Friday, May 11, 2012

CryoBUG PCB Layout Revisited

Without fail there is always something that goes wrong at the last minute, or more specifically something that I overlooked. Well in this case it was the transformer's footprint and pin-out that I totally misrepresented. Apparently I need to do a better job at reading data sheets, because I mistakenly confused the transformer I wanted to use with one of a much lower VA rating, hence a much smaller size. Luckily I held off on having printed circuit boards made until I had all the parts in hand, and had checked them for physical fit against my layout.

So I needed to make room for a bigger transformer. This ended up taking my original 2.5" width to 3", and at the same time it took me out of the running for getting the ExpressPCB Miniboard deal. So here's what the new board layout looks like...

Rev 1.3 PCB Layout  -- Click Image to Enlarge --
I also took the opportunity to clean up some of the trace paths, and to add the Mytek Controls logo to the silkscreen layer. So the final board size is now 3.8" x 3.0". So just for grins, I used the compute board cost feature in the ExpressPCB software and here is what it came up with for production quality board cost.

Qty 2 Boards  = $284.22
Qty 10 boards = $321.94

Wow! That was quite expensive. So next I went to Futurlec's PCB manufacturing page and entered my data. Here is what they showed when calculating the price.

Qty 2 boards   = $  75.70
Qty 10 boards = $134.50
Shipping = $9-14 by Standard Post

So it looks like Futurlec will be making my boards.

Since there were some changes in the transformer pin-outs, and I made some adjustments in the LED drive resistors, including adding a resistor for the external On/Off switch's internal LED back lighting, I updated the schematic to Rev 1.3 as well.

Rev 1.3 Schematic (page 1 of 2)  -- Click Image to Enlarge --

Rev 1.3 Schematic (page 2 of 2)  -- Click Image to Enlarge --

Originally I thought I could purchase the switch I had in mind with a built-in resistor for 12V operation, but as it turns out this would have been a special order, so I opted for the one without the built-in limiting resistors. To accommodate this, a resistor (R19) was added to the board.

I should be ordering boards within the next couple of days.

R600a news

Well my source in England turned out to be a bust. They basically credited my PayPal account with no explanation given as to why the order got aborted. So I am once again searching about for a cheap source of iso-Butane.


Bill St Pierre said...

Seems like there's always one more little detail (like that transformer) just waiting to trip you up on every project. Luckily you caught it when you did.

Michael St. Pierre said...

Yep I remember a board I designed and had fabricated several years ago that had a direct short to +5V. It was a real bit_h to fix, since it was a 4 layer board with inner power planes. Anyway I just sent my file off to be made, so I'll be keeping my fingers crossed that everything is OK at this point.

TPSC said...


How much are you looking for?

Michael St. Pierre said...

I'm looking for about 1lb of R600a (iso-Butane) to continue my charge development work. But even 1/2 a lb would probably be sufficient to zero in on the correct charge blend.

Anonymous said...

It's england

Michael St. Pierre said...

Too bad I don't live in England, because then it would be relatively easy to purchase R600a. Although things are beginning to change over here in the US, with EPA starting to allow it's use as of this year under their SNAP directive. Although it doesn't do me any good until manufacturer's get on the band wagon, and there are enough domestically produced products using R600a, for the local refrigeration suppliers to carry the stuff.

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