Red light green light radio game (#1438)

* added new game

* added suggestion

* updated summary

* added tips

* RSSI info

docs/SUMMARY.md

@@ -47,6 +47,7 @@
     * [Light Level Meter](/projects/light-level-meter)
     * [Radio bridge](/projects/radio-bridge)
     * [Snap the dot](/projects/snap-the-dot)
+    * [Red light green light](/projects/red-light-green-light)
 
 ## #examples
 

docs/projects/radio-games.md

@@ -28,16 +28,16 @@ Here are some cool projects that you can build with your @boardname@!
   "url": "/projects/fireflies",
   "description": "Simulate fireflies with micro:bits, try it in the dark!",
   "imageUrl": "/static/mb/projects/fireflies.png"
-}, {
-  "name": "Infection",
-  "url": "/projects/infection",
-  "description": "An epidemic has broken out, see who will survive.",
-  "imageUrl": "/static/mb/projects/infection.png"
 }, {
   "name": "Hot or Cold",
   "url": "/projects/hot-or-cold",
   "description": "Find the hidden player by seeing if your close or not.",
   "imageUrl": "/static/mb/projects/hot-or-cold.jpg"
+}, {
+  "name": "Red Light Green Light",
+  "url": "/projects/red-light-green-light",
+  "description": "Play the classic game with your @boardname@.",
+  "imageUrl": "/static/mb/projects/red-light-green-light.png",
 }, {
   "name": "Voting Machine",
   "url": "/projects/voting-machine",
@@ -48,5 +48,10 @@ Here are some cool projects that you can build with your @boardname@!
   "url": "/projects/rps-teams",
   "description": "The Rock-Paper-Scissors game with lots and lots of players.",
   "imageUrl": "/static/mb/projects/rpsteams.png"
+}, {
+  "name": "Infection",
+  "url": "/projects/infection",
+  "description": "An epidemic has broken out, see who will survive.",
+  "imageUrl": "/static/mb/projects/infection.png"
 }]
 ```

docs/projects/red-light-green-light.md

@@ -0,0 +1,212 @@
+# Red Light Green Light
+
+This is a classic game where the game master is looking the opposite direction and saying commands to player.
+When the game master says "red light" and turns around, all players should stop. If the game master stops a moving player, he has to go back to the start.
+When the game master turns around and says "green light", all players move and try to touch the game master.
+
+In this remake, we will use @boardname@, the radio and the accelerometer to enforce those rules!
+
+## The game master
+
+Let's start with the code running on the game master @boardname@. Don't use this code for players!
+
+### States
+
+We define two states, ``GREENLIGHT`` and ``REDLIGHT`` and a ``state`` variable to store the current game state.
+When the game master presses ``A``, the game goes into "green light" mode. When he presses ``B``, 
+the state goes in "red light" mode.
+
+```blocks
+let REDLIGHT = 0
+let state = 0
+let GREENLIGHT = 0
+GREENLIGHT = 1
+REDLIGHT = 2
+```
+
+### Communication
+
+The radio group is set to ``1``. We will set the same group in the player code. The game state is streamed in a forever loop so that players receive constantly.
+
+```blocks
+let state = 0;
+radio.setGroup(1)
+basic.forever(function () {
+    radio.sendNumber(state)
+})
+```
+
+### Red light, green light
+
+Use the ``||radio:on button pressed`` block to run code when button ``A`` and ``B`` are pressed.
+When ``A`` is pressed, the game goes into ``GREENLIGHT`` mode. When ``B`` is pressed, the game
+goes into ``B`` mode. We also use ``||basic:show icon||`` to display the current state.
+
+```blocks
+let REDLIGHT = 0
+let state = 0
+let GREENLIGHT = 0
+input.onButtonPressed(Button.A, function () {
+    state = GREENLIGHT
+    basic.showIcon(IconNames.Yes)
+})
+input.onButtonPressed(Button.B, function () {
+    state = REDLIGHT
+    basic.showIcon(IconNames.No)
+})
+GREENLIGHT = 1
+REDLIGHT = 2
+```
+
+### Game master code
+
+All together the game master code looks like this:
