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A complication on the "input"/"output" distinction

This page is very rough at this time. Sorry!

Not every device is simply an "input device" OR "an output device".

Take for instance the very useful DHT family of digital humidity and temperature sensors. All that I am about to say also applies to the even more useful family of chips from Dalsemi designated the "1-Wire" family... even though they need two wires, if you count the ground connection.

Many of these chips (and all of the DHT chips) are sensors. Sensors should provide INPUT to something else, of course.

However, these are fancy sensors. They need to be given commands, instructions, whatever you want to call it, FROM the thing they will SUBSEQUENTLY send input to.

But they connect to their hosts with just ONE data wire and a ground wire. (And they will sometimes... often... want a third wire to provide the voltage to bring them to life!)

So... they are neither "simply" input or output devices. That one data wire will sometimes be carrying data one way, e.g. from host (Arduino) to sensor. And sometimes the other direction. Unless you are using a NoviceGuard, to spare you some of the "details", while you get going, you should be very nervous about a wire that connects to something that is sometimes an input, sometimes an output. It is important to set things up so that inputs are fed by one sort of circuit, outputs only feed into a different sort of circuit.

Happily, the Arduino, and Arduinos with NoviceGuards, can cope quite well with the complexities which would give a novice a headache.

All of the above just to say: If you notice this possibly "dangerous" situation, where something is sometimes input, sometimes output, as long as the "thing" connected to the Arduino is "driven" by appropriate libraries, all should be well. Whew.

Oh. And it was also written in hopes of putting at rest the minds of NoviceGuard users who are puzzled by being asked to plug a sensor into a daughterboard socket which is supposed to be used for output devices. Yes: A sensor is essentially an INPUT device. But some of the fancier sensors need commands FROM the Arduino, so, they send input to the computer for only part of the time, and do, sometimes, act as something you need to send an output to. And the libraries will take care of the "I'm an input!" / "I'm an output!" stuff... and no one's nose will grow longer at any time, either.

How to email or write this page's editor, Tom Boyd. This page, and the software it references, ©TK Boyd, 8/2015.

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