Serial cable output a logical high and low using labview

[uncc]

As part of my senior design project I am using labview to assist in designing a computer workstation for a handicapped individual. To make it easy for him, the individual will be able to select a button in labview to activate an actuator and make his dual monitors rise up or down on his computer workstation. A serial cable is being used to output the voltages and will be wired into two relays. A voltage converter will also be used and wired into the relays.

My question and problem is first can a serial port output a logical high and low and if so what pin or pins are used. If a serial port does work then what do i need to do in labview to make the serial port change from a high to low. While i was playing around with labview i created a simple push button and got enough voltage out of the serial port to turn on an led light but not turn it off. This makes me assume that my idea of controling an actuator would work but i defintely need some help. I am new to using labview so thanks in advance for any help you can provide. 

[RavensFan]

You can used 4 pins to output a digital signal  DCD data carrier detect, RI ring indicator, DTR data terminal ready, and RTS ready to send.  You would create a property node for those pins, change them to write, and wire an Enum to them where the important values are Asserted or Unasserted to change their output.

Those outpus probably might not have the voltage, and certainly don't have the current to drive a relay.  You could use a transistor to drive a higher voltage circuit that could power a relay.  Search the forums.  There are other message threads that discuss this, and probably several of them give an example circuit.

I can't comment on your push button LED experiment without knowing how you programmed it, or how you had the push button and LED wired.

[ABCPrograms]

Hi,

wouldn't it be easier to use the parallel port of a PC.  Cause this is already a very low cost Digital output port.

Connect the outputs with a opto-coupler cause it can't handle current, but it works easy and perfectly fine

[ABCPrograms]

This is an example on how to use parallel port is Digital in or Digital out

[uncc]

Thanks for your help. I got labview to switch from positive to negative voltage with a simple press of the button. After working on my senior design project I need this feature to do a little more and can't seem to get it to work right. Instead of switching from positive to negative i need it to switch from postive to zero. This way when a button is pressed it output postive voltage until the button is pressed again and then no voltge or zero volts is produced. Thanks for any help in advance.

[RavensFan]

Are you using a serial port or parallel port?

Serial ports are either a positive voltage (+3 to +25V)  or negative voltage. (-3 to -25V)

Parallel ports are either a a positive voltage (nominally +5V) or zero (nominally 0V).  But the actually voltage levels are permitted to vary somewhat from that.  So zero volts might not truly be 0.

[smercurio_fc]

move to here: http://forums.ni.com/t5/LabVIEW/Switching-from-positve-or-negative-voltage-to-zero/td-p/1517630