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This is mostly a hardware question but with interesting software implications:

Parallel ports are one of the wonders of the age. As well as printing things you can use them to control external devices, for example, by switching reed relays on and off simply by writing the correct word to the parallel port buffer.

And they are really cheap. A reliable USB-parallel cable can cost you no more than £5. So you can build a very neat, software controlled system capable of switching 8 things on and off for less than £10 (because there are 8 data bits available on a standard parallel interface).

You can increase the number of things you can switch by adding more parallel ports. At £5 each that's still cheap. But what if I want to build a really big multiplexer - controlling 128 lines, for example? That requires 16 parallel ports - starting to get cumbersome to handle and to code, with lots of opportunities for hardware and software glitches.

So are there any interfaces (legacy or otherwise) which do the same job but, for example, with two bytes or more, so that I can reduce the number I need to use?

Yes, I do know that I can control pins other than the 8 data pins on a parallel port. That provides some further lines of control. But surely there is some nice, cheap port which has 16bits or more available in parallel?

All thoughts and advice warmly welcomed.

D.Jordan
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I'm not sure why this is on stack overflow and not say electronics.se or arduino.se etc. The answer is you can switch over to serial ports. See your USB is already a serial port so your data travels trough a serial cable and is converted parallel. There's no reason why one paralel port can only split 8 values, it can split as many as you want. (limited only by your sampling speed requirements)

For about 5-20 euros worth of components you can easily build your own electronics. A bogstandard arduino gives you 13 lines. But you can easily extend that with shift registers. Of course using a several cheap micro controllers connected to any addressable serial communications bus could be better.

Also there are special multiplexer chips available and systems that can make sure the samples are taken simultaneously. So for example you could use a Maxwell 81840

joojaa
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