[pminmo]

Part of my goal with my open source work is 3977 boards that the complete DIY'er can do. I believe we have accomplished that with the single sided version of the board. The other part of that is a professionally manufactured board that the hobbiest can build, repair, and is low enough in cost, it makes sense for the hobbiest. My original DS board, while I have made a bunch of, didn't really meet my goals for cost and repairability. BUT, I'm close to sending a design off for proto manufacture that I believe meets my objectives. This is my debate question, and what has me held up.

As is, it is not opto isolated. It is isolated to a PC's active pins by 10K ohms of resistance. If there is a failure of the 3977, 10K through the 74HC14 should be a failsafe protection for the PC. The ultimate protection though is opto isolation. But opto isolation has it's downsides as well. Extra power supply, not compatable with all parallel ports....., increased component cost.

Ultimately I hope to have a blank DS, solder masked, silk screen pcb that I could offer for sale to those who want the 3977, want to build their own electronics, but don't want to fool with etching or milling their own. My intent is not to profit, but not to loose money either. The cost goal for the blank pcb is $7 +/-.

This board would use the 3977SED (larger) part.

So which should I do, non opto or opto? Or not do it at all?

Phil