MIDI over long cable runs
jezz at enterprise.net
Tue Jul 21 11:53:48 CEST 1998
>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
>that 30 to 40 feet is about the limit for reliable MIDI communication,
>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
>on the list ever made such a box?
>I was thinking that it might be possible to use some of those RS232
>driver/reciever chips, such as the MC1488 and MC1489. The level-shifted
>differential signal would be sent down a standard XLR microphone cable.
>this sound feasable? Are those chips fast enough for reliable MIDI data
>transfer? What voltage level would you recommend that I use for the
>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
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