On Fri, Jan 21, 2011 at 08:51:40AM -0800, Kirk Wallace wrote: > I was trying to use an ATmega because they are 5V chips, but I kept > running into a problem of having the different functions I wanted being > on the same pins. The Xmegas seem to have less pin function sharing.
Plus on-chip hardware quadrature decoders, and on-chip hardware routing of I/O signals to counters, etc. As well as higher cpu speed. They are good chips to master, I think. > I am thinking the first batch of boards should have just the parallel > port interface, power supplies and other essentials to get the uC to > run, then break out the rest of the pins, so peripheral development > could continue. The more pins available would allow for more flexibility > in how the uC could be used. If a header is used there, then IDC connectors would allow peripheral boards to be easily swapped. > I would also like to follow best or better design practices. So I will > need those that know better, to provide guidance. To that end, I also > tend to copy other designs that are common for an application. The 10 years I spent designing uP-based digital hardware have been followed by 20 years of embedded software hacking, with only the occasional hardware design, but I'll cheerfully throw in suggestions, FWIW. > So far, I have only looked at this chip: > http://focus.ti.com/lit/ds/symlink/sn74lvc4245a.pdf That's just the ticket for the data path. Another, permanently enabled could serve for control lines in one direction, if it saves enough discrete components. > but currently, I see that understanding the EPP software as my next > goal. I have an ATmega setup that I can use to get an EPP component > sorted out, then I can move this to the Xmega. Sounds good. The code's portable, bar some initialisation and pin names, I expect. (Haven't used an xmega yet.) > A few years back (maybe more) I had Sparkfun make some boards for me. > The price was very good, but I had to wait a few weeks for them to fill > a panel, then send the job to China, have the board house find a space > in their normal production schedule, then ship the panel to SF. SF would > then break the panel out and ship. It seemed to be the best deal going > at the time, but I guess hobby fab has come a long way since then? I just hand-solder SMD boards, keeping to SOIC and TQFP packages with not too many pins. TQFP44 was much quicker to hand solder than old-fashioned DIL, the first time I tried it. Just syringe a stripe of flux along each row of pads, plonk the IC down and align by eye, tack two diagonally opposite corner pins to hold the IC, load the hollow in the special tip with enough solder, then wipe along the row of pins, thus soldering 11 pins in 1.5 seconds. (That wipe speed works for me.) SMD discretes are slightly fiddly, but OK in 805 size, I find. (1206 is easier, but I hate wasting the space.) SOT23 transistors are a bit awkward, so I prefer an array if there are several in the design, and the layout can tolerate it. > By the way, I tend to prefer GEDA for schematic and board layout. I > had a hell of a time making new components in Eagle, which I find easy > in GEDA. On the other hand, GEDA has very few pre-made components so > one ends up making a lot more of them. Ah, that's understandable. (I've persisted, and have made a number of new Eagle components, including micros. The only thing which still gives me trouble is allowing connection to either the lead or the tab, where e.g. a transistor's collector or drain is on both.) I noticed the IR2130 on the wiki page. I hadn't seen it before. The PLCC44 package would be easy to lay out, with the 3 high-side output pins beautifully isolated. If you do come to need an Eagle component for that, I'd find it interesting to do. I'd make the pads a little longer than normal, to make it easier to hand solder. (With one wipe of a hollow-tipped iron to do each side.) But whichever package is most available might be best. A component macro for the SOIC 28 would be quicker.) At first glance, I thought the 0.5v threshold of the current comparator would be power wasting in low to medium voltage applications, but then I saw the current amplifier. That saves adding something like an LM833 to allow a sense resistor in the milliohm range. Ah, and it has separate Vss and Vso pins (like the IR2110 and IR21834), allowing separate logic and power grounds. Now an important question. Where is it planned to source the BLDC motors? :-) Erik ------------------------------------------------------------------------------ Special Offer-- Download ArcSight Logger for FREE (a $49 USD value)! Finally, a world-class log management solution at an even better price-free! Download using promo code Free_Logger_4_Dev2Dev. Offer expires February 28th, so secure your free ArcSight Logger TODAY! http://p.sf.net/sfu/arcsight-sfd2d _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
