2011-04-09

SBC6120 - Power Supply Board

It had been planed for ages, but I never had the time or a technical "consideration" delayed me. I finally decided to just do it (after reading the "cult of done" manifesto), the board with the Laser Toner Transfer and HEMA inkjet photopaper, this was probably the biggest board and with the least detail I've ever done (160x120mm).

The board needed only to fix the connectors, the power switch and a switching power supply. I didn't have much space available on the top side, so I went through my "pile of components" and found a couple of single IC switching power supplies (the National LM2575-5V), I also had a SMD version of it (or so I thought) and some SMD Schottky diodes. The board is also used to mechanically fix the 3.5 inch Harddrive.


The schematic was simple, just the switch, the connectors and the switcher, I added a turn on delay to let everything power up slowly (see the LM2575 datasheet).


The power switch (and the lever) are from C&K, but I had to buy an "old lever" as the new levers are much wider than what I could "afford" in terms of space on the front panel (there's no bezel for this older one though).
For the PCB I had some problems, but mostly mechanical. You can only see them when I show the pictures of the completed unit. I had to fit a 10mm inductor in a 10mm space and a 3.5 inch harddrive in 3.5inch (minus 1mm space, there's a screw on the harddrive I had to remove, otherwise the top would not close.

This is probably the only reason why I'll do boards at home, it must be a big board (>160mmx100mm), few tracks and single side, if it misses one of the tests, I'll go for a Fab. board.
After assembly... it didn't work... A quick trouble shooting revealed the cause... poor eyesight.
I had a LM2595S not the original LM2795 with which I drew the schematic and PCB. The pinout is very different. Then I found out I had no LM2975 SMD version. I had to improvise, a through hole package with bent leads and plenty of flux later...


After that mishap, I mounted everything back up and it worked. I formatted the drive and downloaded a disk image and now my SBC6120 boots!



It was done in two weeks! I'll try to keep this "cult of done" thing going on (but some of the tasks need to be broken in more than a couple of weekends).

2 comments:

Roger said...

Excellent - well done on the 'cult of done' front.
I've been doing quite a bit of research on how to focus better during a work day; setting up things like RescueTime and Pomodairo and listening to lots of Merlin Mann.
Loading heaps of podcasts (including Merlin) on mp3 player for long walks (getting colder down here now though :-/ ).
Someone said to me the other week, "the more you do the more you feel like doing" ... so I'm doing some little things like assembling an RS232 to TTL shifter board kit. Trivial, but therapeutic and satisfying :)
Keep up the good work!

J Silva said...

Hi again Roger!
I had to change, to much planning and not enough doing... I've also started using the Pomodoro technique during work.. but I need to keep "reminding myself" of doing it.. But I firmly belive that it works! I have a related project (a pomodoro timer). more on it later.
JSilva