Complete newbie. Need labview help...

[mrbebu]

Hello,

I'm a mechanical engineering student at the State University of New York in Stony Brook.  I have a liquid metering device project that i need to build and it has to be controlled via labview on the lab computers at school.   The problem is, we got next to no training with the labview software and it is mandatory that we use it, so as you can imagine i'm in a little hole.  I have some programming experience with MATLAB, so I understand how programming works on basic level, but that is all at the moment.  

Anyway, the dynamic aspects of my project consists of a miniature water pump (3VDC), a normally closed solenoid actuated valve (12VDC), and a weighing scale (battery powered).  The finalized program idea is this:

1. the user enters in a desired volume of water to be dispensed in labview
2. labview will then convert the entered volume into whatever signal/units the scale is outputting into labview in 
3. labview will then energize the pump and the solenoid simultaneously 
4. water will then flow into a small beaker on top of the scale until a test condition is met between the inputted volume and outputted scale signal
5. Back to step 1

What i need to know is, what do i need for this to work through labview? Can labview supply power to devices or do i need another means? I'm assuming i need an I/O board, but this is all alien to me at the moment and i could use all the help i can get.  

Thanks in advance,

Tom 

[TCPlomp]

In hardware you have three 'contacts'

1. Pump
2. Solenoid
3. Weighting scale

I would connect the Pump and Solenoid via a Digital output and a relay or a relay card directly (a computer normally has not the power for motors or anything).

The weighting scale should have an analog output (0-5V preferably) and read by an analog input.

These first steps  of contacting should get you started. Have a look at the LabVIEW examples (hardware IO and controlling) and the LabVIEW Learning Center is here.

Ton

[mrbebu]

Can you give me an example of what kind hardware i can use? Something cheap, yet effective.  Also, what exactly is a relay card?

[yenknip]

Since the DAQ device is powered on USB, it can only output a few mA, which isn't nearly enough to power a solenoid. You will want to find a TTL relay board which is basically a transistor and a relay. The transistor is powered by the small current from the computer, which closes the power relay. a quick search finds the sort of thing you want

NI has hardware which can connect easily into LabVIEW without any fuss. Alternatively, you can use another vendor or data aquisition hardware and will proably need to communicate to the device drivers, which can be a bit more troublesome. If you want a quick and easy digital and analogue signals device, I would suggest the USB-6008, which in the UK is £100, which should work out at about £170US

The best thing I can suggest regarding software is following Ton's link to the learning centre, and playing around with LabVIEW then posting back when you have a feel for what needs to be done. Additionally, there are programming examples shipped with LabVIEW which can be found in the help->examples menu.

[mrbebu]

Thanks for the replies.  I just ordered labview 8.5.1 student edition so i'm not limited to the lab hours at the university and i can learn this as best as possible.  

I'm going to apologize for my lack of electrical circuit knowledge.  I've been reading a lot the past few days to try and familiarize myself.

I believe that our lab is providing the DAQ devices since they seem to be an expensive item.  So say for instance in the step where i want labview to power the pump and solenoid simultaneously, i assign 2 independent DAQ device output channels for each device and wire these channels into two inpendent relays on a TTL relay board that is typically powered by a 12VDC power supply.  Then each relay is then wired to the devices....?

What about the issue of each device requiring different operating voltages?  The pump will only require 3 VDC and the solenoid 12VDC.  

regards,

Tom 

Message Edited by mrbebu on 11-10-2008 10:27 PM

[Eric_R]

Hi Tom

With regards to the different voltages, you will need to deliver your own power for the instruments. The relay will just receive the 0-5 volt TTL signal for the purposes of turning the devices on and off. An alternative setup could be purchasing a NI-USB 6525 and connecting this to your 12 VDC and 3 VDC power supplies across the solid state relays built into this device.

[mrbebu]

Thanks for the link eric, but unfortunately (and fortunately) i'm a student and i can't spend that kind of money at the moment.  Upon further research, i think i'm going to have to use radioshack components for powering the devices via transistor switches driving a relays on a basic bread board, as described here: [url]http://www.jaycar.com.au/images_uploaded/relaydrv.pdf[/url]  

I know this is probably a laughing matter to most on here, but i don't know much about circuits at all.

Message Edited by mrbebu on 11-11-2008 05:34 PM

[RavensFan]

One of those ways shown in your link will work just fine for driving a relay.  I used a method like that when I needed to test a digital output (5VDC) controlling a 24VDC relay and it worked great.