Hoglet's Past Projects #1 - the Modem

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hoglet
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Hoglet's Past Projects #1 - the Modem

Post by hoglet » Sun Aug 25, 2013 8:27 pm

Hi all,

I thought I would post a short series of articles describing some of my projects from the 1980's.

The first of these is about a modem that myself and a couple of friends (Max and Bill) designed and built in 1985, called "the Modem".

Bill new someone that worked at AMD, and was able to get us some samples of a new chip, the AM7910, an FSK modem colloquially known as the World Chip. In those days the USA and Europe used their own modem standards, and the AM7910 could speak both. Here's the data sheet:
AM7910PC.zip
(1.75 MiB) Downloaded 35 times
Mostly from the datasheet, we came up with the following hand drawn schematic:
IMG_0241.JPG
IMG_0241.JPG (1.86 MiB) Viewed 701 times
Note the proper isolation of the phone line from the rest of the device. We were a bit paranoid at the time that we would get caught attaching unapproved equipment to the phone line, so tried to do everything properly. We were a bit unsure of some of the logic, so used a 2716 EPROM as a crude form of programmable logic device.

Next, we laid out a single sided PCB. I think we did this using Pineapple PCB. Here's the end result:
IMG_0237.JPG
IMG_0237.JPG (233.66 KiB) Viewed 701 times
For a case, we got hold of some empty floppy drive cases:
IMG_0236.JPG
IMG_0236.JPG (228.49 KiB) Viewed 701 times
On the front panel, there are LEDs for Power, Carrier Detect and Online.
IMG_0231.JPG
IMG_0231.JPG (175.09 KiB) Viewed 701 times
The buttons select the speed (300/300 or 1200/75), the mode (Answer or Originate) and the FSK standard (Bell vs CCITT). The red button on the right manually goes online, but there is a relay that does the same.

Here's a photo of the rear:
IMG_0235.JPG
IMG_0235.JPG (145.34 KiB) Viewed 701 times
You can see the mains power in, a fuse and a power switch. The grey cable connects to the BBC's user port and allows the model to be controlled. The DIN socket (hidden behind the user port cable) connects to the BBC's RS423 port. The small toggle switch allows a speaker to be turned on/off.

For software, we wrote our own modem control software that handled dialling, carrier detect, etc. This was packaged up in a ROM we wrote called Ram Master. You can see the modem control commands here:
IMG_0249.JPG
IMG_0249.JPG (125.22 KiB) Viewed 701 times
For the terminal software, we used Commstar and/or Kermit.

Fast forward to today....

I've spent this afternoon getting this working again. This mostly involved making a new serial cable to replace the one that had gone missing.

Here's a small program to connect to Nostromo BBS:
IMG_0245.JPG
IMG_0245.JPG (128.07 KiB) Viewed 701 times
Once connected, all the lights light up (whoooo!!!) :lol: :lol: :lol:
IMG_0247.JPG
IMG_0247.JPG (162.74 KiB) Viewed 701 times
And finally, on to the BBS:
IMG_0246.JPG
IMG_0246.JPG (152.36 KiB) Viewed 701 times
Anyone know any other BBSs?

Dave

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davidb
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Re: Hoglet's Past Projects #1 - the Modem

Post by davidb » Sun Aug 25, 2013 9:17 pm

Is Arcade BBS still running?

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Re: Hoglet's Past Projects #1 - the Modem

Post by daveejhitchins » Mon Aug 26, 2013 8:49 am

Eat your heart out Pace =D>

Dave H :D
Parts: UM6502CE, GAL22V10D, GAL16V8D, AS6C62256A, TC514400AZ, WD1772, R6522, TMS27C512, AT28C256
Products: ARA II, ARA III, ABR, ATI, AP6, MGC, AP5 . . .
For a price list, contact me at: Retro Hardware AT dave ej hitchins DOT plus DOT com

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Re: Hoglet's Past Projects #1 - the Modem

Post by MartinB » Mon Aug 26, 2013 6:30 pm

Awesome work TC, you are a dark horse aren't you :wink: =D>

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Dave Footitt
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Re: Hoglet's Past Projects #1 - the Modem

Post by Dave Footitt » Mon Aug 26, 2013 8:27 pm

That's ace, looks well professional =D>

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hoglet
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Re: Hoglet's Past Projects #1 - the Modem

Post by hoglet » Tue Aug 27, 2013 6:47 am

Thanks for all the nice comments!!!

I think Past Projects #2 is going to be a bit more of a challenge to resurrect, partly because doing so will require me to climb up a large ash tree we have in the garden. :shock:

Any guesses?

Dave

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Re: Hoglet's Past Projects #1 - the Modem

Post by daveejhitchins » Tue Aug 27, 2013 7:13 am

BBC Tree House :lol:

Dave H :D
Parts: UM6502CE, GAL22V10D, GAL16V8D, AS6C62256A, TC514400AZ, WD1772, R6522, TMS27C512, AT28C256
Products: ARA II, ARA III, ABR, ATI, AP6, MGC, AP5 . . .
For a price list, contact me at: Retro Hardware AT dave ej hitchins DOT plus DOT com

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Re: Hoglet's Past Projects #1 - the Modem

Post by aerworuld » Sun Nov 03, 2013 10:14 am

Nice work sir! As Dave said, there's Arcade (still running) and Nostromo which you e already connected to. As far as i know, these are the only two BBS in the UK still actively accepting dial-in old skool styles.

of course, there are many other BBS out there, but they are telnet-only now :/

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Re: Hoglet's Past Projects #1 - the Modem

Post by jonb » Sun Nov 03, 2013 7:00 pm

Hmmm, nice! You definitely had more fun than be back then.

"Interface 2037 ready for enquiry"

"What's the story, Mother?"

Oh dear.. Alien fan ahoy!

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Re: Hoglet's Past Projects #1 - the Modem

Post by Coeus » Sat May 18, 2019 11:42 pm

hoglet wrote:
Tue Aug 27, 2013 6:47 am
Thanks for all the nice comments!!!

I think Past Projects #2 is going to be a bit more of a challenge to resurrect, partly because doing so will require me to climb up a large ash tree we have in the garden. :shock:

Any guesses?

Dave
A computer to amateur radio interface of some sort?

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hoglet
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Re: Hoglet's Past Projects #1 - the Modem

Post by hoglet » Sun May 19, 2019 6:18 am

Coeus wrote:
Sat May 18, 2019 11:42 pm
A computer to amateur radio interface of some sort?
Indeed:
Hoglet's Past Projects #2 - the RTTY receiver

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tricky
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Re: Hoglet's Past Projects #1 - the Modem

Post by tricky » Sun May 19, 2019 8:08 am

Nice one Hoglet, looks like it could have come from WE (meant as a compliment - just in case).

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