USB-to-Serial Module based coders cable

[pboese]

This latest iteration of the USB-Serial Coders Cable uses a hi-speed digital isolator that solves all the leakage problems that I was seeing before. Now the DC and PC are electrically isolated from each other. The power state of either deivice is of no consequence to this latest design. Current cannot not flow from one device to the other now. I was concerned that leakage currents might damage the DC or the USB chip. Now those issues have been solved.

The following picture shows a VERY HACKED up Rev B pcb with the new isolation circuit married up with the DLP USB Module.



Another copy of this will be made and sent to a Mac user for testing. Now I can seriously think about laying out a new pcb. What do you guys think about enclosing the board in a translucent ice blue case with a nice blue LED to indicate data flow?

[WHurricane16]

This is just an awesome project. Good luck, Axlen!

[Segata_Sanshiro]

lol it really looks hacked, and I have no idea about this kind of things. I really admire the work people like you do.

[pboese]

Well I plugged the *HACKED* board into the DC *LIVE* and blew an input. An input on the digital isolator, not the DC serial port thankfully (whew) 8) Unfortunatly the DC's serial plug is not designed for HOT PLUG use. Ideally the ground and power would be applied first followed by the IO pins. So that brings me to the need to create an input protection circuit. The TVS (ESD) input diode array I'm using does nothing to help protect against this problem, just kiddes walking across the carpet and making pretty sparks when they touch stuff :P Back to the drawing board

Thanks for the encouragement everyone.

: Of course I could just take the easy way out and put a warning note on the cable warning the end user to turn off the DC before attaching the coders cable to it. :

[WHurricane16]

[quote author=Axlen link=board=hardware;num=1093196907;start=30#43 date=10/31/04 at 22:23:52]: Of course I could just take the easy way out and put a warning note on the cable Â*warning the end user to turn off the DC before attaching the coders cable to it. Â* : Â*[/quote]

Well, Joe Snuffy won't be buying this but Joe DCDev will....so maybe just issueing the warning will suffice.

[Alexvrb]

Make sure you use a phrase including "under penalty of death". Unless you feel it is easy enough to resolve it in the cable design.

[pboese]

Well I took the time to finish up my Bravado Rev B board and fixed the problem with the smb package layout. I had to use a kluge to do it and it looks awful, but guess what, the darn thing actually works. Here's some pictures of the awful looking thing.




So there it is, my first 4 layer pcb with an ugly fix. Work continues on another version as previously mentioned.

[Alexvrb]

Damn, a hardware kluge. Still, if it works, kick ass.

[pboese]

This is just ugly but true side of hardware development. Unless of course you've got many years of experience and a lot of luck ;D You can screwed by vendors obsoleting parts, errors in technical data, etc. In this case it was my fault since I should have been more careful selecting the package layout for the FTDI chip. It was kind of confusing. I did not realize that there are two different pad pitches for the LQFP32 package. .8mm for the 7x7mm package and .5mm for the 5x5mm package. Of course I choose the wrong one :P Now I know better of course. :

[DreamDogg]

Wonderful project. I will be interested in buying one when it's finished. I would regard the protection circuit as an extra feature, and it would justify a higher retail price in my mind. I am willing to pay a little bit extra for a product that's idiot-proof.