5 volts are on the DAQ when the comuter is shut down

[sara]

i have a problem with DAQ when i shut down the computer a 5 volts are on the digital output port thi means all the relays are on ?

can any body help me?/

[silmaril]

QUOTE (sara @ Apr 30 2008, 09:25 AM)

i have a problem with DAQ when i shut down the computer a 5 volts are on the digital output port thi means all the relays are on ?

I don't know which exact board you have, so I assume it's some NI multifunction DAQ board.

The digital IO lines on those boards have pull-up resistors, which means they will always go to their high level by default. This is the documented behaviour.

If you want to switch off whatever you connected to the digital outputs when turning off the computer, you might use inverse logic in if your external hardware allows this.

But please be aware, that the output levels may still change to totally undefined states, if you disconnect your computer's power cord!

[Ton Plomp]

QUOTE (silmaril @ Apr 30 2008, 10:55 AM)

I don't know which exact board you have, so I assume it's some NI multifunction DAQ board.

The digital IO lines on those boards have pull-up resistors, which means they will always go to their high level by default. This is the documented behaviour.

If you want to switch off whatever you connected to the digital outputs when turning off the computer, you might use inverse logic in if your external hardware allows this.

But please be aware, that the output levels may still change to totally undefined states, if you disconnect your computer's power cord!

Some devices (M-series?) have tri-state digital lines, and I believe you can set the 'default' state for those.

There was a change between E (6052) and M (6221) that changed the behaviour of the digital lines.

Ton

[Tim_S]

QUOTE (sara @ Apr 30 2008, 04:25 AM)

i have a problem with DAQ when i shut down the computer a 5 volts are on the digital output port thi means all the relays are on ?

can any body help me?/

Assuming that you have a board that outputs a logical "high" by default... One means we used to resolve this is to have one output that controlled an on-after-day physical relay. The relay would provide control power only after the PC had control of the outputs. I unfortunately forget the relay logic we used.

Tim

[Irene_he]

QUOTE (sara @ Apr 30 2008, 04:25 AM)

i have a problem with DAQ when i shut down the computer a 5 volts are on the digital output port thi means all the relays are on ?

can any body help me?/

Shutdown computer does not mean there will be no power into your DAQ card. So the DIO will maintain it's state unless you programmatically set the DIO to low when you exit your software. Only when you power down your DAQ card (if it is USB DAQ, just unplug the USB cable), then the DIOs will go back to it's default state. Some DAQ DIOs has default to high, some to low state, depends on spec.

Irene