It’s not hard to demodulate the audio in software with an input capture timer on a microcontroller, Arduino, etc.  I’m not familiar enough with the pi hardware to know if it can do the same thing or not. Here are two devices I’ve made that decode FSK audio using software:

  https://deramp.com/model15_interface.html
  https://altairclone.com/cassette.html

If you want to start with either of these pieces of hardware, the Altair cassette interface board would be the easiest to connect directly to gpio pins on a pi. You’d have to write software to monitor the gpio data pin and do a “reverse bit-bang” to receive the 45.5 baud data stream into 5-bit baudot. That could then easily be converted to ASCII and sent to your ASR 33 (assuming you have an RS-232 adapter for your 33).

If your ASR 33 is still connected by current loop, then it might be easier to update firmware in the model 15 interface board to convert the FSK it receives to 110 baud ASCII and drive the 33 directly.

Mike D

On Oct 6, 2024, at 2:18 AM, Rob Jarratt via GreenKeys <[email protected]> wrote:

Hello,

Dave was asking this on my behalf, probably unaware that I am on this list too.

I have seen mention of ITTY Autostart etc and wondered about receiving all this on my ASR 33.

My thought was to see if I could set up a Raspberry Pi to receive the audio signal over the internet, translate that to ASCII and then send it to my ASR33. I already have the means to connect my ASR33 from software running on a Raspberry PI or a PC via reverse Telnet. The bit I am missing is what software (if any) there might be that I could run on a Raspberry Pi, or Windows that runs in the background (no GUI) to decode the ITTY audio signal. I am a software developer though, so I guess if such a thing doesn't exist then perhaps I can modify the MMTTY code that is published on GitHub.

Any pointers would be welcome.

Thanks

Rob

-----Original Message-----
From: [email protected] <greenkeys-
[email protected]> On Behalf Of Jeffrey Golas
Sent: 06 October 2024 05:30
To: David Wade <[email protected]>
Cc: Mailing List Green Keys <[email protected]>
Subject: Re: [GreenKeys] ITTY to real Teletype

Normally the ITTY service is fed to a piece of hardware called a terminal unit
(think modem). The service is streaming as RTTY which is normally sent over
amateur radio.


Jeff

On Oct 5, 2024, at 5:34 PM, David Wade <[email protected]> wrote:

I know there have been several USB to TTY boards produced, but what
software would you use to drive one of these from itty?

Dave

G4UGM

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