20 Apr
2025
20 Apr
'25
6:24 p.m.
Wikipedia says it was defined in 1960 although their cite links don’t seem to work.
If that helps!
Sent from my iPhone
On Apr 20, 2025, at 08:01, Chuck Guzis via cctalk
<cctalk(a)classiccmp.org> wrote:
On 4/20/25 04:11, Steve Lewis via cctalk wrote:
Anyway, just poking around, no specific question
here :) Wel, except a
related/unrelated question -- why does MIDI use 5mA current loop? And is
that why MIDI adopted the joystick port? (IBM original joystick card spec,
didn't it involve measuring electrical discharge? so it is effectively a
current-loop port? is that somewhat accurate?)
Having occupied an adjacent building to Sequential Circuits on N. First
Street, right after the orchards were bulldozed, my guess is that 5 ma
was completely satisfactory for the relatively short haul that MIDI
required sometime around 1980.
Note that old (<Model 15) TTYs used 60 ma current loop and were strictly
mechanical devices. 60 ma could adequately power the selector magnets
in 1930,
--Chuck