--- title: "A model drives a micro:bit" subtitle: "micro:bit and the computer · A model drives a build · Lesson 5" --- # A model drives a micro:bit **Name:** {{field-24}} **Date:** {{field-15}} **Class:** {{field-15}} > **Key question:** A sorting machine's camera and its motors are separate parts. The camera's model only says 'Plastic'; a small controller decides which flap to move. The two have to agree on every word. :::teacher-note **In one sentence:** Students send their model's labels from the board to a micro:bit over USB, program the micro:bit to act on each label and reply, then pass labels on by radio to a sorting flap. **Students should be able to say:** I can program a micro:bit to act on lines of text it receives over USB. I can explain why the sender and receiver must agree on every word. I can handle a label my program doesn't expect. **Width:** the unmarked parts are the floor every student does (predict, run, investigate and make). Typical adds the modify practice; wider adds the real-world contexts. They add contexts, not difficulty. Students work in the online tutorial alongside this sheet. ::: ## Predict ![The program as blocks](https://studio.learningwaypoints.com/tutorials/_pictures/makecode/code/9389c94224dd.png?v=dd2eb3a27a12856a) :::keep-together **Your model has a Neither class. The board sends "Neither" to a micro:bit running this program. What does it show?** ☐ Nothing ☐ An error ☐ P ☐ L My prediction, and why: {{lines-3}} ::: :::teacher-note **What happens:** L. The program checks only for "Paper"; else catches every other line, including "Neither". ::: ## Run Run the program in the tutorial. Was your prediction right? What was different? {{lines-2}} :::typical ## Run Run the program in the tutorial. Was your prediction right? What was different? {{lines-2}} ::: ## Investigate ![The program as blocks](https://studio.learningwaypoints.com/tutorials/_pictures/makecode/code/9389c94224dd.png?v=dd2eb3a27a12856a) :::keep-together ### What is sent **What travels down the USB cable when the board sends a label?** ☐ A number from 1 to 3 ☐ A line of text, such as Paper ☐ The whole model ☐ The photo ::: :::teacher-note **Answer:** A line of text, such as Paper Only the label, as text, ending with a new line. The micro:bit never sees the photo or the model. ::: :::keep-together ### Ben's sorter ![The program as blocks](https://studio.learningwaypoints.com/tutorials/_pictures/makecode/code/f4e32b2a3db4.png?v=afe8dce8bfa6f526) **Ben's model has classes Paper and Plastic. His micro:bit never shows anything. Why?** ☐ He checks for "paper" and "plastic", but the board sends "Paper" and "Plastic" ☐ Serial only works with numbers ☐ He needs a forever block ☐ His micro:bit is too slow ::: :::teacher-note **Answer:** He checks for "paper" and "plastic", but the board sends "Paper" and "Plastic" Text has to match exactly, capital letters included. Both sides must agree on every word. ::: :::keep-together ### Unsure labels **Why does the webcam wait for a label to hold for a moment above 80% before sending it?** ☐ The cable is slow ☐ So a model that flickers between two labels doesn't make the micro:bit jump back and forth ☐ The micro:bit can only read one label a minute ☐ So the model can retrain ::: :::teacher-note **Answer:** So a model that flickers between two labels doesn't make the micro:bit jump back and forth When the model is unsure, its top label changes many times a second. Acting on every change would make a sorter jitter. ::: :::typical ## Modify **Neither.** Give **Neither** its own branch that shows a cross, and make **Plastic** a branch of its own too. **Reply.** A sorter should say what it did. Make the micro:bit **reply** with **serial write value**: `bin` 1 for Paper, 2 for Plastic, 0 for anything else. On the board, the replies appear under the buttons. Work in the tutorial. Plan first: what will you change, and how will you test it? {{box-4}} :::teacher-note **One possible solution.** Other correct programs are fine; check that the program runs and does what the task asks. **Neither:** ![The program as blocks](https://studio.learningwaypoints.com/tutorials/_pictures/makecode/code/eab3070036f6.png?v=b95028ab128a52ac) **Reply:** ![The program as blocks](https://studio.learningwaypoints.com/tutorials/_pictures/makecode/code/5ea20258d9a6.png?v=7ade6b316a6f4267) ::: ::: :::typical ## Over radio A sorter on a conveyor belt is not plugged into a laptop. This is the **bridge** from **A radio bridge**: the micro:bit on the cable passes each line on by **radio**, and passes radio values back to the board. Add **on radio received string** so a second micro:bit shows the first letter of each label and replies **got 1**. Download the same program to both micro:bits; plug one into the computer. Work in the tutorial. Plan first: what will you change, and how will you test it? {{box-4}} :::teacher-note **One possible solution.** Other correct programs are fine; check that the program runs and does what the task asks. ![The program as blocks](https://studio.learningwaypoints.com/tutorials/_pictures/makecode/code/f80dea4ffd60.png?v=0a181b2992a09abd) ::: ::: ## Make a sorting flap Build a **sorting flap**: a servo on **P0** on the second micro:bit tips left for **Paper**, right for **Plastic**, and stays in the middle for anything else, then replies with the bin. Try it with your model and real items. Work in the tutorial. Plan first: what will you change, and how will you test it? {{box-4}} :::teacher-note **One possible solution.** Other correct programs are fine; check that the program runs and does what the task asks. ![The program as blocks](https://studio.learningwaypoints.com/tutorials/_pictures/makecode/code/558256353b3e.png?v=1bba60f61e3df43d) ::: :::wider ## On a real micro:bit - **Chrome or Edge only.** Safari, Firefox and iPads can't connect. - **"The micro:bit is busy"**: another tab (often MakeCode) is using the cable. Disconnect it there or close that tab. - **Same radio group** on both micro:bits, and a different group for every pair in the room. - A servo needs more power than USB sometimes gives: if it twitches or the micro:bit resets, use a battery pack or a servo board. ::: ## Exit ticket :::keep-together **The model sends "Glass", a class the micro:bit's program doesn't check for. What should the program do?** {{lines-3}} ::: :::teacher-note **Answer:** Something safe: an else branch that leaves the flap in the middle (or stops), so an unexpected label never causes a wrong action. :::