Catagories of Contact

Contents of this page:

1. Input
   • Digital Input
   • Analog Input
2. Output
   • Digital Output
   • Analog Output

Also See Transducers and I/O Devices
MAIN PHYSICAL COMPUTING PAGE

INPUT

This is the most common thing that people want to add to their interactive projects. Suppose you want something in the physical world like picking up a coffee cup or shining a flashlight on a wall or pulling a rope to trigger or contol something in your computer. You need some extra input. Because multimedia computers have such versitle output sometimes a little extra input is all you may need.

Digital Input.

Digital Input can cover a lot of the actions in the physical world and it is the easiest to engineer. For instance if you want to know whether or not a person is standing on a carpet then all you need is a digital input. A digital input will work when the action in the physical world has only two states that you care about, for instance they are are either on the carpet or they are off the carpet, the switch is up or down, a hat is on or off, the tounge is in or out. As you can imagine true or false information is very easy for the computer to accept. The transducers for digital inputs are usually switches or one kind of another.

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Analog Input.

Sometimes you are trying to find how much something is happening in the physical world. For example you might want to know how heavy the person standing on your carpet is. A simple true or false won't work and you need some analog input. Because we are using computers, this analog information must eventually be encoded in a digital form, usually a number between 0 and 255. Your microcontroller might have a built-in A/D (analog to digital) converter or can fake it using an R/C (resistor capacitor) circuit. The easiest and best transducers for analog input are variable resistors of one kind or another.

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OUTPUT

Suppose you want a physical light to turn on or off or a toy car to go faster or slower depending on mouse movements in the computer. This requires some extra output. Output can be more difficult than input for some people because it often requires electrical (as opposed to electronic) or mechanical skill. If you are the type of person who likes making or collecting and arranging physical objects, then it will be a blast.

Digital Output.

If you want to turn an electric fan on or off or turn a dolls head around then all you need are some digital outputs. Digital output will work when the thing you are trying to effect has only two possible states. In engineering digital outputs you typically get control of things by interrupting with the normal flow of electricity with a switch just like you would for a light switch in your home. In order for the computer instead of your finger to contol the switch you use special switches that can be electronically thrown, like transistors or relays.

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Analog Output.

If you want to vary the degree of output, for example, decide how fast the doll's head is spinning or how bright the light is, then you need some analog output. Because the computer is a digital device, you will need a D/A (digital to analog) converter which many microcontrollers have built in or you can fake it with something like PWM (pulse width modulation). The analog output of a microcontroller is not really enough to power anything so most applications will require more circuitry. There are a few simple things that you can use without a lot of extra circuits.