Add micro:bit distance checker answer key (social distancing project)

content/english/microbit-distance-checker/answer-key.md

@@ -0,0 +1,160 @@
+---
+title: "micro:bit distance checker - Answer key"
+date: 2024-07-29T00:00:00-07:00
+draft: false
+weight: 15
+hidden: true
+---
+
+{{% notice note %}}
+This is a teacher reference for the micro:bit Wireless Social Distancing workshop. The workshop walks students through building a complete project step by step using MakeCode Blocks. This answer key provides the final complete code (in both Blocks description and JavaScript), explains the key concepts, and includes troubleshooting guidance.
+{{% /notice %}}
+
+## Complete solution
+
+### Final code (JavaScript equivalent)
+
+This is the complete program that students build across all workshop activities:
+
+```javascript
+radio.onReceivedNumber(function (receivedNumber) {
+    strength = radio.receivedPacket(RadioPacketProperty.SignalStrength)
+    if (strength > -67) {
+        basic.showIcon(IconNames.Sad)
+    } else {
+        basic.showIcon(IconNames.Happy)
+    }
+})
+let strength = 0
+radio.setGroup(1)
+basic.forever(function () {
+    radio.sendNumber(0)
+})
+```
+
+### Final code (Blocks description)
+
+For teachers who prefer to follow along with the block-based view:
+
+| Block location | Block | Settings |
+|---------------|-------|----------|
+| **on start** | `radio set group` | Group: `1` |
+| **forever** | `radio send number` | Number: `0` |
+| **on radio received (receivedNumber)** | `set strength to` | `received packet signal strength` |
+| (inside received block) | `if strength > -67 then` | Show icon: sad face |
+| (else) | `else` | Show icon: happy face |
+
+**What it does:** Each micro:bit continuously broadcasts a radio signal. When it receives a signal from another micro:bit, it checks the signal strength. If the signal is stronger than -67 dBm (meaning the micro:bits are less than 6 feet / 2 meters apart), it shows a sad face. If the signal is weaker (meaning they are far enough apart), it shows a happy face.
+
+## Step-by-step breakdown
+
+### Step 1: What is a micro:bit (page 1)
+
+This is an introductory page. No code is written. Key points:
+
+- micro:bit features: 25 LEDs, 2 buttons, IO pins, compass, accelerometer, Bluetooth
+- Students unpack their hardware: micro:bit, 2 batteries, USB cable, battery holder
+- **Simulator:** Students without hardware can use the MakeCode simulator with two virtual micro:bits side by side. The radio antenna (yellow square wave) can be clicked and dragged to simulate signal strength changes.
+- Signal strength threshold for the simulator: `strength > -67` triggers the sad face
+
+### Step 2: Broadcasting a signal (page 2)
+
+**Code added in this step:**
+
+```javascript
+// on start
+radio.setGroup(1)
+
+// forever
+basic.forever(function () {
+    radio.sendNumber(0)
+})
+```
+
+**Key concepts:**
+- `radio set group 1` goes in the "on start" block so it runs once when the micro:bit powers on
+- All micro:bits must use the same group number to communicate
+- `radio send number 0` goes in the "forever" block to continuously broadcast
+- The actual number sent (0) does not matter for this project; we only care about signal strength
+
+### Step 3: Receiving a message (page 3)
+
+**Code added in this step:**
+
+```javascript
+radio.onReceivedNumber(function (receivedNumber) {
+    strength = radio.receivedPacket(RadioPacketProperty.SignalStrength)
+})
+let strength = 0
+```
+
+**Key concepts:**
+- The `on radio received` block triggers every time the micro:bit gets a number from another micro:bit
+- A **variable** called `strength` is created to store the received signal strength
+- `received packet signal strength` gives the RSSI (Received Signal Strength Indicator) value
+- Variables are named containers that store information and can be used and updated later
+
+### Step 4: Interpreting signal strength (page 4)
+
+**Code added in this step:**
+
+```javascript
+if (strength > -67) {
+    // too close - less than 6 feet apart
+} else {
+    // safe distance - more than 6 feet apart
+}
+```
+
+**Key concepts:**
+- -67 dBm is the pre-measured signal strength at 6 feet (2 meters) for micro:bit Bluetooth
+- Signal strength closer to 0 = stronger signal = closer distance
+- Signal strength farther from 0 (more negative) = weaker signal = farther distance
+- `strength > -67` means the devices are **closer** than 6 feet (stronger signal than the threshold)
+
+**Common student question:** "Why -67?" Because -67 dBm was measured as the power level when two micro:bits are 6 feet apart. Different Bluetooth radios may have different values at the same distance.
+
+### Step 5: Lighting it up (page 5)
+
+**Code added in this step:**
+
+```javascript
+if (strength > -67) {
+    basic.showIcon(IconNames.Sad)    // too close
+} else {
+    basic.showIcon(IconNames.Happy)  // safe distance
+}
+```
+
+**Key concepts:**
+- Sad face = too close (less than 6 feet)
+- Happy face = safe distance (6 feet or more)
+- Icons are found in the Basic section of MakeCode
+
+For a visual reference of the final blocks code, see the screenshot at the end of the [Lighting it up](../light-it-up) page.
+
+### Step 6: Downloading the code (page 6)
+
+No new code is written. This page covers:
+
+1. **Pairing:** USB connect, click `...` next to Download, select "Pair device", click "BBC micro:bit CMSIS-DAP", then Connect
+2. **Downloading:** Click `...` again, select "Download to micro:bit", wait for "Download complete" bubble
+3. Students only need to pair once
+
+## Troubleshooting
+
+| Problem | Cause | Solution |
+|---------|-------|----------|
+| Micro:bits cannot communicate | Different radio groups | Verify all micro:bits use the same group number |
+| Always shows sad face | Signal too strong (micro:bits too close) | Move micro:bits farther apart (more than 6 feet) |
+| Always shows happy face | Signal too weak or no signal | Move micro:bits closer, check they are powered on and running the same code |
+| No face shows at all | Code not downloaded or micro:bit not receiving | Re-download code, check USB connection, verify both micro:bits are running |
+| Simulator does not respond | Signal strength not adjusted | Click and drag the yellow square wave antenna on the simulated micro:bit to change signal strength |
+
+## Extension ideas for advanced students
+
+- Change the threshold value (-67) to test different distances
+- Add a number display to show the actual signal strength value (`basic.showNumber(strength)`)
+- Use different icons or LED patterns instead of sad/happy faces
+- Add sound using `music.playTone()` when devices are too close (requires micro:bit v2 or external speaker on pin 0)
+- Create a "traffic light" system with three zones (close/medium/far) using multiple if/else conditions