Subj : Re: Using AX.25 w/older h
To   : Damom A. Getsman
From : Ed Vance
Date : Tue Mar 03 2015 12:41 am

Damon,

The 555 A.F.S.K. Oscillitor circuit I connected to the Netronics ASCII/
Video board I found in the May 1977 edition of QST magazine on page48 .
The circuit also uses three 2N2222 Transistors and other parts.

The circuit I used for a RTTY Demodulator I 'borrowed' from the
Microcraft(R) RTTY Reader article in the November 1979 issue of Popular
Electronics magazine.
It had three I.C.'s, two 1458 and a LM301, two 2N2222 (or 2N3904)
Transistors and other parts.
I also had a 7414 I.C. which I used two of the NOT sections in it to
either let the signal from the Demodulator go as is to the Netronics
Board, OR to Invert the signal if I needed to.

Those two circuits I call my 'RTTY Modem', and I used two I.C.'s, a
74LS04 and a 74LS00 plus some switches to interface it to the Netronics
board.

The ASCII/Video board had a MK3870 F8 Microprocessor on it.

I visited another Ham who was showing me his CW Video Keyboard that
he bought which could Send and Receive CW up to 60 WPM.

I asked him if I could see the schematic for it to see what made it
work and noticed it used the same Microprocessor (uP) that was in the
Netronics ASCII/Video circuit.

On his schematic I saw a Reset Switch was connected to the uP, so I
copied that portion of the schematic, so I could add it to my RTTY
set up.

I wanted that Reset Switch circuit really bad because the Power Supply
I bought from Netronics to run it, didn't have a Power Switch, and I
had to unplug the power supply whenever I wanted to change to a
different speed.

I had two SPST Toggle Switches on the back of the Keyboard case which
I used to change the Baudot or ASCII speeds.
They were wired up to two sets of Jumper terminals on the ASCII/Video
board because I didn't want to solder the jumpers for only one speed
and then have to open the case up to Unsolder and Solder those Jumpers
for a different speed/mode.

I usually used 60 WPM - 45.45 Baudot but I also used 100 WPM - 74.2
Baudot and 110 Baud ASCII, so I added the 'borrowed'Reset Switch
circuit to my setup.

The first time I pressed the Reset Button to change to a different
speed, I ZAPPED (Fried) the MK3870 uP and had to order another one
from Netronics. Go ahead and laugh, I don't care.

While I was waiting for the new uP to arrive in the mail I removed
the Open Circuit SPST Pushbutton Switch and put a Closed Circuit SPST
Pushbutton Switch in.

I used that switch to interrupt the power coming from the Power Supply
line before it went to the circuit boards inside the Keyboard cabinet.
That Modification did what I was wanting to do when I wanted to change
to another Speed or Mode (Baudot or ASCII).

I was able to use 3 out of the 4 available speeds the Netronics ASCII/
Video board was designed for by flipping the Switches that were wired
to the two Jumper Connections on the board.

I never was able to Receive or Make a contact with 300 Baud ASCII, but
I am satisfied that I could use 3 of the speeds for my Ham Radio hobby.
73

P.S. The main reason I thought to tell You all this was to show You that
I am not 'The Man' who knows everything when it comes to changing the
way a circuit is designed.

Usually I will talk to someone before I change things to see what they
think of my idea, I didn't that time, and it cost me, iirc $37.00 USD
extra for the 2nd uP.

I try helping and saying what I know or 'think' when I hear of some
need that I believe I can be of help on.
Just don't take every word of mine as GOSPEL, I was called a LID by
the Hams I knew in High School BEFORE I even got my Novice License.

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