I have a Spartan 3 starter kit. Im going to build an expansion board that will have some more components on it. does anyone know where i can get some examples? or guides to do this? i know im going to use a standard 2x20 right male connector, and i the pin functions. but an example board would be most helpful. i also want to attach some sma connectors on it to get testpoints.
the plan might be.... build pcb layout, have expert review design, produce gerber, and send to be printed. someone recommended 33each.com
Hmm... 2x20.. Sounds like the connector that Digilent uses on its boards. They also sell accessory boards, which seemed to be reasonable priced. They won't have SMA connectors, though. Even if you don't buy from them, you may get some ideas from looking at their site
And no, I don't work for them, but I have bought some boards from them.
thanks for the reply. yes ive looked at them. but they dont share pcb layout files. i would like examples that i can use for like... dimensions and component placement examples. maybe something that utilizes different layers.
You sound vague about what you want the expansion board to do. I know I have the equivalent of "writer's block" when starting a new design. I often start with a vauge idea of what I want, and it takes me a while to decide what I really want. I sketch a lot of block diagrams, most of which I toss. It's tempting to add feature after feature, but start with simple designs at first. Be prepared to make mistakes. Hopefully you'll learn from those mistakes. The CAD package I use is EAGLE. The version I bought has a board size limit of 100mm x 160mm, which is roughly 4" x 6". 4x5 or 4x6 is also a good board size if you use the $33/bd company, and other PCB companies. When it comes to placing parts, look at your block diagram and schematic diagram. Parts that are nearby on the schematic should be nearby on the board. Connectors should be near the board's edge, etc. You can make paper cutouts of the parts, which you place on a piece of paper that represents your board. You can then shuffle parts around until you are satisfied with the placement. Again, looking at web sites that sell board-level products (e.g. Digilent), should give you some ideas on placing parts.
If you are using Digilent's Spartan-3 Starter Kit, then a word of warning: Most (or at least many) of the pins on expansion connectors are located in various IO-blocks that contain also the pins connected to the development board's leds, 7-segment display, push-buttons, slide-switches and what else. And as these use only
2.5 V levels, you have to use IOSTANDARD = LVCMOS25 also for your own I/O-pins in the expansion connector, as one cannot assign different levels to the pins in ONE and SAME IOB. (I realized this only when the ISE started giving error messages about different voltage levels...)
What I built is a simple opto-isolator card, with which I can control (not very fast though, because of the optos...) my TTL-level contraptions without fearing frying the Spartan-3. There are 16 output-lines and 8 input-lines, and I use the B1-expansion connector, because its pins are not shared with SRAM (A2 would work as well). I built this on a stripboard, with almost all the components sitting in DIL-16 sockets (except the regulator which feeds the 5V-side of the board). If I had a digicamera at hand, I would post a photo of it...
I guess you have the user's guide which details the pins. If not, then the copy can be found at Xilinx' site:
And indeed, Digilent has many nice expansion boards: