Controlling coolers via LabVIEW .vi?

[Mardukker]

Hi
I'm a newbie trying to use LabVIEW to make a small control system by use of a thermocouple and coolers/electronic valves. I'm having a hard time finding a good way to control these coolers via LabVIEW, because I don't have any hardware yet, and my budget is low (it's a simple university project).

What would be the best way to control regular DC 12V computer fans via Labview? If possible, it would be good to control them digitally but with 4 bits or so...to have several degrees of power directed to the fans (but initially, on/off switches would be fine too).

Any help would be really appreciated from you kind folks,

Thanks!

Mardukker

[SanRac]

HI

You can use the Parallel Port of the computer to control the DC 12V computer fans. Parallel port is 25 Pin connector, in this 2 to 9 pins are the output lines.

Output of the parallel port lines is 5 V so you need to create some transistoried amplifier so that will help to drive the relay, and using the relay you can control any device (fans etc). I think it  comes under your budget 😆

Circuit - Computer > Parallel Port > Transistorised amplifier to drive relays > Relays to control the fans

Regards

Santosh

Message Edited by SanRac on 08-10-2009 11:54 PM

[Wayne.C]

Mardukker,

Parallel port should work fine.  Consider using something like the ULN2003A driver to increase drive levels.  Note that it includes the diode snubbers that are needed when driving inductive loads like relays.

[Alain_S]

ULN2003 is indeed a good, cheap solution 🙂

But I wonder how one can read a thermocouple in a cheap way ?!?

I suppose it's room temperature range, so you need a T type thermocouple.

I'm curious... ...

[Wayne.C]

Alain,

If I had to do temp and digital outputs, I would start by checking E-Bay and other auction sites and see if I could scrounge up a used NI USB-DAQ on the cheap.  If that didn't work out, I would use the parallel port and and ULN2003A to drive the fans.  For the temperature I would consider building a simple temp sensor board that had an IC to convert signal from TC, a uP to perform the A2D conversion and drive RS-232 port via a MAX202.  I've seen lot's of these in the past and some folks have even posted the uP code as well.  Some are even powered by the serial port.

[SanRac]

HI

I am agree with Wayne.C,

For measuring the temperature I can suggest LM35 , and user can use A2D conversion IC probably ADC 0809. User can communicate with this IC with parallel port only with the help of 74LS157 (8:4 Multiplexer). Parallel port input pin 10, 12 , 13 and 15 can be used for acquiring the data.

Now circuit for temperature acq is LM35 > ADC 0809 (8 bit data as output) > 74LS157 (8:4 mux because we have only 4 pins at input so data can be acquired 4,4 bit) > Parallel Port

Regards

Santosh

Message Edited by SanRac on 08-11-2009 08:35 AM

[Alain_S]

Ok guys, you build your own DAQ card/system to read in the thermocouple.

That way it's easy of course. But that's more electronic design than LabVIEW programming.

I also did lot of such µC based circuits (8051 based systems) in the past.

If you go that way Mardukker, I can suggest the AD 594 from Analog Devices.

Dedicated for thermocouple readings but then you still have to read in an analog signal

If you have some free I/O on that parallel port you may use the MAX 6674 from Maxim.

This one has SPI interface

Anyone ever tried to amplify a thermocouple signal and read it through the sound card?

Just a wild guess if that's feasible ???

That would be low cost !!

Message Edited by Alain S on 08-11-2009 05:42 PM

[Coq_Rouge]

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Alain S wrote:

Anyone ever tried to amplify a thermocouple signal and read it through the sound card?

Just a wild guess if that's feasible ???

Thay would be low cost !!

---

As a thumb rule no. Sound card are most often AC coupled with a bandwidth 20-20Khz. But you can make much fun out of a sound card. I have made a AC skin conductance application

[Coq_Rouge]

But if you put a thermistor, in an AC bridge setup, and then use synchronous demodulation...... So yes I guess you can do it

Message Edited by Coq Rouge on 08-11-2009 06:01 PM

[Coq_Rouge]

If you need help I think I can show you how to measure temprature with a sound card.