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This page is to give you information to help with the Electronics Achievement Standard.
Part 3 Interfaces and Components
An interface is a device that fits in between a microcontroller and a sensor or actuator. The interface allows the microcontroller to accept information from a sensor, or to transmit information to an actuator. (Our actuators are usually motors or servo motors)
The interface you are most familiar with is the L293 H-bridge motor controller.
This takes information from pins 8 and 9 and 12 and 13 on your Arduino shield and sends out power to control your motors. The interface ‘understands’ what the microcontroller wants the motors to do, and puts out the power to make that happen.
Input interfaces we are using include the compass, colour sensor and sonar.
Input interfaces take information from sensors, like the compass, or the colour or colour sensor, and turn it into voltages that the microcontroller can measure.
A sonar detects a trigger signal from the microcontroller and sends out a short burst of ultrasonic waves. A short time later, it detects the echo and sends a voltage to the microcontroller uses it to measure how long the sound took to go out and back. Then it’s just maths to work out how far away the object is.
Here are some links which show how some of these things work.
The main point you need to get is that there are 9 sensors which allow red light to land on them, 9 that allow blue to land on them, and 18 that allow green light to land on them, and this allows us to measure how much red, green and blue is being reflected off our target object. Once we know that we can work out what colour we are looking at, especially when we use a map that has a limited number of colours on it. (We don’t need to worry about shades of green. We just need to know that it has plenty of green in it and it’s not red or blue or white. Limiting the colours on the map is one of the things we have done to improve the reliability of the colour sensor.)
compass A compass has three hall effect sensors, one for each of the x-, y- and z-components of the earth’s field and once we have these three numbers we can calculate the direction of the field using simple trigonometry which is what happens in the software in the compass library. You don’t need to explain it in any more detail than that.
servo Don’t worry if you don’t understand every detail of this one. Just get the main points it is making. The incoming pulses create a voltage which is compared with the voltage generated by the position sensor in the servo. If these voltages don’t match the servo turns until they do, and then it stops.
H-bridge only watch the first couple of minutes. In a real H-bridge the four switches are actually four transistors, but they act just like the switches and allow you to make the motor go forwards and backwards, and you don’t really need to explain it in any more detail than that.
If you want to get Excellence you can explain in more depth, but for Achieved you need not go into it any more than what I have described above.
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