--- title: "Wait for a press" subtitle: "micro:bit Foundations · Show and react · Lesson 3" --- # Wait for a press **Name:** {{field-24}} **Date:** {{field-15}} **Class:** {{field-15}} > **Key question:** A doorbell, a game controller, a TV remote: each one waits for a press, then does one job. :::teacher-note **In one sentence:** Students make programs that wait for a button press or a shake, and see that an event block runs its blocks every time its event happens, and only then. **Students should be able to say:** I can make the micro:bit react when a button is pressed or it is shaken. I can say when on start, forever and an event block each run. I can add a new event block to react to something new. **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 There are three groups of blocks here. Which ones run straight away, and which ones wait? ![The program as blocks](https://studio.learningwaypoints.com/tutorials/_pictures/makecode/code/ae562876db2f.png?v=1b0dee3e7ad62b74) :::keep-together **What does the micro:bit show when it starts, and then after you press B?** ☐ Asleep, then sad when B is pressed ☐ Nothing until a button is pressed ☐ Happy, then sad, straight away when it starts ☐ Asleep, then happy and sad together My prediction, and why: {{lines-3}} ::: :::teacher-note **What happens:** It shows the asleep face at the start, then waits. Pressing B runs only the blocks inside 'on button B pressed', so the sad face shows. ::: ## Run Run the program in the tutorial. Was your prediction right? What was different? {{lines-2}} ## Investigate This program has four groups of blocks. Try it in your head first. ![The program as blocks](https://studio.learningwaypoints.com/tutorials/_pictures/makecode/code/8959e874587e.png?v=7da8165414186f1a) :::keep-together ### When does it run? **Match each block with when its blocks run.** A. again and again, by itself B. each time the micro:bit is shaken C. each time A is pressed D. once, when the micro:bit switches on {{columns 60% 40%}} {{rows 1}} | Part | Letter | |---|---| | `on start` | | | `forever` | | | `on button A pressed` | | | `on shake` | | ::: :::teacher-note **Answer:** on start → D. once, when the micro:bit switches on; forever → A. again and again, by itself; on button A pressed → C. each time A is pressed; on shake → B. each time the micro:bit is shaken ::: :::keep-together ### Count the presses **You press A four times. How many times does the happy face appear?** Answer: {{field-15}} ::: :::teacher-note **Answer:** 4 The blocks inside 'on button A pressed' run once for every press. ::: :::keep-together ### Ben's button Ben's program used an **if** block from Logic. Read this for now: it asks a yes-or-no question, *is A pressed right now?*, and runs the blocks inside only if the answer is yes. You will use **if** properly in a later lesson. ![The program as blocks](https://studio.learningwaypoints.com/tutorials/_pictures/makecode/code/5f19ab5c2fb6.png?v=3de5bf0f36b8d7bf) **Ben wants A to show a heart. He put this in on start. He presses A and nothing happens. Why?** ☐ He needs a pause first ☐ on start checks the button once, when the micro:bit switches on, before he presses it ☐ Hearts only work in forever ☐ A is broken in the simulator ::: :::teacher-note **Answer:** on start checks the button once, when the micro:bit switches on, before he presses it on start runs once, at the very start. By the time Ben presses A, the check is long over. 'on button A pressed' waits for the press instead. ::: :::typical ## Modify **Change the faces.** Choose different pictures for **A** and **B**. **Press both.** Add a third event block for **A+B** (both buttons at once). Make it show a picture of your choice. 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. **Press both:** ![The program as blocks](https://studio.learningwaypoints.com/tutorials/_pictures/makecode/code/aabaf56f0de0.png?v=a4453021090bb907) ::: ::: ## Mix it up Read the animation from the top, the way forever goes round it. ![The program as blocks](https://studio.learningwaypoints.com/tutorials/_pictures/makecode/code/00b21d278056.png?v=618b2949268e53db) :::keep-together **This animation runs in forever. Which picture stays on the longest each time round?** ☐ The heart ☐ They all stay the same time ☐ The small heart ☐ The tick ::: :::teacher-note **Answer:** The tick Each pause holds the picture just before it. The tick is followed by pause 1000, the longest pause, so it stays longest. ::: ## Make Build a **signal board** for a bike rider: - **A** shows an arrow pointing left. - **B** shows an arrow pointing right. - **A+B** shows a cross for "stop". - **Shake** shows a surprised face. 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/fe54dba193c9.png?v=e5a418c982555710) ::: :::wider ## Change a bike indicator Real bike indicators flash. This one flashes each arrow twice. Make it flash three times, then make **A+B** flash a warning (both arrows, or a picture you draw). Work in the tutorial. Plan first: what will you change, and how will you test it? {{box-4}} ::: ## Exit ticket :::keep-together **Why does 'if button A is pressed' in on start not work, when 'on button A pressed' does?** {{lines-3}} ::: :::teacher-note **Answer:** on start checks once, when the micro:bit switches on, before anyone presses. The event block waits and runs every time A is pressed. :::