Limit switches PCB schematic verification.

[Jonathan]

You've essentially connected the limit switches directly to the port with 10k pull-up resistors. In an ideal world this would be fine, however in reality there are a couple of problems. The main one is thatxthis set-up is very susceptible to electromagnetic interference, since the voltage/current through the switches is so low. The other potential problem is there is no isolation between the parallel port and the computer, so if something went wrong with the +5V PSU, then the parallel port would be damaged. Ideally you should run the switches on a 24V circuit and to do this you need to buffer the inputs anyway, so that's how you get isolation. If you search on google for parallel port breakout board schematics you'll find plenty of ways to do it.

[cncnoob]

You've essentially connected the limit switches directly to the port with 10k pull-up resistors. In an ideal world this would be fine, however in reality there are a couple of problems. The main one is thatxthis set-up is very susceptible to electromagnetic interference, since the voltage/current through the switches is so low. The other potential problem is there is no isolation between the parallel port and the computer, so if something went wrong with the +5V PSU, then the parallel port would be damaged. Ideally you should run the switches on a 24V circuit and to do this you need to buffer the inputs anyway, so that's how you get isolation. If you search on google for parallel port breakout board schematics you'll find plenty of ways to do it.

Awesome, thanks for getting back to me quickly!

I'll have a look and redesign this and put the new one up, if you could have another look that would be great!

[cropwell]

Opto Breakout

Here's a design for an opto-isloated BOB. Any comments from the team ?

Rob