Public Lab Research note

Circuit diagram for simple thermal flashlight

by warren | December 12, 2011 05:40 | 15,396 views | 12 comments | #625 | 15,396 views | 12 comments | #625 12 Dec 05:40

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A redrawn diagram of the thermal flashlight posted by ad:

Parts list:

  • 1 Melexis MLX90614 non-contact IR thermometer (3v)
  • 1 RGB common-cathode LED
  • 2 4.7k Ohm resistors
  • 2 100 Ohm resistors
  • 1 180 Ohm resistor
  • 1 0.1 μF capacitor
  • wire
  • breadboard or circuit board & soldering eqmt.
  • Arduino
  • 9v battery and holder

Cost: ~$60

See examples of use:


Click this link to download the Arduino code for this project, posted by @shannon:

Files Size Uploaded
thermal-flashlight.fz 144 KB 2011-12-12 05:40:48 +0000
melexis.svg 2.67 KB 2011-12-12 22:31:43 +0000
melexis-pcb.svg 2.75 KB 2011-12-12 22:31:48 +0000
melexis-schematic.svg 2.18 KB 2011-12-12 22:31:56 +0000
melexis.png 10.9 KB 2011-12-12 22:32:01 +0000 15 KB 2011-12-18 21:14:18 +0000
melexis-90614.fzpz 16.5 KB 2011-12-19 13:33:32 +0000

I did this Help out by offering feedback!

People who did this (25)

Title Author Updated Likes
Finding Hotspots With Our Thermal Flashlight @FireLogCollective over 4 years ago
Thermal Flashlight: Tech Failure Spectacle @acnud over 4 years ago
Thermal flashlight: data collection in Holyrood, NL @ckenny over 4 years ago
KKMS Thermal Flashlight Project Sociology 4107 @KKMS over 4 years ago
Arduino Uno Thermo Flashlight Casing Specs @klrussell over 4 years ago
Comparison of Window Insulation in Old vs New buildings @weertsc over 4 years ago
Thermal Imaging of Northeastern University buildings @evanbjacobson over 4 years ago
Effective Cooling Methods In Refrigerators @tapetenttm over 4 years ago
Thermal Imaging of Fresh Air Intake for Nightingale Hall @jecnu over 4 years ago
Comparison of Heat Insulation in Two Different Aged Building using a Thermal Flashlight @AndrewConner over 4 years ago
Thermal Imaging: Heat Insulation Comparison @brachium over 4 years ago
Thermal imaging of Refrigerators and Milk @williammanning over 4 years ago
Thermal Imaging: A Comparison of Heat Insulation @fkamara over 4 years ago
Inexpensive Thermal Imaging of Decorative Lights in Household @NoorJandali over 4 years ago
Thermal Imaging: Heat Insulation in Older Building @SCG over 4 years ago
Thermal Flashlight Casing @SCG over 4 years ago
Thermal Imaging: Heat Insulation Comparison @SCG over 4 years ago
thermal flashlight env+tech_neu_2014 @iferrerb over 4 years ago
Thermal flashlight - ENV+TECH_NEU_2014 @JuliaR over 4 years ago
Test of the Thermal Light: Env+Tech_NEU2014 @jens over 4 years ago
Env+Tech_neu_2014 - Thermal Flashlight @hklebs over 4 years ago
Cheap Thermal Imaging Sensor @davidbanks over 5 years ago
Thermal Imaging Tests with Android Ap @sara almost 7 years ago
Thermal Images for Community Environmental College @sara almost 7 years ago
More thermal photography at Parts & Crafts @warren about 7 years ago
Show more


Illustration made in Fritzing (

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I've tweaked the code on the thermal flashlight a bit. In our testing, we were getting red for hot, but blue-green for cold (and figured 'blue' should be for the cold).

Here is a reference on how the color HSV (hue, saturation and value) converts to RGB:

Figure 24 shows the essence of what we are trying to do; 0 degrees = red; 240 degrees = blue.

The code in the sketch is almost correct; originally, the value was 360*0.6 = 216 degrees for the coldest value, which is blue-green. 240 degrees gives you blue, so you have:

// Regular ol' RGB LED: // original //int hue = map(state,0,255,(360.00*0.60),0); // not the whole color wheel // // 0 degrees is red, 240 degrees is blue // See // Figure 24. // 0=cold is 240 degrees (blue) // 255=hot is 0 degrees (red) int hue = map(state,0,255,240,0);

setLedColorHSV(hue,1,1); //We are using Saturation and Value constant at 1

The other part of the code that will have to change is that if you use a common anode RGB LED (the LED from RadioShack is 276-0028 (common anode (+), which is at 5V), when the PWM output is at 255 for a particular color (5V is on all the time), that color in the LED will be off. So we have to invert the output (zero becomes 255, 255 becomes zero):

// Since we are using common anode, when value is 255 (on always) // the LED for that element is OFF, so, make a swap setLedColor(255-red,255-green,255-blue);

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Thank you very much for this circuit.

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Has anyone built this circuit with the BlinkM MaxM? If so, could you please explain how you connect it to the Arduino? On the diagram above I see the PWM pins are used for the led, but since the BlinkM MaxM got built in PWM I guess this won't work? Is it possible to just disconnect the Master board and use the Blaster led cluster alone, connected to the PWM pins on the Arduino like in the diagram? :O

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I've been trying to figure out the MaxM here:

not a lot of progress just yet. Kyle from NYC managed it, but I haven't been able to unravel his code yet.

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I have just built a test unit of this, seems to be working well.

For the moment I have the colouring scaled from pink, through blue, cyan, green, yellow, orange, red and finally purple. Currently have all of that set using intervals of the temperature (10-30oC), but might see if I can get that into an equation format (may be a sinusoidal one?) to make it a bit more flexible and configurable. Saw something that someone has already written somewhere to do this, so going to check that out.

I plan to add two switches on it, one that will change the lowest temperature and a second that changes the total temperature range. That should make it a bit more flexible for use.

Got rid of all that silly oF from the program too ;-), now just in oC, makes much more sense :-)

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Hmm, may be yours above does something similar already?

Don't really understand the code, not my strong point, will have to have a play and see ....

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Now have my program fully working, seems to do what I want it to do.

Issue now is the fact that the 3 colour LED doesn't mix fully, if you have all three on then you have distinct spots of red, blue and green. Looking around now for a lens that will mix them correctly, so that get the actual colour over the entire area, rather than just where the three colours happen to mix.

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Jeff, not sure how to reply to your message, where is the message / contact panel here?

Anyway, I will definitely putting it up here to share with others.

At the moment it is mostly just the coding. I have worked out the formula to do the colour mapping for the range purple to pink (did that in Excel), just have to get that into the programming language so that it works. Basically it is the colour wheel, from 300o for the coldest, then as the temperature increases it goes around the wheel of decreasing angle, through zero and to 330o for the hottest temperature. Working off the following image

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just awesome... but i'm little confused, how many LED you used?

-Shuvojit Das

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Sorry folks, i hadn't been getting email updates for these comments; I will now though!

I'm trying to adapt the Visualight to do this, much smaller:

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Greetings from Barn Raising 2014. Live from Lumcon! We just finished a wonderful workshop on this tool, and there was a bit of a kerfuffle (slightly over dramatic) surrounding the file downloads. The links on this page to download files from buldr are not working for me (they work for others). We've created a folder that has all of the files in one place on the wiki page: I think it would be worth putting a link at the top of this page to the wiki which can be the place for the most up to date files/links etc.

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