Got it working very quickly after a couple of redesigns.
My first etch came out pretty iffy, as you can easily see:
So, I redesigned the board a bit and transferred it.
Ah crap, forgot to mirror my transfer. Let’s try that again:
Nice. The only sketchy trace was the one that connects to the RXD line, but I tested it and electrically, it’s okay. So, I assembled the board and planned to find a broken USB cable and solder it onto the 4 holes at the top of the board.
Unfortunately I couldn’t find a USB cable, so… I made my own by taking a random piece of 4-conductor wire and soldering a PCB USB connector to it.:
Yeah, that didn’t work so well. My computer recognized that a device was plugged in, but failed to talk to it. I think it might have had something to do with the fact that the cables weren’t stranded. Or, I may have killed the FTDI chip because I applied a fair amount of heat when I soldered it.
So, it was back to the drawing board. I designed a new board with a built-in USB connector so that I could just connect it to my computer by plugging it in directly or by using a USB extension cable.
I’ve discussed the MITERS etching process before. It’s pretty great. Basically, the steps are:
- Print out the board design onto glossy paper with a laser printer.
- Sand down the board you want to etch a little bit to roughen up the surface.
- Clean the surface with acetone.
- Put the printed design and the board together and stick it through the laminator.
- Remove the paper quickly under water. I discovered the technique is to scrub the paper away rather than to peel it; the transfer comes out usually nearly perfectly.
- Throw it in ferric chloride and swish it around for 10 minutes.
- Wash with acetone.
I wired RXD and TXD together and tested it out. It worked!
Afterward, I put some male headers onto the device and stuck it in a breadboard to create the demo video above.
I’m pretty sure the entire device can operate with just the FT232RL alone. The rest of the components on the board range from somewhat important (ferrite bead, filter caps) to purely asthetic (debug LEDs). I bet you could get rid of it all and it’ll work fine. It’s more expensive than a typical MAX232 design (which probably totals about $2.50), but it doesn’t require RS232, which is kind of a plus. I’ll probably make a cute little MAX232 breakout board in the future as well, though.