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Arduino boards

The purpose of an Arduino board is control. This means to take in a variety of data from devices such as switches, volume controls, light detectors and so on, and then to process the data and send it out to other devices such as motors, lamps and so on. These devices are called transducers and there is a whole page devoted to them.

There is a series of Arduino boards of varying complexity or size. By far the most common is the Uno, which is very capable and can be bought for less than £20. Clones can be bought for as little as £12, but the hole spacings and sizes are sometimes different, whereas the genuine article is always the same.

 

The board can be powered through the upper left USB port, the lower left 2.2 mm power socket into which you put 9 volts or through Vin.

Computers are very simple devices at heart. They only know one thing, a one, or its absence a zero. That's not much to know. Inside the computer a one is up to 5 volts and a zero is 0 volts. Everything has to be turned into these ones and zeroes called binary digits or bits. This is then called digital data. Arduino boards are small computers so they work on these principles.

There are two types of input - digital and analogue

There are two types of output - digital and pulse width modulated

Digital input and output

Some inputs are intrinsically digital. For example when we close a switch we can change a single zero to a single one. This sort of input needs just one socket and is called a digital input. There are fourteen digital inputs on the Arduino Uno. The same sockets can be used for digital outputs to operate lamps, run stepper motors and so on. Each can be set to be either input or output.

Analogue input

However most transducers are not digital. They produce voltages that are continuously variable between two values. Because this voltage is in proportion to the sound level, brightness etc, it is an analogy for it - a model - so it is called analogue voltage. There are six analogue inputs on an Arduino board. You can put in any voltage between zero and five, or choose a lower maximum voltage by applying it to the AREF socket. Analogue inputs have to be turned into ones and zeroes, a process called digitisation. To do this you use binary arithmetic. Here is a simple example using four bits to represent values between 0 and 15:

0000
0
0001
1
0010
2
0011
3
0100
4
0101
5
0111
6
1000
7
1001
9
1010
10
1011
11
1100
12
1101
13
1110
14
1111
15

The Arduino uses 10 bits to represent analogue voltages, so it can detect 1024 different levels. Don't worry if this means nothing to you. You can use the board without knowing about it.

Pulse width modulation (PWM)

There is a kind of analogue output as well, in fact six of them. They are on digital pins 3, 5, 6, 9, 10 and 11. Obviously you can't a use a pin for both analogue and digital at the same time. If you, for example, want to control the brightness of a lamp, the voltage is switched on and off to create an average current. If it is mostly off, the average is low so the lamp is dim. If mostly on, the lamp is bright. There are 256 different levels. This is called pulse width modulation PMW. It can also be used to control the speed of a non-stepper motor, though there are much better ways.

PWM can also be used to control servo motors of the kind used in model cars and planes. There is code for this in the library. These devices are noisy and not very powerful. They can only move things a few centimetres, but they are very cheap at about £2 and very easy to use.

Shields

Shields are additional boards that have pins sticking out. They plug into the sockets on the Arduino board. One that I find useful is the screwshield shown here. This allows you to put wires into screw terminals rather than sockets, making them more secure.

 

 

You can get a wide variety of shields including LCD and LED displays, accelerometers, motor controllers, ethernet, joystick, datalogger, bluetooth, memory card and so on.

The Arduino mini

I have just come across this superb tiny version of the Arduino. You can see just how tiny it is by comparing it with the cm rule. I think I will be using these in the final control boxes. I like having soldered joints for reliability and the size makes it easy to compact the box.

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(C) Peter Scott 2012

Last edit 23 December 2015