Sunday, December 7, 2014

Power supply and wiring work on SAC Interface Box

Working at a conference in Las Vegas this week - non stop giving talks, meeting with attendees and other activities from breakfast to dinner time. I was only able to snatch one or two tiny intervals when I had breaks and needed the change of pace. Not much was done but now that I am back home, I could pick up the pace. I didn't post this until Sunday morning but it represents the day's work yesterday.


I began setting up the Python environment and getting things in order to code the PC side software for the interface link. This includes the ctypes library that helps with calls to C based libraries such as the Adept2 from Digilent.

My naive assignment of signals to pins on the breakout board assumed that each pair of FPGA inputs (e.g. LA01P and LA01N) were assigned sequentially, beginning with LA00P at pin 1 and ending with LA19N at pin 40. When I looked closer, that wasn't a valid assumption. Instead, the pairs are assigned in the pattern LA00P at 1 and LA00N at 3. LA10P is at 2 and LA10N is at 4. In other words, the pairs are not wired vertically to each column of the two-row connector. The bottom row has the pairs assigned left to right, then the top row continues with the next ten pairs, assigned left to right.

My SAC interface cards are wired into the connectors in the pattern I expected, so that a register might be assigned to pins 1 through 16 sequentially. I worked out all the FPGA signals that correspond to the breakout board pins, which allowed me to map the fpga inputs to the proper logical signals in the hop-around pattern the board actually takes. It was time consuming but now all is correct as far as I can tell.

Twisted pairs to interface board stack from right, single ended lines to FPGA board at left.
All the wiring of the interfaces to the fpga board connectors is done and I am finishing the insulation of the 'joins' where I soldered the stranded wire that fits crimp connector pins to the solid wire that is easy to insert into PCB board holes. I used heat shrink and my hot air rework gun to insulate all those ends, then wrapped groups together with electrical tape.

Heat shrink insulation of solder joints on wiring to the connector
An ATX power supply fits into the case and serves as a good source of 12V, 5V and 3.3V power for my unit. I used a 24VAC relay for the 'power' switch of the supply, which will connect to the 24VAC power that is used in the 1130 system to power up all peripherals. I still have to add filter capacitors and a voltage regulator to get the 5V and 3.3V sources to the exact levels of 5V and 3V that I need. The FPGA board takes a 12VDC input, directly from the ATX supply so it will come up as the 1130 itself is turned on.

ATX power supply in place and 24VAC relay loose on top for remote power-on by 1130


I spent a bit of time cleaning and inspecting the parts from the feed clutch that I had disassembled before my trips, in anticipation of re-installation, lubrication and adjustment. I didn't begin the assembly itself today but expect to get to this (plus finish the 1053 console printer repair) soon. 

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