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µBOSS .... Test Instrumentation ... micro:bit

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Test Instrumentation

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This Project14 blog is about turning a BBC micro:bit into a test instrument. I call this a micro:bit of sense system or µBOSS.

The micro:bit already has a nice set of sensors but they aren't very easy to read on the built in LED display, so I thought I would display all the sensor readings on an LCD, turning it into a test instrument that has the following capabilities:

  • Thermometer
  • Volt Meter
  • Compass
  • Digital Level

Additional features include a lithium-polymer battery and a rectangular 3D printed case that allows flat surfaces to be measured for levelness.

The electronic design is based on a custom interconnect PCB that hosts a micro:bit connector, an LCD footprint, a power switch, a analog input connector and a charging connector.

The main parts look like this:

image

The micro:bit is programmed to display 6 sensed parameters on 6 lines of text.

Here is a video demonstrating the completed system:

 

The LCD really allows the micro:bit built-in sensors to be fully displayed.

I have been perfecting the the connection and programming of an LCD with a micro:bit and this project is a good way to demonstrate the potential of an LCD to enhance a micro:bit.

There is a deceptive amount of work involved in getting everything connected properly, programmed properly and fit properly in a slim package, but that also makes it more satisfying when it all works.

 

This short video shows the charging module in action:

 

made cool suggestion to use the LEDs as a bubble level - so here is single axis level with LEDs ....

 

 

This is the schematic for those that would like to make one of these for themselves:

 

image

 

Note there are 2 different pinouts for Nokia 5110 LCDs - I have an adapter card that allows either to be used, but the pinout should be checked if you are going to try this.

Here is the code to display all the sensors on the LCD:

 

from microbit import *
# Program to display BBC micro:bit sensor data on a Nokia 5110 LCD
# by Doug Wong
# 2018


spi.init(baudrate=1000000, bits=8, mode=0, sclk=pin13, mosi=pin15, miso=pin14) # setup for SPI communication with LCD
#lcdinit = [33, 184, 4, 20, 32, 12]  # HEX 21 B8 04 14 20 0C


pin8.write_digital(1)   # disable LCD
pin1.write_digital(0)  # reset LCD
pin1.write_digital(1)  # release reset pin
pin8.write_digital(0)   # enable LCD
pin2.write_digital(0)  # select command mode
spi.write(b'\x21\xb8\x04\x14\x20\x0c')  #LCD init
pin2.write_digital(1)  # select data mode


