY_MIN) * (HUMIDITY_SATURATION_END - HUMIDITY_SATURATION_START) / (HUMIDITY_MAX - HUMIDITY_MIN)))
+
+        # keep track of readings in a list (so we can draw the graph)
+        co2_readings.append(co2)
+        temperature_readings.append(temperature)
+        humidity_readings.append(humidity)
+
+        # we only need to save a screen's worth of readings, so delete the oldest
+        if len(co2_readings) > MAX_READINGS:
+            co2_readings.pop(0)
+        if len(temperature_readings) > MAX_READINGS:
+            temperature_readings.pop(0)
+        if len(humidity_readings) > MAX_READINGS:
+            humidity_readings.pop(0)
+
+        # clear to black
+        display.set_pen(BLACK)
+        display.clear()
+
+        # draw the graphs and text
+        # draw the CO2 graph
+        display.set_pen(display.create_pen_hsv(co2_hue / 360, 1.0, 1.0))
+        co2_graph = graph_polygon(CO2_GRAPH_TOP, CO2_GRAPH_BOTTOM, CO2_MIN, CO2_MAX, co2_readings)
+        vector.draw(co2_graph)
+        # draw the CO2 indicator lines
+        display.set_pen(RED)
+        vector.draw(line_polygon(CO2_GRAPH_TOP, CO2_GRAPH_BOTTOM, CO2_MIN, CO2_MAX, BAD_CO2_LEVEL))
+        display.set_pen(GREEN)
+        vector.draw(line_polygon(CO2_GRAPH_TOP, CO2_GRAPH_BOTTOM, CO2_MIN, CO2_MAX, OK_CO2_LEVEL))
+        # draw the CO2 text
+        vector.set_font_size(40)
+        display.set_pen(WHITE)
+        vector.text(f"CO2: {co2:.0f}ppm", PADDING, 25)
+        display.set_pen(BLACK)
+        vector.set_font_size(30)
+        vector.text(f"Low {lowest_co2:.0f}ppm", PADDING, round(TEMPERATURE_GRAPH_TOP) - 12)
+        high_text = f"High {highest_co2:.0f}ppm"
+        text_width = int(vector.measure_text(high_text)[2])
+        vector.text(high_text, WIDTH - PADDING - text_width, round(TEMPERATURE_GRAPH_TOP) - 12)
+
+        # draw the humidity graph
+        # here we're using the 'hue' value to affect the saturation (so light blue to dark blue)
+        display.set_pen(display.create_pen_hsv(240 / 360, humidity_hue / 360, 1.0))
+        # draw this polygon twice, applying an offset to make a line rather than a filled shape
+        humidity_graph = graph_polygon(HUMIDITY_GRAPH_TOP, HUMIDITY_GRAPH_BOTTOM, HUMIDITY_MIN, HUMIDITY_MAX, humidity_readings, LINE_THICKNESS)
+        vector.draw(humidity_graph)
+        #display.set_pen(WHITE)
+        humidity_text = f"{humidity:.0f}% Humidity"
+        text_width = int(vector.measure_text(humidity_text)[2])
+        vector.text(humidity_text, WIDTH - PADDING - text_width, int(HUMIDITY_GRAPH_BOTTOM) - 13)
+
+        # draw the temperature graph
+        display.set_pen(display.create_pen_hsv(temperature_hue / 360, 1.0, 1.0))
+        # draw this polygon twice, applying an offset to make a line rather than a filled shape
+        temperature_graph = graph_polygon(TEMPERATURE_GRAPH_TOP, TEMPERATURE_GRAPH_BOTTOM, TEMPERATURE_MIN, TEMPERATURE_MAX, temperature_readings, LINE_THICKNESS)
+        vector.draw(temperature_graph)
+        #display.set_pen(WHITE)
+        vector.text(f"Temp: {temperature:.0f}°C", PADDING, int(TEMPERATURE_GRAPH_BOTTOM) - 13)
+
+        presto.update()
+
+    gc.collect()
+    time.sleep(0.5)