--- title: "Commands from the computer" subtitle: "micro:bit and the computer · Talk over USB · Lesson 2" --- # Commands from the computer **Name:** {{field-24}} **Date:** {{field-15}} **Class:** {{field-15}} > **Key question:** A 3D printer, a laser cutter and a robot arm in a factory all take orders from a computer as short lines of text: move here, heat up, stop. The machine's own program decides what each line means. :::teacher-note **In one sentence:** Students program a micro:bit to act on words the computer sends over USB, reply to each one, and handle words it doesn't know. **Students should be able to say:** I can make a micro:bit act on a line of text sent from the computer. I can explain why the words must match exactly. I can reply to each command, including words my program doesn't know. **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/a2d1ac736d04.png?v=fa4f2bf6375a7178) :::keep-together **The computer sends the line Happy (with a capital H) to a micro:bit running this program. What does it show?** ☐ A happy face ☐ The word Happy ☐ A sad face ☐ Nothing My prediction, and why: {{lines-3}} ::: :::teacher-note **What happens:** Nothing. The program checks for happy with a small h. Text must match exactly, so Happy matches neither branch. ::: ## 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/a2d1ac736d04.png?v=fa4f2bf6375a7178) :::keep-together ### When it runs **When does on serial data received run?** ☐ Each time a whole line arrives (it ends with a new line) ☐ When a button on the micro:bit is pressed ☐ Every half second ☐ Only when the micro:bit starts ::: :::teacher-note **Answer:** Each time a whole line arrives (it ends with a new line) It waits for the end of a line, then runs once. read line gives you that line, without its new line. ::: :::keep-together ### Ben's micro:bit ![The program as blocks](https://studio.learningwaypoints.com/tutorials/_pictures/makecode/code/806696a7939d.png?v=586802d837e622ff) **Ben's micro:bit never reacts, whatever the board sends. His program starts with on serial data received with delimiters comma. Why?** ☐ He needs a forever block ☐ The cable is too slow ☐ It waits for a comma, but the board ends each line with a new line, so it never runs ☐ Commas are not allowed in serial ::: :::teacher-note **Answer:** It waits for a comma, but the board ends each line with a new line, so it never runs The delimiter is the character that ends a message. The board ends each line with a new line, so the micro:bit must wait for a new line. ::: :::keep-together ### Replies **Why is it useful for the micro:bit to send a reply, such as ok?** ☐ Replies are needed for the LEDs to work ☐ Replies make the cable faster ☐ The micro:bit forgets the command otherwise ☐ The computer then knows the command arrived and was understood ::: :::teacher-note **Answer:** The computer then knows the command arrived and was understood Without a reply the sender can't tell whether a command arrived, or whether it was a word the micro:bit doesn't know. ::: :::typical ## Modify **A new command.** Add a **heart** command. On the board, type **heart** in the box to test it. **Reply.** Make the micro:bit **reply**: **ok** when it knows the word, **?** when it doesn't. The board shows the replies. 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. **A new command:** ![The program as blocks](https://studio.learningwaypoints.com/tutorials/_pictures/makecode/code/ec79aaf7cfd6.png?v=8e3d7f3dcd65564d) **Reply:** ![The program as blocks](https://studio.learningwaypoints.com/tutorials/_pictures/makecode/code/08fd679918b7.png?v=805a158479c23eae) ::: ::: ## Make Make a **desk lamp** the computer controls. **on** lights every LED, **off** clears the screen, **count** shows (and sends back) how many commands it has had. Reply **ok** to on and off and **?** to anything else. 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/01eb0b88e5c6.png?v=4fed34d5f34d5eb2) ::: :::typical ## Test the lamp Download your lamp to a micro:bit, connect it, and use the buttons. Type a word it doesn't know, too. ::: ## Exit ticket :::keep-together **The computer sends Stop but the micro:bit's program checks for stop. What happens, and how would you fix it?** {{lines-3}} ::: :::teacher-note **Answer:** Nothing matches, so nothing happens (or the else runs). Make both sides use exactly the same word. :::