KB6NU's Ham Radio Blog

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Can you do DSP with an Arduino?

Posted: 12 May 2017 11:44 AM PDT
http://feedproxy.google.com/~r/kb6nu...m_medium=email


Last fall, I ran across the Kickstarter for the Teensy 3.5 and 3.6. The
designer, Paul Stoffregen, bills his Teensies as powerful
microcontrollersÂ*for making awesome DIY electronic projects. The Teensy 3.5
uses a 120 MHz ARM Cortext M-4 processor with a floating-point unit. The
Teensy 3.6 has a 180 MHz processor. And, they are Arduino compatible.
The Teensy 3.5 Arduino-compatible microcontroller features a 120 MHz ARM
Cortex M-4 processor with a floating point unit. The Teensy 3.6 uses a 180
MHz processor.

Hmmmm, I thought to myself, I bet these processors could do some digital
signal processing. I got really interested when I read about theÂ*Teensy
Audio Library, which is a toolkit of dozens of audio processing components.

So, I Â*joined the Kickstarter, and in due course a Teensy 3.5 arrived in my
mailbox. Of course, I havent yet done anything with it.

Well, yesterday, my friend, Quentin, KD8IPF, sent me an e-mail posted to
the 817ND mailing list. It was posted by Gareth, GI1MIC, and includes a
couple of links to an open-source project that uses an earlier version of
the Teensy to implement an audio DSP add-in for the FT-817. The links
include:

Code and instructions
A video showing the Teensy DSP in action


Gareth notes, The project is easily modified to run on other rigs or could
be fitted inside an amplified speaker. The latter is what I had in mind.

On the code and instructions page, Gareth links to a tool called TFilter.
The web page describes this tool as a web application that generates linear
phase, optimal, equal ripple finite impulse response digital filters. It
uses a pure javascript implementation of theÂ*Parks–McClellan filter design
algorithm. This tool generates the coefficients used by the Teensy program.

I havent really looked at the code yet, but Gareths program will switch
between a CW filter, a SSB filter, and a third type that I couldnt make out
from the video. In Gareths application, the Teensy is embedded into the
FT-817, and somehow he is able to use one of the radios controls to switch
between the different filter types.

Another thing about Gareths project is that it uses a Teensy 3.2. The
Teensy 3.2 uses a 72 MHz ARM processor, and apparently, thats quite enough
power for audio DSP. The Teensy 3.6 costs $30, while the Teensy 3.2 costs
only $20.

I always thought that Id build mine into a speaker. Not only that, I would
like to have a PC application, somewhat like TFilter, that would allow a
user to build his own filter on the fly. The program would have to
calculate the coefficients on the fly and then download them to the filter.

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