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using the 82168A 300 baud modem!
07-10-2020, 09:05 PM (This post was last modified: 07-10-2020 09:08 PM by vassilisprevelakis.)
Post: #1
using the 82168A 300 baud modem!
Hi all,

It all started when I wanted to charge the 2nd battery pack of my HP-75C. So I dug up my 82168A HP-IL modem that uses the same battery pack with the bonus that it uses the more popular 82059 charger (same as the one for HP-75C and most HP-IL equipment).

When the pack was charged I was ready to store the 82168A back in its hiding place when my 11-year old son showed up and asked what that thing was.

So I started explaining but I realized I needed a telephone handset to show how you used the modem.

Where do I find an 80s handset in my flat in Germany?

Pause, and then AHA! I remembered that at a conference some years ago I was given a toy that looked like an 80s handset, but it plugged into the audio/mic socket of my laptop so that I could do my Skype calls with what looked like a legacy phone. Cute, but useless until today! I dug it up and wow it fits like a glove to the 82168A.

With the charged battery pack as soon as I connected my HP-41 with the HP-IL interface the 82168A came up (the pale red flag flipped into a bright red flag). Now how to get the “Carrier Detect” flag to turn on (actually show us its darker green side).

I tried whistling and although back in the 80s I could get a fax to respond, I have lost the gift, and the 82168A ignored me.

So the demo ended poorly.

But getting the 82168A to work, kept bugging me but there was nowhere I could find another modem in my flat. Even my 12 year old Mac does not have a built-in modem.

So deadlock until I got another idea. Why not use the audio output of my laptop to simulate a 300 baud modem. Clearly it has the computing power to emit the chirps at the correct rate.

So I looked around and found the minimodem program written by Kamal Mostafa which did exactly what I wanted.

There is even a youtube video showing how to use the minimodem to connect to a BBS. Wow!

Of course minimodem wouldn’t work on my Mac, so I used one of my Raspberry PIs to install and run minimodem, and it WORKED!
I can type stuff on my Pi terminal window and it gets displayed on the HP-71B running a 5-line program.

As a bonus(?) the whole thing is battery powered!


In the picture you can see that the 82168A is powered up and is detecting the carrier signal. I then typed a short message (blind, since there is no display connected to the Pi) and it showed up on the HP-71B screen.

The HP-71B program is as follows:

10 DIM A$[80]
40 DISP A$
50 GOTO 30

(It only allows data from the PI to be displayed on the HP-71B as I haven't managed to get minimodem to receive data)

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07-12-2020, 01:29 PM
Post: #2
RE: using the 82168A 300 baud modem!
Somethings *must* be done. This is one of them :-)

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07-12-2020, 01:48 PM
Post: #3
RE: using the 82168A 300 baud modem!
Wow! Lots of creativity here, great story, thanks! Smile

I was more lazy, I took the easy route. I bought :
  • 2 x US Robotics modem
  • 2 x 82168A HP-IL modem
  • 2 x old dial tone phone with 82168A compatible handset
  • 1 x phone line simulator that support pulse and dial tones, has 4 lines and is soft configurable.
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