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Generate a Pulse Over RS232/TTL

I'm using labview in connection to a measurement tool that makes a connection to computer via TTL. To connect, I have a USB to RS232 cable, and an RS232 to TTL adapter.

My goal is to use Labview to send a 5V pulse of set length over this connection to indicate the start of a measurement period, could anybody please explain how to do this/whether it's possible without adding a DAQ?

Thank you!

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Message 1 of 7
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This seems like a pretty strange way to send a pulse, so I'm guessing you're trying to do this on a budget?  What exactly is on the other end of the connection?  How long of a pulse do you need?

 

I'm fairly certain that every serial byte has a start bit and a stop bit and that those bits are always inverted from each other (start =0, stop =1) so the longest TTL voltage pulse you can make that doesn't have a drop to zero is 8 bits in a row.  If you have a baud rate of 300, that's 8/300 = ~26 ms long.

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Message 2 of 7
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Not sure your exact requirements for this, but you can control the individual lines of your rs232 via the modem lines settings propery node.  Ive used this before to control relay switches, simple stuff though. I attached a link that should help.

 

Control Modem Settings



-Matt
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Message 3 of 7
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I know it seems strange, but it's for a piece of medical equipment (EEG) so it's sort of a strange application. The pulse only needs to be a minimum of 4ms long according to the manual, so that would work! Do you mind explaining how to do that? This is a brand new job for me and I've never used Labview before.

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Message 4 of 7
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Well you basically need to just open the serial port you plan to use and then you can toggle on and off the control lines. Do you know which line you are wiring to the input of the device?

 

 

Basic Serial Port Usage

Property Nodes

control line Property node



-Matt
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Message 5 of 7
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Oops, that was a repsonse to the other person's answer! Thanks for all the helpful links Matt, this looks like an easier way of doing it. 🙂

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Message 6 of 7
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While I agree that you should be able to do what you say you want done with the equipment you have described, next time you need to do something like this, you might want to consider something like http://www.mccdaq.com/usb-data-acquisition/USB-1024LS.aspx ($89) as it is more suited to this task. They even have LabVIEW drivers available for their hardware.

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