Using external trigger channels with PCI-1422

[sspencer]

I need to trigger some 5 volt relays with my PCI1422 board similar to the way it is done with digital I/O on a standard board. Can this be done using the trigger channels? I have tried this and only get a 2V state change...

[Morten]

Hi,

How much current are your 5V relays pulling? Have you tried to measure the voltage change on your 1422 trigger lines with a Voltmeter without connecting it to the relays? The Trigger lines on the 1422 should give a 5V TTL signal, so something must be pulling that signal down.

Hope this helps.

Morten Jensen
National Instruments

[Doug Mumford]

I believe the 1422 outputs are "sinking", as opposed to "sourcing". So you have to connect the relay from +5 through the 1422 to common, or use a pull-up resistor to +5.