🚀 go-pugleaf

then@vipunen.hut.fi (Tomi  H Engdahl) writes:

> In article <6LRgPB4w165w@bluemoon.rn.com> gerry@bluemoon.rn.com (Gerard M. Fo
> 
> >   Since it seemed busted anyway, I just now pried it open.
> >I have not finished tracing the schematic diagram of it,
> >but believe it or not, it containes the following parts,
> >and no more:  1 Dual Op-Amp  5 resistors  4 diodes 4
> >capacitors! (Sorry for the spelling of "contains" up
> >there).  There's magic in electronics!
> 
> The magic is mainly in software, because most decoding of the
> fax signal is done in software. That's what I think.  I have seen 
> a shareware program called Hamcomm, which can send and decode 
> morse, rtty etc. signals. The circuit needed for decoding contains one
> Op-amp and some passive components. The circuit filters the incoming
> signal and converts it to square wave, which is send to one of the input pins
> in the serial port. Every time the state in that input changes, UART
> generates an interrupt. The software measeres time between interrupts
> and so determines the signal frequency. When the program is used for sending,
> the PC speaker ouput is connected (via passive low-pass filter) toi the
> transmitter. Quite a hack.
> I think that the fax device you mentioned works in the quite same way.
> 
>  
> --
> 
> Tomi.Engdahl@hut.fi            "Don't force it; get a larger hammer"
> then@vipunen.hut.fi                        

   The op-amp was a Motorola LM358N.  I replaced it with a
Radio Shack Cat.No.276-038, price $0.99, and the AEA-FAX
seems to work again.
    It looks to me as if the AEA-FAX gets its power from
RS232C line 20 (DTR) when that is made positive.  It seems
that the device is reset and interrogated on line 4 (RTS)
and that the brightness level is proportional to the time
that elapses until line 6 (DSR) changes state.  If any
software geniuses have good ideas on how to program to
make this work, I would be very happy to hear from them.
     For VGA display, the device and software must perform
the conversion to a gray level 480 times for each FAX
drum revolution.  The FAX drums turn at 1, 2 or 4 times
per second.

 This is from
     gerry@bluemoon.rn.com
who doesn't have his (or her) own obnoxious signature yet