display.scroll ("BOSS")  #splash screen


def lcd(kb):            # funtion to convert ascii characters to 56 pixel LCD representations and display
                        # each character is made up of 7 bytes where each byte is 8 vertical pixels
    if kb >= " ":
            if kb < "[":
                if kb < "!":
                    spi.write(b'\x00\x00\x00\x00\x00\x00\x00')  #space
    if kb > " ":
        if kb < "[":
            if kb < "#":
                spi.write(b'\x00\x00\x00\xbe\x00\x00\x00')  #!
            elif kb < "$":
                spi.write(b'\x00\x48\xfe\x48\xfe\x48\x00')  ##
            elif kb < "%":
                spi.write(b'\x00\x048\x54\xfe\x54\x24\x00')  #$
            elif kb < "&":
                spi.write(b'\x00\x46\x26\x10\xc8\xc4\x00')  #%
            elif kb < "'":
                spi.write(b'\x00\x6c\x92\xaa\x44\xc0\x00')  #&
            elif kb < ")":
                spi.write(b'\x00\x00\x38\x44\x82\x00\x00')  #(
            elif kb < "*":
                spi.write(b'\x00\x00\x82\x44\x38\x00\x00')  #)
            elif kb < "+":
                spi.write(b'\x00\x28\x10\x2c\x10\x28\x00')  #*
            elif kb < "-":
                spi.write(b'\x00\x00\xa0\x60\x00\x00\x00')  #,
            elif kb < ".":
                spi.write(b'\x00\x10\x10\x10\x10\x00\x00')  #-
            elif kb < "/":
                spi.write(b'\x00\x00\x60\x60\x00\x00\x00')  #.
            elif kb < "1":
                spi.write(b'\x00\x78\xa2\x92\x8a\x74\x00')  #0
            elif kb < "2":
                spi.write(b'\x00\x00\x84\xfe\x80\x00\x00')  #1
            elif kb < "3":
                spi.write(b'\x00\x44\xc2\xa0\x92\x8c\x00')  #2
            elif kb < "4":
                spi.write(b'\x00\x44\x82\x92\x92\x6e\x00')  #3
            elif kb < "5":
                spi.write(b'\x00\x30\x28\x24\xfe\x20\x00')  #4
            elif kb < "6":
                spi.write(b'\x00\x4e\x8a\x8a\x8a\x70\x00')  #5
            elif kb < "7":
                spi.write(b'\x00\x78\x94\x92\x92\x40\x00')  #6
            elif kb < "8":
                spi.write(b'\x00\x02\xc2\x12\x0a\x06\x00')  #7
            elif kb < "9":
                spi.write(b'\x00\x6c\x92\x92\x92\x6c\x00')  #8
            elif kb < ":":
                spi.write(b'\x00\x0c\x92\x92\x52\x3c\x00')  #9
            elif kb < ";":
                spi.write(b'\x00\x00\x6c\x6c\x00\x00\x00')  #:
            elif kb < "@":
                spi.write(b'\x00\x04\x02\xa2\x12\x0c\x00')  #?
            elif kb < "A":
                spi.write(b'\x00\x44\xa2\xc2\x82\x7c\x00')  #@
            elif kb < "B":
                spi.write(b'\x00\xfc\x12\x12\x12\xfc\x00')  #A
            elif kb < "C":
                spi.write(b'\x00\xfe\x92\x92\x92\x6c\x00')  #B
            elif kb < "D":
                spi.write(b'\x00\x7c\x82\x82\x82\x44\x00')  #C
            elif kb < "E":
                spi.write(b'\x00\xfe\x82\x82\x82\x7c\x00')  #D
            elif kb < "F":
                spi.write(b'\x00\xfe\x92\x92\x92\x82\x00')  #E
            elif kb < "G":
                spi.write(b'\x00\xfe\x12\x12\x12\x02\x00')  #F
            elif kb < "H":
                spi.write(b'\x00\x7c\x82\x82\xa2\x64\x00')  #G
            elif kb < "I":
                spi.write(b'\x00\xfe\x10\x10\x10\xfe\x00')  #H
            elif kb < "J":
                spi.write(b'\x00\x00\x82\xfe\x82\x00\x00')  #I
            elif kb < "K":
                spi.write(b'\x00\xe0\x82\x82\xfe\x02\x00')  #J
            elif kb < "L":
                spi.write(b'\x00\xfe\x10\x28\x44\x82\x00')  #K
            elif kb < "M":
                spi.write(b'\x00\xfe\x80\x80\x80\x80\x00')  #L
            elif kb < "N":
                spi.write(b'\x00\xfe\x02\x3c\x02\xfe\x00')  #M
            elif kb < "O":
                spi.write(b'\x00\xfe\x04\x38\x40\xfe\x00')  #N
            elif kb < "P":
                spi.write(b'\x00\x7c\x82\x82\x82\x7c\x00')  #O
            elif kb < "Q":
                spi.write(b'\x00\xfe\x22\x22\x22\x1c\x00')  #P
            elif kb < "R":
                spi.write(b'\x00\x7c\x82\xa2\x42\x7c\x00')  #Q
            elif kb < "S":
                spi.write(b'\x00\xfc\x22\x22\x52\x8c\x00')  #R
            elif kb < "T":
                spi.write(b'\x00\x4c\x92\x92\x92\x64\x00')  #S
            elif kb < "U":
                spi.write(b'\x00\x02\x02\xfe\x02\x02\x00')  #T
            elif kb < "V":
                spi.write(b'\x00\x7e\x80\x80\x80\x7e\x00')  #U
            elif kb < "W":
                spi.write(b'\x00\x3e\x40\x80\x40\x3e\x00')  #V
            elif kb < "X":
                spi.write(b'\x00\x7e\x80\x70\x80\x7e\x00')  #W
            elif kb < "Y":
                spi.write(b'\x00\xc6\x28\x10\x28\xc6\x00')  #X
            elif kb < "Z":
                spi.write(b'\x00\x06\x08\xf0\x08\x06\x00')  #Y
            elif kb < "[":
                spi.write(b'\x00\xc2\xa2\x92\x8a\x86\x00')  #Z
            elif kb < "_":
                spi.write(b'\x00\x10\x08\x04\x08\x10\x00')  #^
            else:
                spi.write(b'\x00\x00\x00\x00\x00\x00\x00')  #.


