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LabVIEW - VISA COM Device - How to use Hex protocol to receive Data

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Hey everyone!

 

I am pretty new to LabVIEW and data collection, so this might be a pretty easy question.

I want to read the data from a Extech Instruments HD755 device, this is connected via USB to a COM Port.

I can see the device in MAX and I am able to open the VISA test panel.

I simply don't know what command I have to send now, neither I know how to search Google for this (I've tried several commands, but they didn't work).

I attached the Communication Protocol from Extech and my first try of a VI.

 

Thanks a lot in advance.

Tobias

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Solution
Accepted by topic author PTobias

Can not open your vi, I am at lv2011

Communication protocol does not say which commands to send. If no other information, it is either trial and error, and/or ask manufacturer for example in any text language, it is easy to get order of commands if it is the problem.

 

I would try something like attached as a first test, may be you need to send several commands (0x04 then 0x01) before it starts transmitting

 

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go to your max , check your port first then open test panel and check your comment
if anything is ok about your comment jump into labview visa port programming
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It works, thanks so much!

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Hi, just a note to everyone coming from Google - for the attached VI to work, do not use the VISA driver wizard to install the driver. Instead, install the USB to UART Bridge VCP driver - http://www.silabs.com/products/development-tools/software/usb-to-uart-bridge-vcp-drivers

 

Have fun automating!

 

 

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Also important to note - this is valid for any HD7xx model (I am using a 750), you should read 11 characters, not 10, and put the 'read' operation without either of the 'write' operations in a while loop, without a 'wait'. Labview should then provide values at the same rate they show up on the Extech.

 

 

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Yet more advice - the number displayed does not contain the minus sign. You should negate it if the second bit in the fifth bite is 1 - that bit indicates negativity. Also, it doesn't return a number if the pressure goes above or below the limits - that's because it switches to protocol 0x57. Fill the false part of the case structure with a note to the indicator to display 350 or -350 depending on which limit it hits.

 

Also a really neat thing is that by keeping it a loop telling the Extech to turn on the backlight every few seconds, you can keep it nicely lit and visible, which you would not be able to any other way! (it normally turns off after 30 seconds, at least on my HD750)

 

I've attached a file with all these modifications.

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Oh, and one last thing - for many purposes,especially if you're logging data, you will need to keep the pressure meter on indefinitely. Just hook up the power jack, hold 'hold' while turning it on until you see an inverted 'U', and bam - 24/7 pressure logging!

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