MIDI over long cable runs

[Jeremy Brookes]

>I find myself in need of a device that allow me to transmit MIDI data over
>very long cable runs (a couple of hundred feet).  Past experience has 
shown me
>that 30 to 40 feet is about the limit for reliable MIDI communication, 
using
>standard MIDI hardware.  There are a couple of companies who make and sell
>boxes which will send/recieve MIDI over long cables (J.L. Cooper is one of
>them), but I would much rather build my own, if at all possible.  Has 
anyone
>on the list ever made such a box?
>
>I was thinking that it might be possible to use some of those RS232 
interface
>driver/reciever chips, such as the MC1488 and MC1489.  The level-shifted
>differential signal would be sent down a standard XLR microphone cable. 
 Does
>this sound feasable?  Are those chips fast enough for reliable MIDI data
>transfer?  What voltage level would you recommend that I use for the 
driver
>signal?  Are there other interface chips which I should consider using?

You might want to look at driving the lines with RS485 or RS422 as these 
can drive much further (~1200m) than RS232 (~15m). Just convert the MIDI 
input signal with a standard opto coupler circuit to a TTL signal to drive 
a RS485 chip. Drives into twisted pair cables with a 120ohm termination at 
either end. You can even tap off at any point as it is a multi drop 
interface. Should be dead simple and cost peanuts.

Contact me if you want more details on RS485.

mailto:jezz at enterprise.net
http://homepages.enterprise.net/jezz/