Beyond what others have mentioned like the TNC-Pi (nice kit), using a $7 USB soundcard and Direwolf will provide superior decodes.
Yes, I wonder why on earth they use a hardware AFSK modem chip in that design... I can see a place for an adapter board that provides PTT keying, possibly isolated audio interface, etc for the Pi, but it should always just do A/D and D/A conversion of the audio and leave the processing to software. That works so much better, and it enables the development of alternative modem designs without having to change the hardware every time.
Rob
Hello Everyone,
Yes, I wonder why on earth they use a hardware AFSK modem chip in that design...
Well, I see the desire for something simple, plug & play, power efficient, etc. and the TNC-Pi delivers there. The strengths there are also it's weakness. Direwolf for example, gives a LOT more options and uses various approaches to dig out the proper signal. It can even repair bad packets but at that point, it's only solving to make the CRC valid though the resulting packet could be corrupt.
I can see a place for an adapter board that provides PTT keying, possibly isolated audio interface, etc for the Pi, but it should always just do A/D and D/A conversion of the audio and leave the processing to software. That works so much better, and it enables the development of alternative modem designs without having to change the hardware every time.
Yes.. and it's DONE! James N7SET created a PCB based upon the circuit design in the Direwolf documentation and it's available for one-off shipments via OshPark:
https://github.com/jaymzx/RPi-WD-Packet-Interface
You can take this board and either hand wire it up to an Rpi/BBB/whatever or my approach has been to mate it with a Rpi proto HAT like:
https://www.adafruit.com/products/2310
and you have a powerful yet plug and play HW/SW setup. I also know that James was working on a future version of that board that was to incorporate isolation transformers (that can be bypassed for 9600 needs) and opto couplers aka like the EasyDigi kit on Ebay. This would then be natively supported on a Rpi B+ compatible PCB. I need to reach out to him and see how that project is coming.
--David KI6ZHD
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David Ranch -
Rob Janssen