B - Robot Police

We're going to be using a lot of modules to turn our robot into a police car!

Carefully assemble your robot like the picture. The connections should be:

Buzzer > P2

Switch > P1

Sparkles > P0

Left Motor> M1

Right Motor > M2

Now we know how to use the sparkle module, let's start by programming all the sparkles to flash red and blue like a police car.

Your program should:

Turn all sparkles red

Wait half a second

Turn all sparkles blue

Wait half a second

Repeat this forever!

Make sure to test your program works.

Let's add the buzzer to the flashing lights to make a siren!

Add some lines to your program so the buzzer is:

Buzzing when the sparkles are red

Off when the sparkles are blue

There are some hints in the picture if you can't remember which functions to use!

Police cars don't have their lights and sirens on all the time, that would be very irritating!

Let's add a switch so the police robot only flashes and buzzes when we press it.

Add an IF statement that checks if the switch is pressed, and move your sparkle code inside the IF statement so it is run only when the switch is pressed.

Don't forget, make sure all your code is inside a while True: loop so the switch isn't just checked once!

Test out your program - does it work how you expected?

Currently, the siren and lights only run once when we press the switch. We really want them to run forever when the switch is pressed!

We need to use another loop for this - luckily we can use a while loop!

Don't forget - a while loop will run all the time the condition is True

For example, the while loop in the picture will run until the switch is pressed!

Inside the if statement, put your sparkle code inside a while loop that will run forever.

Now we can activate the police robot with the switch, but we can't turn it off again!

We need to change the while loop, so it only runs until the switch is pressed again.

Change the condition in the while loop so it uses a read_digital function to only run until the switch is pressed.

Test it out - does it work as expected?

The picture has an example of what the code should look like before this step!

You might find it doesn't work very well, and it sometimes takes a few attempts to turn the lights on or off.

Our problem is that the robot runs the program very, very fast!

Even if we just tap the switch, the robot thinks so quickly it thinks we are holding it down.

Look at the simplified version of the code in the picture:

As soon as we press the switch, the conclusion of the if statement is run

The robot checks the condition of the while loop before we can possibly have time to take our finger off the switch, so the loop is never run (the condition is false as P1 is still 1), and the program goes back to the red arrow

This can happen many times before we have released the switch, so we have no idea whether the lights will be running or not!

This can be hard to understand! Let's make another short program to understand this problem with an example.

Save you program as a separate file and build the program in the picture.

This program turns the sparkles red if we press the switch, then blue if we press it again - test it out!

It is impossible to accurately make the sparkles red or blue, as the robot is too fast - we need to make it wait for us to let go of the switch to fix this.

Luckily, we can use a empty while loop to wait until we let go of the switch.

A while loop with no code in it will simply stall the program (wait) until the condition is false.

We need to add pass inside the loop as it can't be completely empty - the pass line doesn't actually do anything though.

We want to wait until the switch is released (reads 0), so our condition should be pin1.read_digital()==1

Go back to your police car program, and add this empty while loop into your program, right at the start of the if statement.

We need to do the same thing after the while loop that flashes the sparkles, so when we press the switch to turn them off they don't get started again immediately!

Add another empty while loop like the first one at the end of the if statement.

You may have noticed that the sparkles stay blue after we turn off the police lights and siren - let's change them so they are green!

Add some more sparkle lines so that:

The sparkles are set to green at the start

They are reset to green after the end of the main while loop.

The final part of our police program is to make the robot chase after our criminal!

Check the picture for what your code should look like so far.

Add some code to make your robot drive forwards at full speed when the switch is pressed and the sparkles are flashing, then stop when it is pressed again.

For this extension challenge, you need to complete a few tasks:

Change the buzzer code so that your buzzer beeps faster than the sparkles change to make it sound more realistic.

When your robot is chasing the criminal, make it turn left and right in a weaving motion instead of just moving forwards.