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IDC Ribbon Cable Length Restriction?
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IDC Ribbon Cable Length Restriction?

by nateloaf on Sat Oct 16, 2010 7:37 am

I have to connect an LCD to an Arduino project using a 20-conductor IDC connector. For this project I might need to have the display mounted a decent distance away from the controller. Something perhaps as much as 4-8 feet. Will this length of cable cause a problem?
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Re: IDC Ribbon Cable Length Restriction?

by richms on Sat Oct 16, 2010 9:41 am

I have gone furthur than that with cat-5 cable, but I was powering the display at the display end as it was running off a printer port of a PC. even with a 20mA backlight running you will still be ok for voltage drop over those short distances.

Not too sure on noise and capacitance issues tho, but nothing lost by giving it a shot.

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Re: IDC Ribbon Cable Length Restriction?

by cstratton on Sat Oct 16, 2010 10:53 am

nateloaf wrote:I have to connect an LCD to an Arduino project using a 20-conductor IDC connector. For this project I might need to have the display mounted a decent distance away from the controller. Something perhaps as much as 4-8 feet. Will this length of cable cause a problem?


Giving it a shot is the usual first approach.

A lot will depend on the data rate and signal timing of the cable, for example, are you scanning the LCD directly or are you talking to an on-module controller?

You may want to look into transmission line termination to surpress destructive interference of reflections echoing back and forth on the cable. Source termination with a series resistor often works well in a unidirectional line with a single receiver. If you have a separate clock line and there is plenty of setup time of the data before the clock, you might get away with only terminating the clock. A scope rated several times the signaling rate would be a help to investigate.

Determining the resistor value can usually be looked up / calculated, but you need to know the geometric distance to a parallel ground. If your cable is grounded every other pin, you are in luck. There was actually a revision to the design of IDE/ATA cables when they went to a higher data rate, what they did was use half pitch cable (80 conductors instead of 40) and ground every other line in the IDC connector itself, so that they could make a cable with decent transmission line properties while remaining backwards compatible with the pinout of the original slower interface. I don't know if you can source that in longer lengths, but at 20 pins (and probably not all used) building your own transmission line cable even out of the ordinary stuff by dealing with the wires individually should be reasonable.

You could also put a microcontroller at the display and simply talk 115200 baud serial to that using some cat5 or whatever comparable cable is easy to source, pairing each signal with ground.

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Re: IDC Ribbon Cable Length Restriction?

by zener on Sat Oct 16, 2010 2:14 pm

Or maybe get a display already set up for serial interface.

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