assembled and working :)

The Logic Pirate is a medium speed, low-cost logic analyzer with a USB interface. It can capture up to 256K samples at 20MHz (80MHz with overclock), and is compatible with SUMP logic analyzer client. Get one for $30 at Seeed Studio. Logic Shrimp support available here.

assembled and working :)

Postby arhi » Tue May 31, 2011 3:49 pm

Finally got few hours free to assemble logic shrimp (got the pcb via mail from Ian some time ago)...

Two major issues with it ..

1. buffer, the one I have (LVC573A) is narrow and wide package so pins can't touch both sides :( so I have to add some wires or to make some solder bridges hence it does not look very nice

2. I had no 20MHz smd oscillators so I had to order some, I ended up with CTZ CTX750FBC a citizen oscillator, 3v3 power, 100ppm, same pinout as the schematic imho..

After I assembled the board, powered it on, there's no clock going from the output of the oscillator. Vdd measures 3v3 but scope show output of the oscillator is 0V :(

Oscillator is properly soldered I'm pretty sure (check pics), after it didn't work I heated it up with reflow gun and solder reflowed nicely, the oscillator was held with solder surface tension, cooled down .. same thing ..

I don't have time to play with it any more today but if anyone have any ideas where to go from here, lemme know. (If not I'll remove the oscillator in few days when I get another hour to play with it and try to use "big" 20MHz oscillator instead
Attachments
2011-05-31-223125.jpg
pin on the pic where clock from oscillator connects (400x)
2011-05-31-222914.jpg
20x
2011-05-31-222954.jpg
20x
2011-05-31-223239.jpg
20x
Last edited by arhi on Sat Jun 04, 2011 6:01 pm, edited 1 time in total.
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Re: assembled but .. for some reason oscillator ain't oscila

Postby ian » Wed Jun 01, 2011 1:18 am

Very clean soldering job. I'll try to think of some suggestions, but nothing comes to mind immediately. If you need another OSC let me know and I will mail it.
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Re: assembled but .. for some reason oscillator ain't oscila

Postby arhi » Wed Jun 01, 2011 5:47 am

ian wrote:Very clean soldering job.


Thanks :D it is done with some helping hand of that home made flux I use :D

ian wrote:If you need another OSC let me know and I will mail it.


If this one is for whatever reason dead I will have to order a new one as noone locally has them :( .. but I never seen them die "just like that" so I hope it is something else.. Thanks in advance I will let you know how the testing goes but it will have to wait few days
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Re: assembled but .. for some reason oscillator ain't oscila

Postby arhi » Sat Jun 04, 2011 10:44 am

The problem was under the oscillator ... the pcb trace connected to ground.

I cut the problem with a knife and it finally works :D
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2011-06-04-171857.jpg
trace connecting to ground
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Re: assembled and working :)

Postby ian » Sun Jun 05, 2011 3:16 am

Sorry about that. Does your board have a red mark on the side (etest indicator)?

I have started to order 100% etest now that we're shipping so many free boards. It wasn't a problem before, but it's cropping up a lot lately.

Thanks for posting a picture of the assembled board. Another free PCB coupon is on the way.
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Re: assembled and working :)

Postby arhi » Sun Jun 05, 2011 7:36 am

No worries, it was actually fun to debug :) and no, there's no red marking on the side.

I had a young friend here as he wanted to learn something so I used the "debugging of the LogicShrimp" to show him few things ...

As the output of the osc was not working I first suspected at this 74LVC1G125 so I removed it, it was easiest to remove and return and it was the only part that I believed could be dead and preventing oscillator output from working... After I removed it there were no changes so I moved forward and removed the oscillator completely and attached external 20MHz oscillator (DIP14 you can see it on the pic on my blog) and because I only had 5V one I attached 3 zenners to the output... This didn't solve the problem ... As at that moment I knew I'm sending proper clock to the pic and I knew pic was ok (I reprogrammed it with pickit) I measured trace to ground and voila - it was 0R :D ... then I turned on the VEHO and inspected the trace, cleaned it, returned both 74LVC1G125 and oscillator, powered the thing up and voila :D
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