I need to detect the temperature of the water in the waterbath, and then send the data to the pc. The PC then needs to check the temperature and either start heating (using resistors) or start cooling (using a large fan ). I know I'd need an ADC, a thermistor and a DAC, however being a biologist, I do not have anything more than a basic idea about the elctronics involved. A search on the net has thrown up loads of sites which give circuits for interfacing an ADC/DAC with the pc, etc. however, I still don't know how I could use those circuits in my design. Can anyone please help me here ?

Regards
Mohan

 

You needn't get invloved with the electronics. You could use the LabJack USB data acquisition and control device. see "www.labjack.com":http://www.labjack.com . You could use this to monitor temperature and control your heating/cooling devices.

Audon Electronics offer the TP-200 temperature probe and the RO-16 relay board for the LabJack. The RO-16 would be used to switch power to the resistors and fan. see "www.audon.co.uk":http://www.audon.co.uk .

The LabJack comes with simple data logging software, but there is also the optional DAQLab software package. With DAQlab you can acquire temperature data, display your data on graphs, and you can construct control sequenecs quite easily to fully automate your process. see "www.daqlab.com":http://www.daqlab.com

 

Use LabView, the serial or parallel port, a temp sensor, and some relays for the heating and kooling. Labview could even make the temperature constant and not varying, PID control.

hope it helps

 

Thanks for both the replies.
However, the problem I face is not as much the s/w as it is the hardware, since I can code for the s/w. You mentioned relays. Are there any resources on the net where I can get the circuits or any details regarding them ?

Thanks
Mohan

 

You can find a mickey mouse explanation of relays here:

"http://www.howstuffworks.com/relay.htm":http://www.howstuffworks.com/relay.htm

it is as simple as applying voltage to a coil that closes a circuit (basically an electronic switch). You can achieve this by using the parallel port to send 5V between the pin and ground to activate a relay that closes your fan or resistor circuit.

 

What's wrong with just using a commercial heating and cooling thermostat? If you need very tight, precise control you need to hire someone who knows what they're doing. If you just need it to
be pretty close then use a cheap thermostat. If you're trying to learn how this stuff works then, by all means, dig in and start trying things. But what you're suggesting seems pretty expensive
for what you say you want.

MB

--
Michael R. Batchelor - Industrial Informatics, Inc.
Contribute to society: http://www.distributed.net/ogr/

 

Ge Fanuc has a PC based software product that will interface to hardware for sensing the temperature and controlling the heater or fan as a function of the logic you program in the PC. There is trending, alarming and other software components that you may use in your application. You may call me to discuss at 713-667-7200 ext 212.

Kerry L. Schrank
TriStar ECA

 

Sounds like you can do this with a simple on/off controller. Why don't you look at "www.omega.com":http://www.omega.com . Not the very top of the line stuff, but these guys do specialize in providing cost effective basic temperature controls to labs, universities, light industry and the like. They even have loads on information online about how to apply their controllers and sensors and have a pretty good tech support group. You can get everything you would need for a complete solution (sensor, controller, fan relay, heater relay, and heating elements) from them. If you are really unsure about how to proceed, then get help before you burn down the greenhouse.

 

Michael R. Batchelor:
> What's wrong with just using a commercial heating and cooling thermostat? <

Seconded. Depending on the temperatures you need, you might even be able to buy make use of ready-made stuff, like fishtank heaters from a pet
shop. Even if you can't, thermostats are pretty easy to wire up and cheap (easier than wiring everything up to a computer, anyway).

Another question is reliability - how precious is whatever's in the water bath? Your first attempt at control is unlikely to be that good (first attempts generally are that way).

If you need a record of the temperatures, wiring it up to a computer may make sense (you can put it on a webpage, then), but on the other hand
you might well make do with an off-the-shelf weather recording station.


Jiri
--
Jiri Baum <[email protected]> http://www.csse.monash.edu.au/~jirib
MAT LinuxPLC project --- http://mat.sf.net --- Machine Automation Tools

 

I think the previous answers are correct. You don't want to spend all your time trying to build a temperature control system. Neither you want to waste month analyzing data, only to find out it's all based on a faulty controller. I'd buy a complete system from one of the sources suggested ( "OMEGA.COM":http://www.omega.com is very good to college researchers) and get on to my research.

 

Hi

How can I ,using a pc running Labview Have a program that uses the onboard pc thermostat to control a relay to turn on an external extraction fan, using the serial port . Is this possible, Surely ???