Dr Jefyll wrote:
backspace119 wrote:
The smaller I make this, the cheaper it gets
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Can you do this? And there are other opportunities. As you say, it's worth going over it again. Really, there's quite a lot of unpopulated area.
Have fun!
That's an amazing idea right there, I've been spending time cleaning up some bad traces, got the via count down from ~750 to ~650, moving those might help some too (although might put some feet over vias, but who cares, needs re routing anyway). This, combined with making the clocks smaller (dip 8 instead of dip 14) I can probably save some good board space.
I may go with what Garth was suggesting and throw some chips underneath the bigger chips sockets, although that would mean not putting the smaller chips in sockets (unless they were really short). Honestly, that will be a last resort.
I don't remember if I mentioned this, but OSHPark (I've gotten boards from them before, and they're good quality) quoted me about $420 to make this. That's for 3 boards, but that's still over $100 a board! Seeed I have not actually done a quote with (haven't uploaded the file) but they have a configurator where you can put in all the specs for your board, and they were quoting me about $150 for 10 boards!
I don't think OSHPark's quality is worth paying nearly 10x as much per board, and the turn around times (minus the fact that seeed is closed due to the chinese lunar new year until the 11th) are about the same from what I've seen. Plus, OSHPark only sells purple boards, and for this project, I'd like the "old fashioned" green a lot more. (seed even lets you get them in other colors, like black, blue, etc).
OSHPark, and some other american board makers with them, are good companies, but they probably need to refine their process to be able to compete with places like Seeed, because I don't see the point in paying all that extra money.
Chromatix wrote:
About 74F series logic: it's pretty fast, yes, but it's *very* power hungry, on the order of 35mW per simple logic chip. It has typical TTL input levels, input loads (this is *not* a high-impedance input, due to the bipolar transistors involved) and fanout restrictions. It's also no longer being manufactured.
If you need fast logic, I recommend 74AHC series, switching to 74AC or 74HC for specific devices not available in that series. A quick pricing comparison suggests there's not much difference.
I only remember seeing the price difference on one chip, the 74318, and the AC (maybe AHC, pretty sure it was AC though) version was >$2, while the F was $0.60. For a chip that I need 3 of, the cheaper option (that was basically as fast) looked better, but knowing this, I'll stay far away from the F series.