Building An IR Thermometer That Fits On Your Keychain

Non-contact infrared (IR) thermometers used to be something of an exotic tool, but thanks at least in part due to the COVID-19 pandemic, they’re now the sort of thing you see hanging up near the grocery store checkout as a cheap impulse buy. Demand pushed up production, and the economies of scale did the test. Now the devices, and the sensors within them, are cheap enough for us hackers to play with.

The end result is that we now have projects like this ultra compact IR thermometer from [gokux]. With just a handful of components, some code to glue it all together, and a 3D printed enclosure to wrap it all up, you’ve got a legitimately useful tool that’s small enough to replace that lucky rabbit’s foot you’ve got on your keys.

If this project looks familiar, it’s because the whole thing is closely related to the LiDAR rangefinder [gokux] put together last month. It shares the same Seeed Studio XIAO  ESP32-C3 microcontroller, 0.49 inch OLED display, and tiny 40 mAh LiPo battery. The only thing that’s really changed, aside from the adjustments necessary to the 3D printed enclosure, is that the LiDAR sensor was replaced with a MLX90614 IR temperature sensor.

[gokux] has put together some great documentation for this build, making it easy for others to recreate and remix on their own. Assembly is particularly straightforward thanks to the fact that both the display and temperature sensor communicate with the ESP32 over I2C, allowing them to be wired daisy chain style — there’s no need for even a scrap of perfboard inside the case, let alone a custom board.

11 thoughts on “Building An IR Thermometer That Fits On Your Keychain

    1. Yeah, the builds are so similar that I’m guessing gokux just copy/pasted stuff like the parts list and forgot to change that line. The rest of the info on the page and the source code properly references the MLX sensor.

  1. Keychain IR thermometer would be very useful. Most “guns” are still big and sometimes you just need to test something before you touch or test if equipment is hotter than usual. Very cool idea.

  2. These are fantastically useful tools.
    And you can even buy one at Harbor Freight for $5. (or could, ten years ago). Harbor Fright catalog number 93983. “Pittsburgh Non Contact Pocket Thermometer” Mine also has the “CEN-TECH” brand on it.

    I liked it so much I went back the next day and bought another. Multi function: As well as the usual temperature peak hold function, it has a clock, timer, stopwatch function. With the clock operational it eats a CR2032 every few months. With the clock disabled the battery lasts years of daily use.

    1. I have one of those in my backpack 🎒.
      2 things I don’t like about it.
      The battery cover is loose.
      Or the battery is often dead when I need it.

  3. ESP32 for me seems like an overkill for a task like that. Something like ATtiny13 could do. But yeah, if you don’t want to sell your product – you can even take an stm32f407zgt :D

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