Quote from comp.sys.sinclair:
Here is an SMS-sender application for ZX81:
http://www.youtube.com/watch?v=qfdSRsDwEYo
Note that the Z80-chip in the movie is not the same as in ZX81, since
ZX81 uses a Z80 in 40 pin DIP (DIL).
I typed in the program ZX81 SMS SENDER from screen:
10 CLS
20 PRINT "POWERED BY WDS GLOBAL"
30 PRINT "ZX81 SMS SENDER"
40 PRINT "ENTER MOBILE NUMBER"
50 INPUT N$
60 PRINT "ENTER MESSAGE"
70 INPUT M$
80 PRINT "CM"
90 PRINT "D:N";N$
100 PRINT "CM"
110 PRINT "D:M";M$
120 SAVE "PROG"
130 GOTO 10
Here is an explanation from the application maker:
'But, by way of an overview, ZX81 -> SAVE file -> laptop converting
beeps back to data -> WDS SMS Sender -> Nordic EMG -> SMSC. We have some
infrastructure here already (an SMSC link), although you could use
equally use a mobile dongle. To? be honest, the ZX81 doesn't play the
biggest part in this!
The data was sent by audio (using the SAVE command on the ZX81) to a
laptop that converted the audio back to data and then forwarded the data
to WDSGlobal's? SMS Sender, which uses Nordic Messaging's EMG to connect
to the SMSC. It's a light hearted project with little point, but it does
really work!
The program inputs some data, PRINTs it to the screen (with prefixes
like "M:" for mobile number) and calls SAVE which outputs it's entire 1K
memory as audio.
zx81get is a tiny c-language program bundled with the "z81" emulator
that converts audio data to characters.? We hacked it to write data to
STDOUT. It reads from /dev/dsp on Linux with a low baud rate (to reduce
possibly of noise). The beeps are short or long, representing 0 & 1.
A ruby script parses this data and calls the SMS Sender.'
I don't think the entire 1 KB memory is saved to tape -- only the used part.
I think they use the fact that the screen is saved to tape (in this case
directly to line-in of the laptop) and then they extract mobile number
and message from the display file. They could also extract the data from
the variables since they are also output to the MIC-connector.