Re: [midatlanticretro] Re: Intellec 4 MOD 40 working!
- I fully intend to start my own web page soon. I may even try hosting it myself. We'll see how long I can do that before Charter complains. I have so much I can put on a web page, and it's just a matter of doing it at this point.I was purely joking about the teletype. Indeed, it was one of the few options available at the time, and a far cry from what you could do with the front panel on the 4 MOD 40. Even a couple of years later, the SWTPC 6800 still had a serial board that would fully support the 20mA current loop for teletypes.Thanks for the link regarding the current loop to TTL converter. I have a bunch of 4N28s, so I suspect a couple of those, a MAX232, and tapping "5V" off the 5V line through a 220 ohm resistor (the high side of the input current loop on the Intellec) will be sufficient. Of course, I'll have to test it before I can say this will work for certain. I may be able to put a rather large capacitor on the Vcc line of the MAX232 to keep the voltage a bit higher during times of high load.KyleOn Tue, Nov 13, 2012 at 3:57 PM, s100doctor <hjohnson@...> wrote:This is a fantastic find! I've wanted a MOD 80 for a long time. I have some MOD 40 stuff. When time permits me, I'll chat with you about Intellec stuff. But I hope you make up some Web pages about these two computers to document them and your work.
--- In email@example.com, Kyle Owen <kylevowen@...> wrote:
> I was given two Intellecs, a 4 MOD 40 and an 8 MOD 80, a little over a week
> ago. Both are in phenomenal condition. They were bought from surplus in the
> early-to-mid 1980s and stored for the next 30 years, not ever even turned
> on within that time period.
> Does anyone have a simple design for a 20mA current loop to RS-232
> converter they would share? The Intellec unfortunately only offered current
> loop, since that I guess was the "hip" thing at the time. After all, who
> wouldn't want to type in their software and get the printout at a blazing
> 110 baud? :)
Here's some preserved information about another computer, made not too much after the MOd 80 was available:
The manual for it has a current loop to CMOS/TTL converter design, and a description of it, on page 63-65 of the PDF:
You may have to adjust the components for +5/-5v or +12/-12v operation but you may well get away with +5/0v. Just be sure that a RS-232 negative level (transmit low) doesnt' forward bias that base-emitter junction on Q1 and fry the transistor with too much current. This calls for a little transistor theory...
Circuits like these, depend a little on the voltage of your current source. I don't know if the Intellec has a current loop supply, or what it expects, see the docs. But in general, it's typical to use optoisolators to keep nasty current loop voltages (and electrical noise from TTY's) away from your microcomputer.
- On 11/13/2012 02:18 AM, Kyle Owen wrote:
> I was given two Intellecs, a 4 MOD 40 and an 8 MOD 80, a little over aBeautiful! I covet the 4/40. If I can ever pry it out of your hands
> week ago. Both are in phenomenal condition. They were bought from
> surplus in the early-to-mid 1980s and stored for the next 30 years, not
> ever even turned on within that time period.
> They were originally going to go in a computer memory display, but they
> didn't quite fit in, nor was there quite enough room for them. Since
> that fell through, they came into my hands as someone who was willing to
> clean them up and get them working again.
> I have only a couple of issues with the 4 MOD 40, which is the only one
> I've cleaned up and actually gotten working at this point. One LED (bit
> 0) on the address indicator flickers sometimes, and another LED (bit 9)
> is completely dead. I'm not sure if it's a resistor, LED, or driver yet,
> but I'll be doing some more debugging this weekend, probably.
> Anyways, here's the album: http://imgur.com/a/2s18f
with some tasty trade action, do let me know.
Dave McGuire, AK4HZ
New Kensington, PA