C - Morse Code Machine

So far, we have only used outputs - things that the robot can change to HIGH or LOW.

Inputs work in a similar, but opposite way - they can send a HIGH or LOW signal back to the robot!

Our program then needs to decide what to do, depending on whether the signal is HIGH or LOW.

The switch module is a great example of an input - when one of the switches is pressed, the pin it is connected to will go HIGH.

Assemble your robot like the picture. The connections should be:

Red LED - a1

Green LED - b1

Switch - c1

Buzzer - d1

We now have 4 things connected, so we need 4 pinMode lines!

The switch is an INPUT, and the rest are OUTPUTs.

Add in 4 pinMode lines to a blank program like in the picture to setup our inputs and outputs.

To use an input, we need to read it to see whether it is HIGH or LOW.

We can use the digitalRead function for this - it only takes 1 input, which is the pin you want to read.

In our case, this is c1!

digitalRead will return HIGH if the switch is pressed, and LOW if it isn't.

To use an input, the robot needs to know how to make a decision.

We can do this with an If statement!

An If statement has two parts:

Condition - this is a test, and it goes in the normal brackets after the if. It will usually test if something is equal to something else - here we are seeing if a1 is HIGH.

Conclusion - this some code inside the curly brackets, that is only run if the condition is true.

Make the program in the picture - it tests if the switch is pressed, and then turns on the red LED if it is.

Test it out - does it do what you expect?

You may have found the LED only turns on if you are holding the switch when you press the run button.

This is because the switch is only checked once - in the setup!

Move the if statement to the loop, and test it out again - this way, the switch is checked every time the loop is run.

The LED should now turn on when you press the switch!

Let's add some more code so the LED turns off when we let go of the switch!

Add another if statement into the loop, that checks if the switch is LOW and then turns off the red LED.

Your LED should now be controlled by the switch!

Often, we want to do one thing if something is HIGH, and something else if it is LOW, like turn on/off the LED.

We can use two if statements, but there is a shorter way - using an else.

Replace your second if statement with an else, to make an if/else statement:

If the condition is true, the code inside the if statement is run

If the condition is false, the code inside the else statement is run.

Your LED should still be controlled by the switch, but the program is simpler!

You may have noticed we have actually made our own Morse Code machine already!

By holding down the switch for a long time you can send a dash, and a short press would send a dot.

For this challenge, add some more code so that:

When the switch is pressed, the green LED and buzzer are on

When the switch isn't pressed, only the red LED is on.

Time for a harder challenge!

Using the Morse Code video from the first step, can you send a secret message to your neighbour?

Get them to decode it and see what they come up with - no speaking allowed!

A super hard challenge now - can you write a program that sends Morse Code for your initials (or even your whole name) automatically, but only when you press the switch?

If you're feeling really clever, try and use some loops to reduce the length of your program if you need to send lots of dots or dashes in a row.