Thursday, September 22, 2011

Another breakout from DP...

A while ago I received another free pcb from Dangerous Prototypes in the mail, but alas I had the wrong format chip on hand (I used the larger soic version on a project a month ago) so it had to wait a bit before I could populate it (Digikey didn't stock the ssop version, but Mouser did).

This board is a breakout for the MCP200 (described here).  Overall it's relatively simple little board: the main chip from Microchip, four resistor/led pairs as indicators, a 12 MHz crystal with caps, a pullup for the reset line, some power filter and reserve caps and a ferrite (good for grabbing power off the usb line).  The MCP220 is an odd little device though - it's happy on Windows, not so much on Linux or OSX (inherent in the way it interacts on the bus I think - I'm not all that familiar with the sub substructure and don't have enough free time right now to really dig into it).

The quality of the pcb is quite good.  There are some interesting layout choices (variability in cornering decisions, trace separation) but they won't make any differences at the speeds the signals travel here.  I suspect that half the board (the usb/power domain) was done at a different time than the other half.  I did make a stupid mistake by reversing the tantalum cap (hint: you over draw the usb current) but it didn't blow up releasing magic smoke so I was happy... I replaced it with a new (but larger one than spec).

It's a nice little board that serves it's purpose as a breakout for the chip (intended to be a competitor to FTDI in the USB->UART market).  The signals (including a few GPIO lines) are brought out in two rows for prototype boards.   Having as well the pwr/gnd and serial signals at the far end makes it practical to use as a serial connection to other devices.

If I had to change one thing about the board it would be to add labels for the output pins/holes... The one thing I really like about putting together other people's designs is that I always end up learning things - the differences in the way I would do it jump out - sometimes I end up liking my way better, sometimes I find a better way of doing something (and that's great).