tingo
Veteran Member
Did anything come out of this?
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RS-232 to Current Loop Interface
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ardent-blue
Experienced Member
- Joined
- Jan 2, 2015
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I -assume- this was for the 5170 adapters?
Chuck(G)
25k Member
5150, if memory serves. There's a DIP plug on the async card. Plug it in one way, you get RS232, flip it upside down and you get current loop. My old Faraday A-Tease 286 had a similar option to do RS422 instead RS232.
bburley
Experienced Member
Thought I would toss this bit out there 
The last time I played with a 20mA loop was to drive an ASR-33 as a printer. It would have some stability and timing issues so I wound up using a 150VDC source for the loop supposedly for "fast strike time". It did seem to work better, but I also remember having to replace a plastic coupler of sorts with a fabricated metal one so it would hold up while I was driving it so hard. I also remember the smell of hot oil
I don't have any specifics of how I did that handy at the moment, but maybe something will turn up as I continue to dig through my collection
The last time I played with a 20mA loop was to drive an ASR-33 as a printer. It would have some stability and timing issues so I wound up using a 150VDC source for the loop supposedly for "fast strike time". It did seem to work better, but I also remember having to replace a plastic coupler of sorts with a fabricated metal one so it would hold up while I was driving it so hard. I also remember the smell of hot oil I don't have any specifics of how I did that handy at the moment, but maybe something will turn up as I continue to dig through my collection
Hugo Holden
Veteran Member
The AIM-65 had a TTY loop drive, no optical isolation though.
When ABM made the AH5050 disk filer system, they added a serial interface on the board to gain an RS232 link, and they used an optocoupler. Only +/- 5V a little borderline for RS232.
So its more of a current loop to RS-232 than the reverse, but the circuit may be of some interest.
The circuit they used is here on post #6 they used the ICL 7660 to get the -5V rail:
When ABM made the AH5050 disk filer system, they added a serial interface on the board to gain an RS232 link, and they used an optocoupler. Only +/- 5V a little borderline for RS232.
So its more of a current loop to RS-232 than the reverse, but the circuit may be of some interest.
The circuit they used is here on post #6 they used the ICL 7660 to get the -5V rail:
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Chuck(G)
25k Member
+5 for 20 ma current loop is indeed marginal. Even +12 is for many applications; +24 is more common.
It's convenient to think of it in the same way that one thinks of driving LEDs--the critical factor is the current; voltage is adjusted to provide the stated (e.g. 20 ma or 60 ma) current. The benefit is that such transmission is relatively immune to line capacitance and induced noise effects MIDI is another such interface.
In industry, short-haul modems (SHM) convert EIA RS232C levels to current loop and back again. ref. Such connections are spec-ed in the "miles" not "feet" range.
It's convenient to think of it in the same way that one thinks of driving LEDs--the critical factor is the current; voltage is adjusted to provide the stated (e.g. 20 ma or 60 ma) current. The benefit is that such transmission is relatively immune to line capacitance and induced noise effects MIDI is another such interface.
In industry, short-haul modems (SHM) convert EIA RS232C levels to current loop and back again. ref. Such connections are spec-ed in the "miles" not "feet" range.