4 Mar
2016
4 Mar
'16
12:09 p.m.
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