PJ016: The Digital Level Ruler

This project makes a useful leveler (spirit level ruler) by using the built-in accelerometer and LED screen on Micro:bit, it monitors the roll/pitch from accelerometer sensor, and visualize the leveling status by the moving dot on the LED screen. The challenge part adds dynamic warning sound for how much the levelling is reached, making the project more fun and practically useful. Goals:

Get to know roll/pitch concept, and accelerometer sensor
Coordinate of the LED matrix on Micro:bit
Concept and practice of "data scaling and mapping"

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Result Demo

Here is the demo of the basic requirement, please go to the Challenge chapter for the demo of challenging result.

PJ016_The_Digital_Level_Ruler.mp4

Knowledge Preparations

The LED Matrix of Micro:bit

Task 1: Monitor Roll/Pitch Angles From Accelerometer Sensor

Task 2: Map Roll/Pitch Angles to LED Coordinates X/Y

Challenge: Dynamic Warning Sound for Levelling

Challenge: Blink for Levelling

Discussion & Sharing

The Working Copy

Referred/Used By

Requirement

Hardware setup

This project uses 1 Micro:bit board with a USB cable, nothing else needed.

Programming

When powering up, the Micro:bit shows a dot on the LED screen, this dot indicates the level status, if the level is status is good, then the dot moves to the middle, otherwise, the dot moves to the direction that the level is lower.

Effort Estimation

[ ] Simple: 30-60 minutes

[x] Moderate: 1-2 hours

[ ] Challenging: more than 2 hours

The estimation bases on average situation without unexpected troubleshooting, assuming that the student meets prerequisites. It only indicates rough time needed to complete this project, but not about technical difficulty, not covering discussion and sharing time. Here is a possible breakdown:

5 minutes: Understand requirement and solution, collect materials
10-15 minutes: Task 1: Monitor Environment Sound Level
10-15 minutes: Task 2: Make a List of Images, Show a Specific Image by Button A/B
30-45 minutes: Task 3: Scale "Sound Level" Values to Map Valid Index of Array

The challenge topic is not included in effort estimation, it could take extra 45-60 minutes for that part.

Prerequisite

One should have prior knowledge

Micro:bit V2 board: Know what they are, better to have prior experience with it
MakeCode by Microsoft, the programming tool, better to have prior experience using it with Micro:bit

Tools & Materials

A laoptop or tablet with internet access
1x Micro:bit V2 board , with USB cable

Knowledge Preparations

Roll & Pitch Angles

Aircraft principal axes (wikipedia)

Yaw

Pitch

Roll

Accelerometer

IMU (Inertial Measurement Unit, wikipedia)

Accelerometer (wikipedia)
Gyroscope
Magnetometers

The LED Matrix of Micro:bit

Micro:bit LED screen has 25 LED arranged in a 5x5 grid.
Use (x,y) coordinates to specify a particular LED, x is the horizontal position (0,1,2,3,4) y is the vertical position (0, 1, 2, 3, 4).
Use plot and unplot to turn a LED on or off, or toggle to flip the state.
More info here from MakeCode document (link)

Task 1: Monitor Roll/Pitch Angles From Accelerometer Sensor

Capture Roll/Pitch Level

Similar as "Sound Level", there are ready-made blocks to capture the roll/pitch level, the input is already converted from analog to digital values, ranged -180~180 degrees.

Use "Serial Write" to Collect Data

Use "Serial Write" to visualize the real time changing of roll/pitch input.

Adding a small delay helps slowing down a little bit of the data, so to observe clearer.

Test and Analyze

After "Downloading", click "Show data Device" to visualize the real time data.

Which direction makes changes of roll or pitch input?
Which exact way makes "-" or "+" values
Can you find out the boundary -180 or 180 positions?
Considering the final product we want to build, which angle range is the most interesting to catch?

Task 2: Map Roll/Pitch Angles to LED Coordinates X/Y

Prototype: Does it Work Well?

Tips:

Remember to "unplot" before "plot", otherwise, "ghost trailing" bug happens
Remember to "round" the "map", so to get "whole number" for LED coordinate

Find out how it works in actual testing, how should we improve it?

Here is a prototype

Input Range of Mapping Matters

As you have seen, using the full "-180~180" range as input for mapping make it not practically useful, the sensitivity is very dull.

Tips: The low/high ends of the input range matters, try to narrow them, test and find out

Does this work well? Why?

"Out-of-Range" Mapping?

Does this work well? Why?

Constrain the Input for Mapping

Constrain the input data (i.e. roll, pitch) to be a valid range to be mapped!

Finally...

Here is a final working copy, if you need

Challenge: Dynamic Warning Sound for Levelling

Requirements & Demo

Add a warning sound tipping how much we have reached the right levelling (middle dot)
Sound differently when reaching more and more levelled
- It beeps more and more urgently (faster beeping) when the dot goes further away from the middle dot
- It beeps less and less urgently (slower beeping) when the dot does closer and closer to the middle dot
- It stops beeping when it finally reaches the middle dot
Enable/disable the beeping sound by pressing "Logo" button

PJ016_The_Digital_Level_Ruler_Challenge_Demo.mp4

Calculate the Deviation

The perfect middle dot is (2, 2).

When we say "going away from this middle dot", it could mean the delta of x-difference or y-difference.

A reasonable algorithm to count the deviation should consider both directions difference. i.e.

x diff + y diff

Beep in Difference "Speed"

Beat is the time duration in milliseconds, by changing the beat for play-rest looping, it creates a beeping speeding.

It's similar as PJ014: The Blinking Dot solution for blinking the LED.

The Prototype

This prototype looks more or less correct for the main need. Try it out and think about the remaining things to fix:

When reaching the middle dot (2.2), we want it to stop beeping, how to do this? Remember the "0Hz" issue in PJ014?
We need also an extra switch to enable/disable the warning sound by pressing "Logo"

Finally...

Here is a final working copy, if you need

Challenge: Blink for Levelling

Blink for Levelling

Make the dot blinking, and let it

blink faster when getting less levelled
blink slower when becoming more levelled
make it constant on (no blinking) when reaching right levelled (middle dot)

We don't provide any tips and hints for this part, please explore and try things out.

Discussion & Sharing

This optional part covers further competence development, in terms of testing, troubleshooting, analysis, documentation, flow chart diagrams practices, etc.

Presentation & Demo

Stand in front of the class, share with your group what you have made, please cover important points

Tell what it is your product
Demonstrate how it works
Explain how it works

Troubleshooting Stories

Share with your group about

What troubles you met
How you analyze
How you get help
How you solve it
What you have learnt

The Working Copy

Find out working copy as a MakeCode shared project.

PJ016: The Digital Level Ruler

Referred/Used By

Used by LP2438: Data Scaling/Mapping and Visualization, 24w38

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