added voting project

docs/projects/voting-machine.md

@@ -0,0 +1,77 @@
+# Voting Machine
+
+### ~ avatar
+
+Build a vote collection system using many micro:bit!
+
+### ~
+
+https://youtu.be/77HOqf8BaNg
+
+
+In this project, a **voter** program is uploaded on the player's @boardname@. The player uses the buttons to vote yes or no 
+and the vote sent to the **dashboard** @boardname@ via radio. The dashboard allocates one LED per player and turns it on for "yes" and off for "no".
+
+Both programs set their radio group to ``4`` to be able to communicate.
+
+## The voter program
+
+Assuming button ``A`` is no and ``B`` is yes, the voter program works as follows:
+
+* when button ``A`` is pressed, a number ``0`` is sent via radio and the ``X`` symbol is shown on the screen.
+
+```block
+input.onButtonPressed(Button.A, () => {
+    radio.sendNumber(0)
+    basic.showIcon(IconNames.No)
+})
+```
+
+* when button ``B`` is pressed, a number ``255`` is sent via radio and the ``Y`` symbol is shown on the screen.
+
+```block
+input.onButtonPressed(Button.B, () => {
+    radio.sendNumber(255)
+    basic.showIcon(IconNames.Yes)
+})
+```
+
+* In order to track the votes, we tell the radio to also transmit the device serial number.
+
+```block
+radio.setTransmitSerialNumber(true)
+```
+
+* we arbritrarily choose ``4`` as the group used for the communications
+
+```block
+radio.setGroup(4)
+```
+
+Combined together, the voter program looks as follows:
+
+```blocks
+input.onButtonPressed(Button.A, () => {
+    radio.sendNumber(0)
+    basic.showIcon(IconNames.No)
+})
+input.onButtonPressed(Button.B, () => {
+    radio.sendNumber(255)
+    basic.showIcon(IconNames.Yes)
+})
+radio.setGroup(4)
+radio.setTransmitSerialNumber(true)
+basic.showIcon(IconNames.Ghost)
+```
+
+## The dashboard
+
+The dashboard code can be found at [/examples/radio-dashboard](/examples/radio-dashboard).
+
+Download the code from that example into the @boardname@ that will be used to display the result.
+
+When the dashboard receives a message from a @boardname@, it find a pixel for that board (and remembers it)
+and uses the number received as the brightness of the LED.
+
+When a message hasn't been received by a board for some time, it's pixel will start to blink. After more time, it will simply turn off. 
+