IR Thermopile circuit question

Hello,

I've salvaged a tiny IR sensor from an inexpensive hand held remote thermometer made by Cen-Tech; I got it from Harbor Freight. It's a great little device but I need to be able to send the output to an XBee BlueTooth-type transceiver, and thence to another BT transceiver, connected to a Linux laptop, via a USB port. Alternatively, I may use my Boarduino microprocessor and a TTL/USB converter cable to feed into the laptop.

Then, I need an active bar graph GUI app in order to show the change in temperature on the laptop screen. The whole idea is that I cannot use the tiny LCD readout on the handheld remote thermometer in the project I'm working on.

I have most stages of this already worked out except two key points: I will have to come up with the display GUI app, modify one, or learn how to write my own in C, or Java, or ?

More pressingly, I need to use the salvaged thermopile (I cannot identify mfgr, or anything else) in a home brew circuit. I've found several candidates after combing the Net for days, but no values are given for the components. I have some 741 and LM324 OP Amps and I'd like to be able to use them, if possible, especially the LM324 b/c it only takes a single voltage source. But if I have to, I'll get something else.

My thermopile has four leads in a tiny TO-5-shaped case, but it's only about 3-4 mm diameter. Before removing it from the commercial unit I measured voltages to identify the pins. Pin one, just clockwise from the index tab on the case, is V+, pin 2, still going clockwise, I think is the internal compensation resistor; pin 3 is V-, and pin 4 is electrically identical with the case.

I have posted a copy of one candidate circuit on Flickr, at: https://farm4.static.flickr.com/3032/2578992837_e32e910910_m.jpg

Thanks very much for your consideration and assistance.

Les Garwood

TCL- Tool Command Language will let you whip up a GUI in no time flat and has things like graphs and commucation libraries. Very easy to learn. Hardest part for me was figuring out how to actually compile the binaries after I downloaded it.

Thermopile project

Thanks very much for the prompt and helpful reply.

I am fiddling with the installation as I write this.

Until I get a circuit I can feel safe about using I'm kind of stalled in the wiring part of the project so at least I may get somewhere with the GUI aspect.

I do wish I could get some component values figured out for the circuit I have posted.

Thanks again

Les

What is the range of voltages generated by the thermopile? Were anything like R1 through R4 in the original circuit?

Forgot to add...

you want TCL and TK. TCL is the language and the logic. TK is the additional toolkit that makes everything GUI-ish and adds all the GUI stuff in.

Thermopile project

Mneary wrote:

mneary said:

What is the range of voltages generated by the thermopile? Were anything like R1 through R4 in the original circuit?

Click to expand...

I can't yet answer your question fully. I measured the voltages at the pins of the sensor before de-soldering it: at pin one, v+, I got 0.739, at pin two, I got 0.2 volts; this varied continually between 0.0 v and about 0.2 v every couple of seconds or less on my cheap DVM; on pin three, v-, I got 0.69, and on the case/gnd lead, pin four, I got 2.36 v., all relative to the closest thing I could identify on the PCB as a ground. Except for pin two, which I assume is the internal temp compensation thermistor, all other voltages were rock steady as far as I could tell. The original unit uses a single 2032 3V coin battery. I could not really tell what "mode" the unit was in b/c I had to dismantle the LCD readout in order to access the thermopile leads, but I tried stepping the mode switch several times and nothing changed at the pins while I did so.

As for R1 through R4, good question, but it's nearly impossible to trace or even visualize any discrete components on the tiny PCB.

Regards,

Les

ProfiLab can make a GUI and program it simple using signal processing blocks, It can interface to all sorts of hardware from COM ports to MIDI

Someone Electro said:

ProfiLab can make a GUI and program it simple using signal processing blocks, It can interface to all sorts of hardware from COM ports to MIDI

Click to expand...

. . .and is Windows-only, so DoctorLes would need to run it under wine or a vm on his Linux laptop.

TCL/Tk is a good choice, but there are also scads of other scripting languages which can do the same thing: PHP, Python, perl, really just about anything. Screenlets offers a framework built on Python and GTK+ which makes creating simple mini-applications stupidly easy.


Torben

Whops didn't notice it was Linux.