DiscFerret update: PCB done!

Philip Pemberton classiccmp at philpem.me.uk
Fri Sep 3 21:08:16 CDT 2010

Hi guys,

I've just (within the last few minutes) finished the "first cut" board 
layout for the DiscFerret. It's a 160x100mm Eurocard, with all the 
"inputs" (power and USB) on the back panel, and all the disc-drive 
interfacing stuff (power and I/O) on the front. Truth be told, it's not 
much different to the prototype schematic I posted to the list earlier 
this year...

The 40-pin disc I/O connector carries a standard 17-line ("34-pin") 
Shugart disc interface with all lines wired, four high-speed 5V TTL 
"user I/O" lines, +5V (low current) and ground. The state of the DENSITY 
pin (pin 2) can be driven as an open-collector output, or used as an 
input (depending on the type of drive you're using).

There's an external "power output" connector for the disc drive. This is 
a dual-row 4-pin AMP Micro Mate-n-Lok (P/N 3-794618-4, mating connector 
794617-4 with 794610-1 contacts) which carries +12V, +5V and two 
grounds. Current-handling capacity is about 1.5A per channel, so plenty 
for most PC-style drives. There are no cop-outs here -- you can pull 
1.5A from the 12V bus, and 1.5A from the 5V bus *at the same time* 
without any adverse effects.

I wanted to use the standard Molex floppy drive power socket, but Molex 
only seem to make one PCB-mount variant, which is the "input" socket 
(which has a recessed body, but contains male pins -- go figure)...

There are also three status LEDs -- Power, FPGA Status and PIC Status. 
The first is always on when the +3.3V regulator is running, the latter 
two are controlled by their respective devices. A plastic light-pipe 
redirects the light from these LEDs to the front panel. Simples!

For the curious...
   Schematic:    http://www.discferret.com/temp/discferret_sch.pdf
   PCB layout:
     Checkplot:   http://www.discferret.com/temp/discferret_main_chk.pdf
     Top copper:  http://www.discferret.com/temp/discferret_main_top.pdf
     Bot copper:  http://www.discferret.com/temp/discferret_main_bot.pdf
     Top overlay: http://www.discferret.com/temp/discferret_main_tov.pdf

   EAGLE project files: http://www.discferret.com/temp/eagle/
     (you'll need all the files in this directory)

Next step is to do a full design review (i.e. print the board and 
schematic out REALLY BIG and go over them with a loupe), create a 
Quartus constraints file and test-synthesize the FPGA microcode.

But first... it's 3AM and I'm tired. Sleep time!  zzzzzz....

classiccmp at philpem.me.uk

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