8 bits to ?????


Thread Starter

Mark Hill

Hi all;

Here's an interesting problem.

I have a client who runs 8 NO contact closures through a long cable (>50ft) to turn on/off LED's in a display bar. He'd like to reduce cabling cost.

Can someone suggest a method (widget) of converting these 8 discrete signals into something else (4 to 20, serial, ???) then converting it back to 8 bits on the other end ?


Mark Hill
[email protected]
Responding to Mark Hill's Thu, May 9, 11:33 am query:

Sounds like a job for... no, not Superman, not even Spiderman, but... PAMman. Yes the old and forgotten Pulse Amplitude Modulation circuit.

For some guidance, check Radio Shack's "Getting Started in Electronics"! Another reference is Don Lancaster's "CMOS Cookbook" published by Howard
W. Sams & Co.!

Phil Corso, PE
(Boca Raton, FL)
Thanks Paul but the cost of the cabling is a minor part of the whole problem. He uses 18awg shielded throughout his systems with large mil
spec water tight connectors. How about the cost of 4 connectors and the labor to solder/test the
whole mess. Then often, the field tech has to cut off one end in the field, adjust the cable length, then wire it back together.

Lots more cost other than a chunk of wire.

You can use AS interface used by a lot of automation equipments ie Siemens. It is used for distributed I/O devices and is working by interchanging field signals on the same 2 wires which are powering the field I/Os with 24Vcc.
Omron (and others?) make several complete lines of digital "MUX" products. You'd just put an Input module at one end, run 2 wires over to an Output module at the other end. These guys just move/echo the status they see at the other end.


Lynn August Linse, Senior IA Application Engineer
15353 Barranca Parkway, Lantronix Inc, Irvine CA 92618
[email protected] www.lantronix.com
Tel: (949)279-3969 Fax: (949)453-7152
Further to Mark Hill's query:

If you don't want to design your own Xmit & Rcvr circuits, then I suggest you contact "BitLink" of Denmark. They have a series of solid-state and semiconductor DIN-rail modules.... 8-bit is a standard unit.

Phil Corso, PE
(Boca Raton, FL)
We have a small module that can take 8/15 inputs, igital output a serial stream and at the other end a corresponding module to convert it back to 8/15 outputs.

These are multiplexing and demultiplexing modules meant for transfer of signals over 2000 meters. Our focus is on serial transfer of signals over wide area, dealing in clumps of signals in density of as low as ONE.

the modules are normally sold LP ex-works at equiv. of 100 USD a pair for 8 I/Os and USD120 per pair for 15 I/Os. We use transfer over standard wires, preferably shielded (not really needed by our system, but we notice, the pair of wires is left unscathed in the field when it looks shielded, else someone tries to check if its apower cable!!

let me know if you need further info on these.

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