Monthly Archives: August 2009

Dot Matrix Clock: Order placed

I have finally placed my order for the dot matrix clock. I chose revision 3.5 which had a surface mount crystal instead of the through hole version.

The only problem I have run into so far is that Olimex requires that the payment informatoin be faxed, so I have to use the fax machine at work to fax the order information. Luckily, my dad also works there and if he uses it for personal use there is much less chance of him being punished than me.

I just have to hope that they notice that all my solder side stuff is mirrored as that is the default with Eagle.

Dot Matrix Clock: Down to two candidates

Well, just a short update here. I think I will probably be at home for another month or so, so I am going to go ahead and order the dot matrix clock display board. However, I need to decide between a surface mount crystal or a through hole crystal. I think my post on pretty much sums up my dilemma:

I have two possible versions I have been designing for some time now. Since it is looking like I am going to be home long enough to finish it I guess I should get it fabricated. However, one thing needs to be decided before I order it and that is whether or not I should use a Through-Hole or Surface Mount crystal.

Originally I was going to just use a through hole crystal, but after having a friend of mine look over the board as another set of eyes he pointed out that my crystal traces were over 3in long and had several vias in them. So, we identified a spot where a surface mount crystal could go with no vias and 0.5″ traces. The criteria for fitting in this space was that the crystal had to be no more than 7mm long, 3mm wide, and 1.5mm tall. The obvious problem here is that nothing really fit in that space except for a crystal made by Abracon that is 3.2×2.5×0.7mm. Now the problem is size: is the crystal too small?

My resources: 0.015″ solder, 1/32″ spade tip (on a variable temperature soldering iron), solder wick, and a relatively steady hand (successfully soldered a .4mm pitch 64tqfp by hand without overheating it).
Things I don’t have: A magnifier, reflow oven
Things I don’t have but could get: Heat gun, solder paste

I don’t have enough experience with this sort of thing to answer it myself and I really can’t afford to buy two versions of this board. Is using a crystal this small really worth it?

Well, hopefully I will have that problem solved before the end of the month so I can place my order as soon as Olimex comes out of their summer break (for some reason, Europeans take a month long vacation from work in the summer…how odd…).