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Micro:Bit Temperature Display Tutorial

Tutorial Aim:

To display a TMP36 temperature sensor reading on a Robot:Bit v2 by continuously polling every 10 seconds and converting the analog reading from the temperature pin to Celsius using:

temp(Celsius) = (voltage - 500) / 10

Requirements:

This tutorial makes use of the Micro:bit Electronics Learning Package

  • Microsoft MakeCode for micro:bit
  • Micro:bit V2
  • Micro:bit Robot:bit Expansion Shield V2
  • Breakout Board
  • 3 FM Jumper Wires
  • TMP36 temperature sensor

Pin Layout:

Micro:Bit Pins:Sensor Pins:
GNDGND
3.3VVCC
0OUT

 

Setup:

Please refer to the diagram below for wiring. Please note that the circuit diagram uses a different Micro:bit shield than the supplied in our package, despite this, the wiring is the same.

  •  Place the TMP36 temperature sensor on the breakout board and use the FM jumper wires to connect it to pin 0 on the Micro:bit 
  • Open Microsoft Makecode
  • Plug in the Micro:bit to the computer
Click to expand

Code Walk Through:

Calculating the voltage from the analog output:

The voltage can be calculated from the sensor's analog output by mapping from the analog range 0  - 1023 to the millivolt range 0 - 3300. The code for this section will go inside the ‘forever’ block.

  • Retrieving the temperature sensors analog output: Select “analog read pin (pin number)” in the Pins tab in the Advanced section and change the pin number to P0
  • Mapping the analog Value: In the math tab choose “map (value) from low (value) high (value) to low (value) high (value) and change the values such that it maps the reading from pin 0 from 0 to 1023 and 0 to 3300; “map analog read pin P0 from low 0 high 1023 to low 0 high 3300”.
  • Creating a variable for the voltage: Select “Make a Variable” in the Variable tab and naming it “voltage”
  • Setting ‘voltage’ to the mapping calculation: Choose “set (variable name) to (value)” in the Variable tab, change variable name to voltage and place the “map analog read pin P0 from low 0 high 1023 to low 0 high 3300” block as the value 
Click to expand
Calculating the temperature:

We can use the fact that as the temperature increases, the voltage across the diode does as well at a known rate. The formula used is millivolts - 500 / 10. The code for this section will go inside the ‘forever’ block.

  • Creating a temperature variable: Select the “Make a Variable” in the Variable tab and naming it “temp”
  • To calculate the temperature :
    • In the Math tab choose the “(value) - (value)” block, and change the values such that the expression becomes “voltage - 500” where the voltage variable can be found in the Variables tab
    • Select the “(value) / (value)” block, and change the values such that the expression becomes voltage - 500 / 10 by placing the previous math expression inside this block
  • Setting the temperature variable: In the Variables tab choose the “set (variable name) to (value)”, change the variable name to temp and value to the formula code block
Click to expand
Displaying the temperature on the LED grid:

We can show the calculated temperature on the LED grid by pausing the code for a specified amount of time so that the micro:bit has enough time to display the temperature before executing the next action.The code for this section will go inside the ‘forever’ block.

  • Rounding the temperature to a few decimal places: In the Math tab, select “round 0” and place the variable temp (can be found in the Variables tab) inside the code snippet 
  • Displaying the temperature: In the basic tab select “show number”, and drag the “round temp” line inside the code
  • Pausing the code: Select “pause ms” in the Basic tab and setting it to 1000 (1 second)
Click to expand
Flashing the code onto the Micro:Bit:
  • Make sure the Micro:Bit is connected to the computer 
  • On the bottom left corner, click the “Download” button and follow the prompts

Python Code:

voltage = 0
temp = 0

def on_forever():
    global voltage, temp
    # Converting the analog reading to voltage & calculating the temperature
    voltage = Math.map(pins.analog_read_pin(AnalogPin.P0), 0, 1023, 0, 3300)
    temp = Math.idiv(voltage - 500, 10)
    # Displaying the temperature reading
    basic.show_number(Math.round(temp))
    basic.pause(10000)
basic.forever(on_forever)

Simulated Temperature Display:

Click to expand

Downloadable Content:

Please find this tutorial's python & hex file for microsoft makecode on our Github.

Credits:

  • Microsoft
  • The Micro:bit Community
  • The STEM Community
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