The Completed Buggy

The images below show the completed buggy with all the components connected. They also show the improvements we made, such as the shield which blocks out ambient light. This final buggy also impliments the use of brighter white LED's instead of the red type used earlier. These provide better light and therefore increase the sensitivity of the LDR's. This change has lead to a significant improvement in line following performance.

Buggy Build Update

A couple of improvements have been made to the buggy in order to improve the performance of the line following.

We experienced problems with the LDR's not reading light the way we would have liked it to. Because the LDR's read all visible light, the sensitivity repeatedly changed in different ambient lighting conditions. At one time during testing the LDR's readings changed by 40 from around 100 to 60 when taking the buggy into different rooms. To solve this problem we incorperated the use of a shield which blocked ambient light from reching the LDR's. This shield was made from black card and was assembled around the two sensors. The black card reduces the reflection of the light from the LED's. This means that only light from the LED's is reflected from the white surface to the LDR's, therefore improving the line following performance of the buggy.

LED change

With the presentation looming our utter most concern is for the buggy to complete the course and this has led to some inspired last minute changes. So far throughout testing 2 red LEDs were being used with the intention of carrying these on to the presentation but unfortunately or rather fortunatelywe have discovered that we are these are causing calibration problems.

This is due to the red LED not providing enough constant elumination to the LDRs so as to maintain the same binary analogue values. This has led us to test and switch to using to white LEDs even though they are more costly. This is simplly because the illumination they give is far much superior that what we have been testing so far and therfore this should boost our line following chances and at the same time reduce the need for constant re-calibration.

Circuitry Testing

This is full circuitry connected to test the code. this is the full set up of our buggy before being assembled to the chassis and using variable resistors as part of the analogue input. Just for testing sake we first used two LEDs as outputs instead of the driver board and two motor set up. This helped us test the code without having fully assembled the buggy.

We have decided to stick to the breadboard for our circuitry instead of other options such as circuit boards or smaller bread boards and this will help us keep the costs low for our buggy. This therefore means we will have to model the chassis around the full bread board.

After tests the circuitry worked and therefore the next step was to connected it up to the motor board and motors and again this worked beautifully using simple code to test the connections, meaning we are ready for assembly and programming the code into the chip.

Cicuitry

This is the circuitry used to run our buggy. Using an analogue input of LDRs connected via two 4.7k resistors instead of variable resistors so as to give us a more steady analogue value. This is then outputted to two motors connected through the motor driver board so as to control the direction for our buggy. Two LEDs are also used connected in series as outputs so as to give illumination to the LDRs.

Care has to be taken when assembling so as to keep away from frying the delicate chips or short circuiting.

Choosing Input Sensing Method

As the objective of the project is for the buggy to follow the line, we will be using 1 of 2 inputs to send a signal to the motors when the is a change in light intensity. The choice we have is between using LDRs to send a signal when light intensity changes or Magnetic Reed Switches to send a signal when the magnetic strip is detected.

To help us make the best choice we set up a simple circuit outputting the LDR/Reed Switch to a simple LED to represent our motor.

Having carried out this test it was easy to make the decision that LDRs would be used as our input. We decided to use 2 LDRs which will be used in series with LEDs to send an input into the chip when the magnetic strip is sensed.

Using LDR's to track the black line

A line follower robot works on the same principle as a light follower robot. However, instead of tracking light the LDR (Light Dependant Resistor) is used to track the black line. This is done by programming the chip connected to the LDR to differentiate the line colour and the colour of its surroundings (in our case a black line on a white background).

It is possible to use one LDR to act as the sensing device to track the line; however the buggy would not follow the line smoothly. To improve the smoothness (resolution) of the line following, more LDR’s would need to be used.

As we are limited to the number of LDR’s we can connect to our project board the group have made a decision to use 2 LDR’s in a line combination.

The diagram above shows how the buggy could follow the black line. It uses the two LDR's (S1 and S2) to navigate its way along the line in a zig zag motion. The LDR's (S1 and S2) read the intensity of the light being reflected from the track surface. So, when S1 is directly above the black line the light intensity is low making the buggy turn left. Smilarly, when S2 is directly above the black line the light intensity is low making the buggy turn right. We could include another case where neither S1 or S2 are above the black line. When this is the case both wheels would be turning at the same rate, therefore keeping the buggy moving in a forward direction.