Hi,
There are so many PIC micro controllers out there, I’m having a difficult finding out which one is best for a small robotics project.
I’ve been looking the most at the PIC18F4550 as it seems to be pretty powerful and has a slew of input pins.
What do you guys think?
Thanks in advance,
Nathan-d
It’s a good chip. I’ve worked with it. Pick up a PICDEM FS USB Demo Board, and you’re good to go.
However you’ll give up about 1/2 your RAM and CODE space in support of the USB. If you don’t need USB (you really want to trail a FAT USB cable?), then go with the 18F4620 family.
I’m using the '4620 in my 'bot designs. There is a $15 “QwikFlash” board (PICBOOK.COM) available. It’s about 4" square, a little big, but quite usable.
Alan KM6VV
Can I just the 18F4550 without USB? Like this: sparkfun/commerce/product_info.php?products_id=21
Also, with one of these chips do I need to buy a programming board to download my program?
Thanks for all the help,
Nathan-d
You certainly can, you just have less RAM/FLASH, and a few less pins. I have developed 'bot code on the previously mentioned board/chip.
I have this little board as well. Yes, you’ll need an ICD-2 or compatible programmer, or use the boot loader that’s available for this board/chip.
Alan KM6VV
So even if I remove the USB support, half the RAM/FLASH is still taken up?
In other words, you’re saying that if I don’t care about USB (which I don’t), then I should look at getting another chip?
I still need a pretty powerful chip. I need to control servos (so generate PWM signals), do floating point math, possibly parse data from a vision system, etc…
On actually programming the chip, you said something about a “boot loader.” Does this mean I can use free software and not have to purchase a physical piece of hardware?
Nathan-d
That’s about it. Here’s some statistics for two builds on the same set of files Hitech C PICC18 compiler
[code]Program statistics: PIC18F4550
Total ROM used 25469 bytes (77.7%)
Total RAM used 752 bytes (73.4%) Near RAM used 16 bytes (16.7%)
Loaded 3DoF_C.cof.
BUILD SUCCEEDED: Thu Mar 20 16:20:01 2008
[/code]
[code]Program statistics: PIC18F4620
Total ROM used 26012 bytes (39.7%)
Total RAM used 761 bytes (19.2%) Near RAM used 16 bytes (12.5%)
Loaded 3DoF_C.cof.
BUILD SUCCEEDED: Thu Mar 20 16:21:39 2008
[/code]
But I believe you can “steal” some RAM back.
The '4620 (and some others) are basically pin-compatible, if not hardware function compatible. Same power (40 Mhz)!
The Microchip website has the info on the project. As do several other sites: Look up the PICDEM board for the files.
pic18fusb.online.fr/wiki/wikka.p … a=WikiHome
greta.dhs.org/UBW/
usb.org/developers/docs/
sixca.com/eng/articles/usbst … index.html
forum.sparkfun.com/
usbcnc.com/
Once you have a chip with the boot loader installed, there is a PC app “PICDEM FS USB” that will load your app, and run it.
Alan KM6VV
Yes, you need a way to program the PICs you use. I highly recommend the Olimex ICD2. I have one and have never been disappointed in it. It will program any PIC or dsPIC you might want to use. This not true of all programmers. I recommend spending the extra money and getting the ICD2 as it can be used for debugging as well as programming. I have read about so many problems with other programmers, and personally, I don’t need that kind of frustration. You will thank yourself for spending the extra money on the ICD2, which works with MPLAB perfectly.
8-Dale
I’ll see if I can get that programmer board, it’s kind of expensive though…
Thanks for the statistics and links Alan. I had no idea a chip with “USB support” would have most of its resources taken up, that really stinks and should be made more clear.
I really don’t know very much about PICs, does anyone have any more recommendations for me? It seems like all the PICs are priced very low, so price isn’t a problem. What’s the most powerful PIC for me to use? I know Alan suggested the PIC18F4620, but I just want to see if there are any other recommendations.
Thanks for the help guys,
Nathan-d
