RS232 Opto Isolator

Hello:

Not having much luck in getting this circuit to work. Pretty sure the problem is the power supplied by DTR and RTS. The two lines are not controlled by the software so they are both at +10, or -10V can't recall as I am writing, but not +10 and -10 as required.

Wanted to try using a split power supply using two 9v batteries, but not sure how they should be connected in the circuit.

**broken link removed**

Thanks

It's probably not a good design for windows. Look at the more complex but workable schematics on the R.E.Smith Serial Communications RS485 site.