Trying to send out a low (ground) on pin 4 of serial port. This is used to trigger a Furness Micromanometer to capture the current velocity value.

[DanNatCorning]

I'm trying to configure the serial port (com 5) to output a low (ground) on pin 4 , in order to trigger a Furness Micromanometer to capture the currrent temperature/velocity.  I'm having no luck finding any examples that don't involve sending strings.  I want to send a ground out on pin 4 once per iteration, in order to capture the velocity measurement.

[Dennis_Knutson]

You use a VISA property node and then select the property Modem Line Settings.DTR State. Change it to write and right click on it and select create constant. I've only used the Asserted and Unasserted state to apply the +12/-12 volt (typical) signal of RS-232. There is also an Unknown state that you can write to it. I'm not sure if a 0 volt output is the unknown state.

[tbob]

I don't know of any serial port that can send a ground on any pin.  RS232 protocol states that the signal levels shall be +/-12 volts.  I would not count on the unknown state to be ground.  I think it is floating and can be any voltage between +/- 12.  You could build an interface that has a relay.  The interface would have to be powered by 24 volts with an offset of 12 volts.  That way -12 volts is the ground, and +12 volts would be 24 volts on the interface.  Sending -12 volts to the interface would keep the relay off.  Sending +12 volts would make the relay (24 volt coil).  The relay contacts could send the ground to pin 4.

[Ray.R]

Dan,

Would you consider using the parallel port?  This way you can latch a value.  (Low or high).  It is not easy to " ""latch"" " a value using the serial port.. 

JLV