Author Topic: Parallel Port interface to a relay.  (Read 2774 times)

G. Hoffman

Parallel Port interface to a relay.
« on: September 09, 2012, 05:57:25 AM »
Alright, so I need to add spindle on/off to my CNC machine, which more or less means a relay.  My break out card uses TTL buffers for isolation and to keep the load on the parallel port low (it needs 1mA per pin, or so it says).  So far, great.  My question is, is there any reason to have any addition interface electronics between the relay and the interface card?  I know it isn't required, but is it a good idea?  I suppose a diode across the coil, right?  It's a non-latching relay - an Omron G2RL-1A, 12A for the switch, 5 volt coil, which is where the TTL is running.



Re: Parallel Port interface to a relay.
« Reply #1 on: September 09, 2012, 06:04:48 AM »
Depends on the specs of the interface card, how much current it can put out and so on, but a mosfet (and that diode across the coil to get rid of the voltage spike) couldn't hurt