[arm-allstar] GPIO vs Nano

[George Csahanin]

Barry, I see the thought process, the 'duino is cheap. After reading the explanation a while ago that also 'sprains that this can be used as a gpio expansion for other than Pi the light went on. Got it. 

Is the 'duino code "out there"? Pretty useful devices. I evolved a nano into a replacement head for the Micom-2 HF radio. I like the I/O abilities...

GeorgeC
W2DB 2360

George Csahanin
Media General
Sent from my iPhone

> On Dec 6, 2016, at 4:56 PM, Barry Buelow via arm-allstar <arm-allstar at hamvoip.org> wrote:
> 
> All,
> 
> I originally built a pcb that plugs into the GPIO of the RPi. It had room for 2x FOBs (minus plastic cases) and buffers for PTT-COS. I have experience with complex board design (avionics) and expected some coupling from the RPi to the board, but it was significantly higher than I expected. The audio always had "worms" and it was quite difficult to knock down the spikes on the +5 and +3.3. The short answer is that the IO board was too close and there was no simple way to get more isolation. It was also clear that if there were some undesirable event on the radio, the path to Gnd was via the RPi. An aside comment for now: building a system with several floating ps is a really bad idea.
> 
> Over the past few months, I've shown Dave and Doug my work and received comments. The NanoDB is not a bullet proof interface. Doug always argues for cheap :-), but he wants the features of a more expensive unit.  The NanoDB is rather minimalist in design. I had a 74HC14 buffer between the inputs (COS, CTC) and the Nano, but took it out. The amount of protection it offered was inadequate if there were a big event (as was re-enforced at an IEEE EMI class a few months ago). The 74HC14, with jumpers, also allowed the IO to invert signals to have LEDs indicate the correct state regardless of COS=1 or COS=0 from the radio. I still like that idea, but it can be accomplished in the Nano Sw.
> 
> What drives my designs is the desire to have no external ugly blight of wires and components necessary in normal installs.  Why would anyone want a design that requires external 2N2222 + bias resistors hanging in midair off of a DB25?  My goal was to have the NanoDB work for 90% of the simple nodes. It allows use of the potted FOB to build a cheap system.  I'd be very interested to hear about cases where it did NOT work as a future rev might address some issues.
> 
> I have also contemplated a more elaborate mechanical design which accommodates IO for 2 radios, 2 FOBs, and integrates into a nice extruded metal case with room for a pair of DB-9s on the rear. Think bigger $.  Dave suggested an integrated USB HUB. Those are fine pitch parts which exclude home bench soldering and small quantity builds are more expensive.  Maybe someday.
> 
> I think the NanoDB will be a contribution to Allstar, which was my original intent.
> 
> Barry w0iy
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