Re: microcontrollers under $50?

Joe Strout wrote:
In article <4653A926.1020105@xxxxxxxxxxx>,
"Wayne C. Gramlich" <Gramlich@xxxxxxxxxxx> wrote:

But a bigger problem for me is all the support stuff these chips seem to require -- capacitors, resistors, etc. An internal oscillator does reduce the part count somewhat, but not to zero, right? How's a poor software guy like me supposed to know what these parts are and where they go?
Well, actually, there are no other parts, just supply 5 volts.

Really? I didn't know that. But in a board like this:

http://www.futurlec.com/ATMEGA_Controller.shtml

...all those extra parts really aren't adding any value beyond breaking the surface-mount chip out to header pins? I see a voltage regulator, and you did mention that; but I also see about a dozen capacitors, five or so resistors, another IC, and a little oval-shaped thingy that I don't know what it is (the crystal maybe?). One of the resistors is serving the on-board power light, and so counts as part of the power supply. But what's the rest of that stuff for?

The oval thing with the two orange capacitors on top is the
crystal oscillator (not strictly needed.) The round black
thing to the left is the reset button. The blue trim pot
is the contrast adjustor for the LCD daughter board. The
black chip in the upper left is the Max232 level converter
along with the requisite 4 charge pump capacitors. The rest
is power supply, on LED and of course an ATmega128, which is
a really, really sweet microcontroller that is only available
in surface mount.

[snip initialization]

Actually, a well designed board does not really help
get the first program working.

Well, it does help with all that other stuff which you say isn't needed but which I can't help feeling must be doing some good, since all the controller boards have them. :)

You missed my point. If I give you a well designed board
complete with schematic, you will probably struggle for
quite a while before you get the first program running
on it. There are a lot of icky picky details that must
be right before you get your first blinking LED.

What helps is that the board comes with a demo program that
somebody else has already figured out.

That depends on the board. With the ARMexpress, the compiler is onboard. The complete steps to get going are pretty much

1. Connect a serial cable to the ARMexpress serial input
2. Fire up a terminal program and connect to that port
3. Type
PRINT "Hello world!"
RUN

Getting started with the AVR Butterfly, for example, is a LOT more involved despite the serial bootloader. (Or so I gather, though I couldn't find anyone or anywhere that could actually explain how to do it.)

This is my point. The AVR butterfly is a wonderful board
for the money. But it is just an overpriced paper weight
if you don't know how to cram programs down into it.

The real problem you are facing is a documentation problem.
There is tons of stuff out there that makes a fine and
dandy robot controller for a low end robot, but the amount
of stuff out there with adequate documentation is much harder
to come by. The spec. sheets for PIC's and AVR's are complete
but hardly easy reading.

Yes, that's true. There's also a difference in convenience. You said yourself (IIRC) that you like to put your PIC or AVR on a carrier board that gives you buttons, lights, and other conveniences (which I would guess includes header pins, mounting holes, a power supply, etc.).

I posted my controller28 board in a separate post. In short,
power supply (yes), programmer connections (yes), interconnect
bus (yes), place to connect a reset button (yes), everything
else (no).

I think this depends partly on what you're doing -- if you're working on a prototyping breadboard, or designing your own PCB, then a bare chip (or a DIP board, like the Stamp form factor) is quite convenient, and a big board with header pins is actually more of a PITA. But if you're trying to avoid extensive breadboarding and just bolt a reliable controller onto a bot, then a bare chip or Stamp board is a PITA and a board with headers is more convenient.

It depends upon the robot. If you need an H-bridge or two,
and your controller doesn't have that H-bridge, you are in
for some real pain. If all you want to do is run a few servos,
a pretty bare bone microcontroller might work out.

What got me excited this week about the Futurlec mini-boards is that they've picked a couple of standard connectors, and made a lot of small boards that (it appears) you could just cable together to make a wide variety of complete packages. Start with a controller, add a switching regulator if it lacks one, throw in a sound (or even MP3) board, an SD card reader, a motor driver or two, and pretty soon you have a bot.

They are on the right track, but not all of the board use
the same connector. More importantly, you have to figure
out the sub-program for each and every interface board. In
addition, you have to figure out how to get one microcontroller
to juggle it all *at the same time*! Some are easy (push
buttons), some are much harder (3-axis accel.)

But in the meantime, I find myself doing a lot of breadboarding, and preferring the Stamp form factor. I'd be happy with a chip too if I could just connect a serial cable and talk to the dang thing from my Mac. It sounds like with the right tools, I can almost do that with the Atmel chips, but as you say the docs are lacking.

An Atmel chip, plus Max232 (+4 1uF capacitors), plus boot loader
will do the job. I'm sure if you visit AVRFreaks, they will tell
you all about how to do it.

Hmph. Maybe I'll buckle down and figure out the AVR toolchain. But next month -- this month, I have a bot to build...

Good idea -- build a little, learn a little; build a little more,
learn a little more, repeat.

Later,

-Wayne
.