Connecting NI9403 output to input

[tcmoore]

Hello,

I am using a NI 9403 DIO module in my project.  I want to connect one of the DIO pins, as an output, to the collector end of the PC845 optical switch.  The output level would be set to hi or +5v.  Then take the emitter of the optical switch to another DIO pin, as an input.  Can I do this without using any current limiting resistors?  Does the NI 9403 current limit it's output?  If I have to use a value, what value can be used with the pull down resistor that is on the input?  What is the value of the pull-down resistor on the inputs?  I don't see a spec for it in the manual.  I basically want to use the optical switch to allow one DIO output to drive the condition of the DIO input based on the switch being turned on or not.  The PC845 has a Vce= 1v.  Or am I going to have to configure the circuit in the traditional open-collector configuration?

Your help is greatly appreciated.

Todd Moore

[The_Red_Barron · Accepted solution]

Hi Todd,

You should be able to connect the collector directly to a digital output line and the emitter directly to an input line.  When the optical switch is active it is similar to the DO and DI pins being shorted together.  This will not cause the device to source or sink more current than it can handle.

You can find information about overcurrent and short-circuit protection on page nine of the manual: https://www.ni.com/docs/en-US/bundle/ni-9403-getting-started/page/overview.html

Regards,

[tcmoore]

Thanks very much for your help!!

tcmoore