com port max voltage

**vtcom** · 10-19-2008, 07:21 AM

what is the max voltage you can feed pin 8 of a serial port?
and do any of you uses any protection to stop spikes from relays when they
open and close

**Rob Withey** · 10-19-2008, 07:58 AM

Originally Posted by vtcom

what is the max voltage you can feed pin 8 of a serial port?

See RS232 spec here : http://www.lammertbies.nl/comm/info/RS-232_specs.html

Originally Posted by vtcom

and do any of you uses any protection to stop spikes from relays when they
open and close

Use a snubber diode across the coil, standard thing to catch the back emf.

**vtcom** · 10-19-2008, 08:24 AM

most that link is over my head am i correct to believe it can take 25 volt

**Rob Withey** · 10-19-2008, 08:43 AM

Originally Posted by vtcom

most that link is over my head am i correct to believe it can take 25 volt

In theory, yes. However in practice it tends to be more like -12 -> +12v and I'd be slightly worried about putting more than that in. In any case I would put a current limiting resistor in series to reduce the chances of any issues.