Broadcast Flow¶

Run the Broadcast Flow MicroSim Fullscreen
Edit in the p5.js Editor

About This MicroSim¶

This MicroSim visualizes how Scratch's broadcast and "when I receive" blocks let sprites communicate with each other. Selecting one of five sample messages (such as game-start or player-hit) shows which sprite sends it and which sprites receive it, and an animated pulse traces the message traveling from sender to receivers.

How to Use¶

Click one of the five broadcast-name buttons (game-start, player-hit, coin-collected, level-complete, game-over) to select a message; its sender, receivers, and sync/async status appear in the info panel.
Click "Trigger Broadcast" to animate the message moving from the sending sprite to its receivers.
Check "Show 'and wait' sync" to replay the broadcast continuously as a synchronous (broadcast and wait) call.
Check "Show code snippets" to show or hide the matching "when I receive" code example in the info panel.

Iframe Embed Code¶

You can add this MicroSim to any web page by adding this to your HTML:

<iframe src="https://dmccreary.github.io/scratch-textbook/sims/broadcast-flow/main.html"
        height="545px"
        width="100%"
        scrolling="no"></iframe>

Lesson Plan¶

Grade Level¶

Grades 4-6 (ages 9-12)

Duration¶

15-20 minutes

Prerequisites¶

Understands events and hat blocks (for example, "when green flag clicked") and has built at least one script that starts with a hat block.
Knows what a sprite is and that a Scratch project can have several sprites on the stage at once.
Has been introduced to the broadcast and when I receive blocks (see the Broadcast Messages section earlier in this chapter) before using this MicroSim to see them animated.

Activities¶

Exploration (5 min): Students click through each of the 5 broadcast messages (game-start, player-hit, coin-collected, level-complete, game-over) and read which sprite sends it and which sprites receive it in the info panel.
Guided Practice (7 min): Students click "Trigger Broadcast" to watch the pulse travel from sender to receivers, then check "Show code snippets" to match the animation to the actual broadcast and when I receive blocks, discussing why every receiving sprite can react to the same message differently.
Assessment (5 min): Students check "Show 'and wait' sync" and explain, in their own words, the difference between a plain broadcast and a broadcast ... and wait — specifically, what the sending sprite does while it waits.

Assessment¶

Student can explain that one broadcast message can be received by multiple sprites at once, can identify which sprite is the sender versus the receivers for a chosen message, and can describe the difference between broadcast and broadcast and wait.