This guide will run through the version 1.2 and 1.3 PCBs in parallel. I have done this because people who wish to program thier own PICs will probably be a lot more comfortable with the 40 pin DIP chip used in the revision 1.2 PCB than the 44 pin PLCC one used in the revision 1.3 PCB.
I have kept all the part numbers the same, and will make special metion of any steps that are specific to a particular revision.
If you wish to make your own PCB you can download the layouts either as a zip or a gzipped tar ball. Each includes Gerber files, PostScript files and PDF's. I am also able to supply professionally etched PCBs, complete with solder mask, through hole plating and silk screen print, please see the Ordering section for details.
Please NOTE: If you order a kit of parts, I will be supplying a UM245R module instead of the USB245M module. As the newer UM245R module is not pin compatible I also supply a conversion PCB and parts. Please see Appendix A for construction details. The following guide was designed for the original circuit. It is very important that you read Appendix A first, as this changes the order you must build the kit in.
I have split this guide up into 10 sections, each containing pictures, or screen shots to help you build the USB DMX interface.
Although it's fairly compact, and small, if somebody were interested in taking this forward to be surface mount then I'm sure it could be made a lot smaller and cheaper. If you're interested in doing this, and / or producing it commercially then please email me.
The USB Interface I chose is actually a surface mount device, and so I cheated and used the evaluation kit module that breaks out onto DIL spaced pins. Its made by FTDI and is called DLP-USB245M-G. This is probably the most expensive bit of the USB DMX interface, and although at the time I had trouble tracking it down, it seems to be readily avaliable now.
There is a databus shared by the SRAM, and the USB interface to the microprocessor. For PCB layout reasons I was only concerned about making D0-D7 the same on the interface and the microprocessor, as with the SRAM what you put in you will get out so it does not need to actually have D0 -> D0 etc, the same goes for the address bus.