Sunday, 6 January 2013

RPi GPIO Breakout for Cheapskates

I told you in an earlier post how much I admire Adafriut's Pi T-Cobbler breakout for the Raspberry Pi. I got as far as finding a UK reseller who listed them (for more GB Pounds than Adafruit charge in US Dollars) but they're on long-term back order - good thing, given the price! I resorted to my native parsimony...

I soon had a copper pattern laid out for a "straight" version which, although it didn't have the elegance of the Adafruit "T" configuration, was (like the T-Cobbler) only 0.3 inches between pin rows, thereby preserving as much breadboard area as possible.


Unfortunately, the XYL smashed my nice old laboratory thermometer over the holidays - serves me right for leaving it in the kitchen (she says). The thermometer is important in my new photo PCB process (to check the temperature of the photoresist developer), so PCB processing is on hold until the replacement arrives from eBay. Undaunted, I looked around for alternatives...

The junkbox yielded up a scrap of stripboard and I stock single and double row headers, so I quickly collected the key ingredients...


I cut the break in the copper tracks using a dental burr in my pre-historic horizontal milling machine, but I'm sure you could do the same job with a knife (it is between holes, you see - so you can't rely on the usual track cutter / drill). A little judicious soldering (after forceful re-arrangement of the pins in the single row headers to make best use of available length) and you have it...


Here's the new baby on the breadboard (still hosting the LED for my Morse Code GMail Notifier and test buttons for my RPi Keyer)...


All that's needed now is a ribbon cable and some IDC connectors - fortunately, the junkbox came up trumps again, serving up an old IDE disk cable...


However, that cable is bigger than the Pi and the breadboard together, so I broke the habit of a lifetime and dusted off the m0xpd PayPal account to order something more appropriate (£2.99, delivered in moments, from PC Supplies Limited - usual disclaimer)


Now the whole shebang looks a lot neater...


Next I've got to figure how to get the UART to send MIDI to my latest monstrous creation at 31250 baud - the widely touted solution of  suppressing the console UART (in cmdline.txt), getting rid of the getty (in inittab.tcxt) and modifying the UART clock speed with a line in config.txt of the form:

init_uart_clock=2441406 

isn't working for me. In fact, it isn't doing anything - serial is coming out resolutely at 38400 baud.

Any reader who sends a solution ( to shack.nasties "at gee male dot com") will get a prize. A very small prize of zero monetary value and no physical substance - but a prize none the less!

Update: The competition is closed - and I claimed the prize (I'm beginning to regret the "zero monetary value" status). I now have the RPi sending MIDI and controlling my MIDI Tube Screamer - I'll tell you all about it in a later post

 ...-.- de m0xpd

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