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Remote thermometer question
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Remote thermometer question

by DoctorLes on Thu May 15, 2008 12:06 am

Hello,

I have a small, cheap, commercial hand-held electronic thermometer that senses from a distance--no direct contact used. It has a small LCD readout screen graduated into 0.1 degree F increments; it responds quickly to temp changes.

What I very much want to do is hack this thing to either use the sensor in it, or the whole device, to input to my boarduino. I want to then be able to send the output of my boarduino to a PC via a USB cable or to a blue tooth unit so I can go wireless to the PC.

I want the PC to make a graphical screen display of the thermometer's temp changes via either a pre-existing software app, or one I can hack to do it, or write myself if necessary.

What I'm asking is this: if I use just the thermometer's sensor (looks like a tiny silver auto headlamp cone) what input port type would I likely have to use on the boaruino? What type of modifications to it might I be looking at having to make?

If I just use the whole thermometer, what kind of things do I need to do to get its output coupled to my boarduino, would I find the input to the LCD readout or do I need to go further upstream to find the input to the LCD driver circuits, or what? Would this be more or less practical compared to just using the sensor?

Thanks for your time and consideration

Regards,

Les :?:
Free Will is a compelling but dangerous illusion. Visit naturalism.org for more info.
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by Silver on Thu May 15, 2008 3:25 am

Hi Les,

If the electronic thermometer that senses from a distance is similar to the cen-tech IR thermometer ($9.99 from Harbor Freight), I don't think it would be easy to connect it to the arduino/boarduino. Trying to find a connection inside that would give you access to the temperature or trying to decode the display would be a lot of work.

The IR thermometer has both a room temperature reading and a sample reading, so you might be able to get just the room temp for your logging, but it says the battery is only good for 40 hours of continuous sample reading, so you be limited to two days if you lock the IR sensor into continuous sample mode.

My suggestion would be to purchase an inexpensive LM35 precision temperature sensor for about $1.75 and connect it to your boardino. The LM35 is about the size of an LED or it comes in a form that looks like a voltage regulator that can be connected to a surface to provide a surface temperature. See this thread http://forums.ladyada.net/viewtopic.php?t=5763 for sample code and instructions.

You could take a reading each minute and place the results into an array. This would need about 1440 bytes of data for a full day of data. Connect a simple switch to a digital input and check its level every 10 seconds or so. If the switch goes high, you can send the contents of the array out on the serial connection. If the switch is held for three consecutive checks, you can reset the array counter back to zero and start the collection process over again.

Silver
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Remote Temp Sensor

by DoctorLes on Thu May 15, 2008 10:22 am

Hello Silver,

First, thank you VERY much for your prompt and helpful reply; it's just what I wanted to know before spending time on this project.

And yes, it is the Cen-Tech IR thermometer device from Harbor Freight. I need a remote, non-surface mounted device that can scan/sample an area about 10 cm in diameter, give or take 50%, but not just a single point. Also, direct contact may introduce spurious data for my intended application and would be hard to manage technically. So, I looked at the LM35 but am deferring it for now b/c of my need for a remote sensor.

Given that this is an IR device, with an almost certainly analog output, can you tell me if I can directly couple it to an analog input gate on the Boarduino? Do you think this is a variable resistor sensor or a voltage generating device? That info would help. Of course, I'll likely just tear into it and see, but it may help to know in advance.

Regards, and Thanks Again

Les
Free Will is a compelling but dangerous illusion. Visit naturalism.org for more info.
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by macegr on Thu May 15, 2008 3:16 pm

If a contact device is still a possible option, the MAX6675 is a very easy to use thermocouple amplifier and ADC device. It's a little expensive, but so painless to use. Here's one source of the chip: http://www.sparkfun.com/commerce/product_info.php?products_id=307
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Thermopile is operational!

by DoctorLes on Sat Jul 05, 2008 9:06 pm

OK, in case you are interested, I am successful making the salvaged thermopile work with my boarduino. I'm still jazzed about that but the next hurdle is making or obtaining a practical, computer-side display of the temperature output.

Right now, I have output going from my boarduino to the TTL/USB cable, into my Linux/Kubuntu laptop. I get a rapidly changing numeric readout in degrees. I'm using Silver's code for this, and it works well, but . . .

I really want a dynamic bar graph, perhaps with added audible tone and color changes, but that's not critical. And, as a minimum, I really need a very large bar graph or some other graphic display of the temperature as it changes in REAL TIME.

I've spent many hours searching for some open source code I could adapt in some way. I'm willing to try to write my own in, say, "Processing", but I'll have to get a book on it and start from scratch. I was hoping to not have to reinvent the wheel, however.

Does anyone know where to find libraries of open source code I might adapt for my project?

BTW, thanks for your code, Silver, it helped me get this far!

Regards,

Les
Free Will is a compelling but dangerous illusion. Visit naturalism.org for more info.
DoctorLes
 
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Please be positive and constructive with your questions and comments.