Basic question : controlling a relay with a DIO

[marc france]

Hi,

I am using Labview 8.5with a 6229 PCI Card.

I would like to use this card to control relays using the DIO. Could anybody tell me if the inputs or outputs can be used as simple switch or  are they only 0-5V inputs/outputs? What I would like to do, would be to use an external power supply in serie with a Digital Input that I control with my program (level high/low in order to act like a switch)  

Sorry for this simple question but I am not familiar with this domain.

regards,

Marc

[smercurio_fc]

In the strictest sense you cannot use a DIO line as a switch because a switch has 2 terminals: in and out. A DIO line has one terminal. That said, if you consider one of those terminals as ground, then you can use a DIO line to sink/source current. In this case you can wire it in series with the relay. However, BIG thing to consider is current. The max current capability for the 6229 is 24 mA. Whether or not this is adequate depends on the type of relay you're trying to control. What kind is it?

[RavensFan]

Also Voltage.  What is the voltage of the coils for the relays?

With a separate power source for the relays of whatever voltage you need, you could also use a transistor and resistor to take the 5V low current from the digital output to switch on and off a higher current/higher voltalge supply to the relays.

[Drewski]

For switching 24 Volt DC relays on and off we use Opto-22 relays on a G4PB4 mounting rack to "boost" the 0-5 volt digital i/o values.  The digital i/o lights an LED which switches the Opto-22 relay which  can handle the 24 volts.  To set this up we have a standard "tray" of equipment, a 5 volt open frame power supply, a 24-volt open fram power supply, and a tbx-68 or scb-68.  The 5 volts supply powers the G4PB4 board and Opto-22 relays.  The 24 volt supply is used to open and close the 24 Volt relays.  The tbx-68 or scb-68 is used to connect the digital i/o from the 6229 to the G4PB4.  Depending on how you set it up, you may have to wire in the pull up on the 6229 and negate the logic used to control the Opto-22 relays.

Good Luck!