+
+```blocks
+let REDLIGHT = 0
+let state = 0
+let GREENLIGHT = 0
+input.onButtonPressed(Button.A, function () {
+    state = GREENLIGHT
+    basic.showIcon(IconNames.Yes)
+})
+input.onButtonPressed(Button.B, function () {
+    state = REDLIGHT
+    basic.showIcon(IconNames.No)
+})
+GREENLIGHT = 1
+REDLIGHT = 2
+radio.setGroup(1)
+basic.forever(function () {
+    radio.sendNumber(state)
+})
+```
+
+### ~ hint
+
+Make sure to rename this program to ``game master`` or something so that you don't confuse it with the player program!
+
+### ~
+
+### Improve the game
+
+* Use ``||music:ring tone||`` to play a sound while the game is in ``GREENLIGHT`` mode.
+* Attach a servo and move the arm based on the game state
+
+## The players
+
+The code for players needs to listen for the game master state.
+
+### States
+
+First, we redefine the state constant, ``GREENLIGHT``, ``REDLIGHT`` and set the radio to ``1``. 
+We also add a ``state`` variable that will store the state of the game.
+
+```blocks
+let RED = 0
+let state = 0
+let GREEN = 0
+GREEN = 1
+RED = 2
+radio.setGroup(1)
+```
+
+### Communication
+
+We use the ``radio:on received number`` block to store the game master state into the ``state`` variable.
+
+```blocks
+let state = 0
+radio.onReceivedNumber(function (receivedNumber) {
+    state = receivedNumber
+})
+```
+
+### Display
+
+In a forever loop, we display different icons based on the game state. Use a ``||logic:if||`` and
+``||basic:show icon||`` blocks to display the game state.
+
+```blocks
+let REDLIGHT = 0
+let state = 0
+let GREENLIGHT = 0
+basic.forever(function () {
+    if (state == GREENLIGHT) {
+        basic.showIcon(IconNames.Yes)
+    } else if (state == REDLIGHT) {
+        basic.showIcon(IconNames.No)
+    }
+})
+```
+
+### Movement check
+
+If the ``state`` is equal to ``REDLIGHT``, we need to check that the player is not moving. 
+This is where the accelerometer comes into play. The accelerometer measures forces applied to the @boardname@.
+If the player moves, it is likely that some small forces will be applied and the accelerometer will detect it.
+At all times, gravity is applied to the @boardname@, so the acceleration strength at rest always near ``1000``mg.
+If the acceleration strength is far from that value, say ``1100`` or ``900``, we can assume that the player is moving. To compute this we use this formula:
+
+    moving = | acc strength - 1000 | > 1000
+
+Now that we know the math, we can turn this into code.
+
+```block
+let REDLIGHT = 0
+let state = 0
+let GREENLIGHT = 0
+let moving = false
+if (state == REDLIGHT) {
+    moving = Math.abs(input.acceleration(Dimension.Strength) - 1000) > 100
+    if (moving) {
+        game.gameOver()
+    }
+}
+```
+
+### Player code
+
+All together:
+
+```blocks
+let moving = false
+let REDLIGHT = 0
+let state = 0
+let GREENLIGHT = 0
+radio.onReceivedNumber(function (receivedNumber) {
+    state = receivedNumber
+})
+GREENLIGHT = 1
+REDLIGHT = 2
+radio.setGroup(1)
+basic.forever(function () {
+    if (state == GREENLIGHT) {
+        basic.showIcon(IconNames.Yes)
+    } else if (state == REDLIGHT) {
+        basic.showIcon(IconNames.No)
+    }
+    if (state == REDLIGHT) {
+        moving = Math.abs(input.acceleration(Dimension.Strength) - 1000) > 100
+        if (state == REDLIGHT && moving) {
+            game.gameOver()
+        }
+    }
+})
+```
+
+### ~ hint
+
+Make sure to rename this program to ``player`` or something so that you don't confuse it with the game master program!
+
+### ~
+
+
+### Tuning
+
+Does the movement check work? Try changing the ``100`` value to tune the detection sensivity. Try ``64``.
+
+### Improve the game
+
+* Use ``||music:ring tone||`` to play a tone while in green mode.
+* Use the packet signal strength to detect that you've reached the game master.