def dl():                                                   # funtion to display a line
    for i in range(0, 12):                                  # loop through 1 line of characters
        c = l[i]                                            # get next character in the line
        lcd(c)                                              # display the character
    
while True:
    
    l = "TEMP : " + str(temperature() - 4) + "           "          # compose temperature line
    dl()                                                            # display line of text
    l = "VOLT : " + str(pin0.read_analog() * .0031) + "           " # compose voltage line
    dl()                                                            # display line of text
    l = "HEAD : " + str(compass.heading()) + "            "         # compose compass heading line
    dl()                                                            # display line of text
    l = "X ACC: " + str(accelerometer.get_x()) + "           "      # compose X acceleration line
    dl()                                                            # display line of text
    l = "Y ACC: " + str(accelerometer.get_y()) + "           "      # compose Y acceleration line
    dl()                                                            # display line of text
    l = "Z ACC: " + str(accelerometer.get_z()) + "           "      # compose Z acceleration line
    dl()                                                            # display line of text


    sleep(350)                                                  # wait 350 ms before displaying another set of readings

 

 

Relevant Links:

Test Instrumentation

Project14 | Test Instrumentation: Tool Kit Prizes: micro:bits for Testing Tool: bits!

 

This project won some loot from element14 which is shown here:

Parents

  • I loved this project! First because of the use of the SPI protocol while I already have difficulties (it will be great if you share the software. I tried to manage SPI on micro:bit on both microPython and Javascript with no success. I am sure that something is wrong in the code but I can't figure out what it is.

     

    What I appreciated a lot is the use of the LCD screen and the LED grid of the micro:bit in conjunction. About leveling I have recently done some thoughts. What is the use of a level measurement in an instrument that can't be precise in terms of absolute? This thought is not related to your project, it's a general consideration. To put the hand on the problem I bought a Chinese digital level I will show you in the image below.

     

    image

    Despite how much tool is precise, the metallic part is surely trustable respect the physical level indicators (the traditional ones) while the Chinese plastic insertion with the display and the electronic circuit it is very improbable that it is inserted perfectly aligned respect the other parts. We can expect this kind of precision on more and more expensive devices, not with this 5 Euro tool.

    Ok, so why a digital inclinometer? I played a while and I discovered the trick. There is the reset button!

    So, I put over a plane (or not a plane, just a surface). Then I RESET and the digital value goes to zero. At this point - for example - I can position another part in a very precise way exactly in the position I want. This makes extremely useful and easier to place two objects at a specific degree despite their real orientation. Maybe the worth to use one of the two micro:bit buttons to include a similar behavior?

     

    Enrico

  • in reply to balearicdynamics

    They are very handy tools : ) I have a low-cost one too (different to this one), and although it is not long, it is good enough to be approximately sure before pulling out the larger level (and sometimes the short length is handy when rotating, to ensure it is level in two dimensions. Sometimes I trust eyeball'ed measurements more : ) but then the level indicator provides confidence if my judgement was good or not : )

    There is a very fancy electronic one that looks like a drawing compass, for creating angles.. but it is quite expensive (the more expensive version unlocks higher accuracy in the software I think).

    I've seen crazy DIY people over-trusting their old bubble levels and not stepping back and eyeballing for confidence, and not noticing that it is not precisely on position (since some bubble levels are rotatable!) yet visually it is clear.. : )

    Also, maybe the measurement is fine in your photo and the Apple Macbook is 1.4 degrees too bent : )

  • in reply to shabaz

    I always rotate the spirit level through 180degrees before using it. If you get two different readings then the bubble vial isn't true to the edge.

     

    Ironically the last time I found one that was very badly out, was on a training course for the safe use of PASMA scaffold towers...

  • in reply to beacon_dave

    Hi Dave,

    This is a simple and effective technique that I had to learn the hard way. I was a technician with a mission trip to Nicaragua where I had the job of mounting a dental x-ray machine to a concrete wall.  The dental x-ray unit must be mounted level in the two vertical planes or the arm will drift. Mounting to concrete is also a challenge as the drills like to walk but that is another issue. In this case the tools were supplied and I proceeded to mount the x-ray using the spirit level supplied. On completion the arm drifted and a good eye ball of the unit also indicated it was not level. It turned out that if I had applied your test prior to use I would have seen the approximate 5 degrees the level was off. Lesson learned as I now routinely flip the level to confirm level is level in both directions.

    John

Comment
  • in reply to beacon_dave

    Hi Dave,

    This is a simple and effective technique that I had to learn the hard way. I was a technician with a mission trip to Nicaragua where I had the job of mounting a dental x-ray machine to a concrete wall.  The dental x-ray unit must be mounted level in the two vertical planes or the arm will drift. Mounting to concrete is also a challenge as the drills like to walk but that is another issue. In this case the tools were supplied and I proceeded to mount the x-ray using the spirit level supplied. On completion the arm drifted and a good eye ball of the unit also indicated it was not level. It turned out that if I had applied your test prior to use I would have seen the approximate 5 degrees the level was off. Lesson learned as I now routinely flip the level to confirm level is level in both directions.

    John

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