C - Smoother Line Following

We just need the line sensor for now - make sure your robot is setup like the picture.

To make a smoother, better line follower, we need to use the line sensor in analogue mode.

So far, we have been using it as a digital sensor - it can only be ON or OFF (HI or LO).

Analogue inputs (and outputs) can have any value - think about the difference between a digital and an analogue clock

A digital clock must display a whole number of minutes

But on an analogue clock, the minute hand can be anywhere - even halfway between two minutes!

Build the simple test program in the picture.

You can find the analogue block in the Input/Output menu

Program your robot, and keep it plugged in.

Try moving the robot slowly from one side of the line to the other, whilst watching the value of t in the variables menu.

See how it changes gradually as you approach the line?

We can use this gradual change to smoothly change the amount the robot turns as it get further from the line!

Add two new variables to the program called L and R (left and right).

Let L = the analogue value of the left sensor, and R = the analogue value of the right sensor.

Program the robot and try moving it slowly across the track again whilst still plugged in - make sure L and R behave how you expect them to!

The larger the difference between L and R, the further the robot is from the line so the more we need to turn.

For example, if both sensors are on the line, we don't need to turn at all and L and R will have the same value.

Add a new variable called turn.

After getting the values of L and R, set turn equal to the difference between L and R.

Program your robot and watch what happens to the value of turn as you move it across the line. It should be 0 when the robot is exactly on the line!

Let's use the turn variable to set the speeds of the motors.

Change the motor blocks so they use the turn variable to set the speed like the picture.

Test it out - this should follow the line really smoothly!

Do you understand how the code works? (hint: turn is positive when we need to turn right, and negative when we need to turn left)

If you robot can't do the really tight turns, try multiplying turn by 2!

You might have noticed that while the new program is smooth, it isn't as fast as the old two sensor digital program.

To make it faster, we need to make sure 1 wheel is always going 100% forwards, and then change the speed of the other wheel only based on how large turn is to follow the line.

So, if turn is positive, we should be turning right, so motor 1 should be at 100%

If turn is negative, we should be turning left so motor 2 should be at 100%

Add an IF/ELSE block to check if turn is positive or not, and set the correct motor to 100%.

Now its over to you!

Add two more motor blocks into the IF/ELSE block to set the other motor's speed using the turn variable, for turning left and right

Test the program really well - experiment with multiplying turn by different amounts to get a reliable line following program.

Here's a hint if you're confused - for the first part where motor 1 is at 100%, motor 2 should be set to forwards at a speed of 100 - turn.

If you're feeling really advanced, add the Sparkle module back in and set the colours of the LEDs proportionally based on how far away from the line the robot is!

Your robot can also get lost and now has no way of finding the line again - try and add the code you wrote previously back in so the robot can't get lost, or at least stops if it loses the line completely.