[hpsdr] Lionheart board

[Lyle Johnson]

> The latest block diagram of the proposed Lionheart is at
> 
> http://www.hamsdr.com/dnld.aspx?id=124

Note that this is a GIF file, so you must append the .gif file type to 
it for Windoze, if you are of that persuasion (or have no other 
practical choice!).

> Based on the work that we have done to date with the Xylo,  the changes I
> would make would be to add  PTT, dot and dash inputs on the board edge
> rather than bringing them onto the board via the Atlas bus.

Alternately, these couple be mapped to the "External Control In" buffer. 
  Might want to consider a 10K pull up on each of these 8 pins, to 
+3.3V.  Might also want to use a 74LCX541 or similar series buffer on 
these lines so the inputs will be 5V tolerant.

The GPS timing input should have some sort of signal conditioning on it, 
even though this will likely add a tiny amount of jitter.  I get nervous 
thinking about a "bare" pin from the FPGA fgoing to the outside world 
where ESD and other delights lie in wait...

Finally, please consider including protection on the USB connector, 
something like an ON SMS05T1 (Digikey SMS05T1OSCT-ND).

73,

Lyle KK7P


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