PJ015: The Sound Level Bar Meter

This project makes a fun sound level bar meter by using the LED screen on Micro:bit, it monitors the environment sound, indicates the sound level by showing 0-5 levels, the challenge part makes it more interesting by turning it into a dynamic noise alarm, using adaptive max level in real time. Goals:

Array/list concept and basic usage
Learn using "images array" to make simple animations as a useful visualization of data level
Concept and practice of "data scaling and mapping"

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Result Demo

This is the demo for the basic functions. Please go to the Challenge chapter for the demo of challenging result.

PJ015_The_Sound_Level_Bar.mp4

Task 1: Monitor Environment Sound Level

Task 2: Make a List of Images, Show a Specific Image by Button A/B

Task 3: Scale "Sound Level" Values to Map Valid Index of Array

Challenge 1: Make it More Sensitive

Challenge 2: Adaptive Noise Alarm

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 starts monitoring the environment sound level continuously, and show the level bar on LED screen, indicating how much level of the sound, the monitoring and visualization is almost real time, should not have obvious delay or mismatching.

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

Task 1: Monitor Environment Sound Level

Get Sound Level

The result of this block is a number between 0 (low sound) and 255 (loud sound) which tells how loud the sounds are that the microphone hears.

Input ->

Use "Serial Write" to Collect Data

Use "Serial Write" to visualize the real time changing of sound level.

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

Solution 1

Solution 2: Use "Loops" block

How Big Value Do you Catch?

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

Try to shout, how big value can you catch?

Task 2: Make a List of Images, Show a Specific Image by Button A/B

Create a List of Images

Use this to quickly create an array with the default name as "list", put this to "on start".

Then fill in the array using "create image", add more elements of array by clicking the "+" icon.

Arrays ->

Images ->

Click "+" to add more elements

When >3, it becomes vertical

The array of 5 images

Pick An Image from the Array

The array has index starting from 0, use the valid index to find the element of the array, please be careful to keep the index as valid! Don't go "out of range".

Arrays ->

Show a Specific Image from the Array

Use this to "show image", you need to fill in an "image", but not the array!

Images ->

What do You Find?

It's smart to create a variable "index", and temporarily, we use button A/B to change the "index" value for testing this task. And it's good to add "index" to "serial write" for debugging.

What do you find? What happens if "index" goes "out of range"?

Task 3: Scale "Sound Level" Values to Map Valid Index of Array

The Last Step

This is the last step of this project, we want to set the index according to the sound levels. Basically, this is what it looks like, for junior students, it's OK to just copy this implementation and make it work.

Optional: Dynamically Get Array Length

The images array could be changed in its size, it's smart and more professional to do like this:

Optional: Dig How it Works

How does it work? Think and discuss, it's challenging, but not so hard to understand the basic logic.

Challenge 1: Make it More Sensitive

As you might see, although in theory, the max value of "sound level" is 255, but even if we shout loud, it's very hard to see higher values than 200.

If we always map from "low 0 high 255", it makes the bar leveling jumping not so actively, how can we make it more "sensitive"?

The "high" Value Matters

Try out a smaller "high" value, download and test

What differs in actual?
Any "out of range" risks?

Challenge 2: Adaptive Noise Alarm

Based on the basic requirement, let's make the sound sensitivity more intesting and useful

Add adaptive max_sound_level, we will expand the "high" end of mapping to be a new "max" level of sound that we listen from the environment after 10 times of continuous hitting the old "max"
Press "Logo" to reset the max_sound_level, i.e. we reset the sound sensitivity

Below are some hints to make it happen, but not in every detail, and not as step by step, you need to figure out the full working program.

PJ015_The_Sound_Level_Bar_Meter_Challenge_Adaptive_Noise_Alarm.mp4

Hint: New Variable to Share "Sound Level" in Sync

In this challenge, the sound_level is referred multiple times, and there is parallel handling of this value, it's risky to capture the sound level again and again in different places, because whenever you read the sound level, it's always the latest

It could bring "sync" problem for parallel threads
It stresses the system by unnecessary extra reading from sensor
It makes confusing logic in the programming

Hint: New Variables to Remember "Max" Level and "Hitting Count"

We need to remember the last max level, so to judge if current sound level is bigger, so to update the new "high" value in mapping.

It makes better sense to update the max_level only after some amount of tolerance, but not change it immediately, to reduce interference from strange sudden noise.

Hint: The Main Logic to Update "Max" Level

The main logic is

If "sound_level > max_level" and "hitting_count" reaches a threshold, say 10, then we update the "max_level"

It's smart to add some debugging information by "serial write"

Click to find the copy if you need

Think Again: "Constrain"

If you are careful, there is a new "constrain" used before "map", why? What happens if we don't add this?

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.

Referred/Used By

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