Review of a small motor controller schematic.

[EricVanWyk]

Originally Posted by AustinSchuh

Does anyone know how to solder a 20-hsop package that the MC33887 comes in? It has a large pad underneath it, which makes it harder. Do I put solder on the pad, place the chip on the pad, and then warm it up with the hot air until it melts? The naive way is to just apply lots of heat until everything is hot enough, and then it should be soldered on, though it might not work afterwords...

I've had good luck using solder paste for those sorts of things. If you have a beefy enough iron, you can melt the solder paste from the other side of the board through a via. Since the HSOP only has pins on two sides, it would probably be easier to just extend the middle pad and heat it on that side. If you have a hot air pencil, use that instead.

Originally Posted by AustinSchuh

Part of the problem is that I was under the impression that all capacitors are created equal, so I thought I'd worry about that later. Thanks for the heads up. I'll work on figuring that out.

Capacitors are dirty stinking liars. If they say "1uF", they mean "It will be 1uF, so long as you don't do something silly like apply voltage to it or hit it with a frequency." Take a look at a Y5V capacitor sometime - it dives to ~20% of its nominal capacitance when you bias it with half of its rated voltage.

Also, the effective series resistance can be just as important (or more important) as the effective capacitance.

Originally Posted by AustinSchuh

Thanks! I feel better about reading 5 volt inputs now. I read the spec sheets, and at least for the old motor controller I was looking at, 3.3v registered as high, so "5V" outputs aren't a problem.

I got in a small fight with the 33887 with regards to 5V tolerant. Don't worry, you are fine. The 33887 can handle 3.3V inputs just fine, but it has very small pullups to 5V. The chip I was driving it with couldn't handle its inputs being pulled above 4Vish, so I had to buffer it.

Originally Posted by AustinSchuh

I looked around online for about 2 weeks looking for an inexpensive micro-controller that would support CAN. I couldn't find any ones that were below $10, if I remember correctly. Any suggestions? $10 x ~10+ adds up a lot faster than $2-3 x ~10+. And I'll learn a lot implementing the bus

My suggestion was to use a standard bus protocol, rather than create something like a standard bus protocol.


I think you should contact one of the Luminary people on this forum and ask for 10 samples. I'm positive they'd love to help out a fellow FIRST community member.