101 lines
3.8 KiB
Markdown
101 lines
3.8 KiB
Markdown
# Code
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Let's build the code that, when the user presses the button ``A`` on a @boardname@, will send an impulse over a wire to the receiving @boardname@ and turn an LED on there.
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Make sure that the sending and receiving wires run symmetrically across: pin ``P1`` on one @boardname@ is connected to pin ``P2`` on the other, and vice versa, as shown on the pictures in the "Make" section. This way we can use the same code on both @boardname@s .
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## Step 1
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We start with a block that digitally writes **high** (value ``1``) to the sending @boardname@'s pin ``P1``. This block can be found in _Pins_ drawer of the Advanced section.
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```blocks
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pins.digitalWritePin(DigitalPin.P1, 1)
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```
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## Step 2
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To show what we are sending, we add a block to turn on an LED in the centre of the LED display (2,2) using _plot x, y_ :
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```blocks
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pins.digitalWritePin(DigitalPin.P1, 1)
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led.plot(2, 2)
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```
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## Step 3
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Now that we know how to send the signal, we only want to be doing it while the button ``A`` is pressed.
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Pick an _if_ block from the _Logic_ drawer (you'll need the version with _else_ part that will remain empty for now). Add a check whether the button ``A`` is pressed from the _Input_ drawer and move the blocks from the previous step into _then_ part :
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```blocks
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if (input.buttonIsPressed(Button.A)) {
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pins.digitalWritePin(DigitalPin.P1, 1)
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led.plot(2, 2)
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} else { }
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```
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## Step 4
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For the _else_ branch (while the button A is not pressed) we want to do the opposite of what we did in the _then_ branch: take the value of pin ``P1`` to **low** (0) and unplot the corresponding LED on the sending @boardname@ :
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```blocks
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if (input.buttonIsPressed(Button.A)) {
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pins.digitalWritePin(DigitalPin.P1, 1)
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led.plot(2, 2)
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} else {
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pins.digitalWritePin(DigitalPin.P1, 0)
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led.unplot(2, 2)
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}
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```
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## Step 5
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Let's wrap it all in a forever loop so this code runs in the background, forever checking the button ``A`` and sending the appropriate signal to the receiver.
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Modify your code so that your code looks like this. Download the code into one of the @boardname@s, press and release button ``A`` a few times.
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```blocks
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basic.forever(() => {
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if (input.buttonIsPressed(Button.A)) {
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pins.digitalWritePin(DigitalPin.P1, 1)
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led.plot(2, 2)
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} else {
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pins.digitalWritePin(DigitalPin.P1, 0)
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led.unplot(2, 2)
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}
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})
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```
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The sending part is done, so we are going to add the receiving part.
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## Step 6
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The receiver needs to digitally read from the pin to which the sending @boardname@ will be writing (``P2``) over the wire. Let's start by going to the _Pin_ drawer, adding digital read pin ``P0`` and changing the pin value to ``P2``.
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Now we want to examine the value read from ``P2`` and check whether it is **high** (value ``1``) or not. Go to the _Logic_ drawer, first pick an _if_ block, then come back for a comparison operator (=). Plug in our digital read block as one operand and the value ``1`` as the other.
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We shall turn the LED in the bottom right corner (4,4) on to indicate that we received **high** and turn it off otherwise.
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Your code should look as follows:
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```blocks
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basic.forever(() => {
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if (input.buttonIsPressed(Button.A)) {
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pins.digitalWritePin(DigitalPin.P1, 1);
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led.plot(2, 2);
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} else {
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pins.digitalWritePin(DigitalPin.P1, 0);
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basic.clearScreen();
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}
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if (pins.digitalReadPin(DigitalPin.P2) == 1) {
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led.plot(4, 4);
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} else {
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led.unplot(4, 4);
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}
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});
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```
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Your telegraph is ready!
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## Step 7
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* Connect the first @boardname@ to your computer using your USB cable and download the telegraph script to it.
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* Connect the second @boardname@ to your computer using your USB cable and download the telegraph script to it.
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* The first person and second person can take turns pressing button A on their @boardname@s to play the telegraph game!
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