> > If you are using a laptop perhaps the power adapter for the laptop
> > grounds the negative rail?
> 
> Actually I've disconnected everything now, I'm testing with just the
> parts in the circuit I attached and it doesn't work. (I already burned
> the computers COM port, luckily I also have a usb-rs232 adapter).

Oscilloscope ground clip providing the short to ground? 

-- 
Brent Brown, Electronic Design Solutions
16 English Street, St Andrews,
Hamilton 3200, New Zealand
Ph: +64 7 849 0069
Fax: +64 7 849 0071
Cell: 027 433 4069
eMail:  brent.brown@clear.net.nz


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