Serial wiring

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Nick U
Posts: 4
Joined: Tue Oct 27, 2015 8:13 pm

Serial wiring

Post by Nick U »

A quick question about 232 serial communication wiring (my instrument panel upgrade).

As I understand it, a serial line carries the signal and the return line is usually the ground (serial return).

— How important is it to use a shielded wire for the EFIS? The EFIS manual no mention is made of using any shielded wires. I assume one can wire the EFIS / AHRS using a single strand wire with the common ground on each piece of equipment as the return. Another possible is using a shield wire with a ground at one end of the braided shield and floating the other end.

Or does it matter which way you chose since both accomplished basically the same thing with the GRT products?

NOTE: the length of the serial wires (with the exception of the magnetometer will not exceed 2 ft.

Thanks!
Bobturner
Posts: 444
Joined: Mon Mar 11, 2013 6:34 pm

Re: Serial wiring

Post by Bobturner »

Well, it is hard to criticise for being too careful. As you know, a shield terminated at one end only is best for shielding the RS232 wire from unwanted pickup; a parallel wire (or the shield) carrying the return current is best for reducing emissions from the RS232 wire. For the latter, many pieces of equipment internally ground the RS232 return, so it's not possible to direct all the return current down the shield or parallel wire. As far as interference to the RS232 signal, these signals are 'high level', e.g., many volts. It's pretty unusual to experience that level of unwanted pick up. So... I just used one unshielded wire for short connections behind the panel. Shielded for longer runs. ymmv.
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