An intelligent clinical thermometer that can distinguish between colds and flu

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Flu can lead to complications, some of which can even be life-threatening without treatment: Inflammations of the throat, paranasal sinuses and middle ear and finally even pneumonia or myocarditis are possible. Such complications do not occur with colds. As a result, 646,000 people die of influenza every year worldwide. The fatal thing is that flu is often confused with the harmless common cold. This is not surprising if one considers the symptoms: Even if the viruses behind them are different, distinguishing between flu and colds on the basis of the signs of the disease can sometimes be difficult even for doctors. This is because the symptoms are similar. Nevertheless, there are small differences that can indicate whether it is a flu or a cold, even without pathogen detection.

Especially my 8 year old daughter has often fever due to the daily contact with other kids. Mostly fever starts on weekends, so that our pediatrician is not available and we as parents wonder if she has caught a cold or a flu. It is indeed possible to be vaccinated against influenza, but as influenza viruses can change very quickly, the vaccines have to be adapted each year to the influenza viruses that are likely to be most prevalent in the next flu season and it is necessary to repeat the vaccination before each flu season with the current vaccine. So there is never a 100% protection. Healthy children or teenagers are normally not vaccinated at all. And some people can't or won't get vaccinated. So one day I had the idea to design a clinical thermometer that can distinguish between cold and flu...and maybe later diagnose other diseases for example caused by the 2019 novel coronavirus etc.

F°LUEX uses a naive Bayesian classifier, which is commonly used in automatic medical diagnosis. After taking the body temperature, the thermometer asks a few questions about the symptoms and then calculates the probability of whether it is more likely to be a flu or a cold. F°LUEX can be used as ear or a temporal artery thermometer, as this type can be used even while a child is asleep. It is powered by two 1.5 V AA alkaline batteries, has a small OLED display, a soft power switch and a miniature joystick for navigation. It is controlled by a Teensy 3.2. The temperature sensor is a Melexis infrared thermometer with 3V medical accuracy and 5° FOV. All electronic components are on one PCB. I made sure to use as few as possible and only easily obtainable standard components. The two-shell housing is 3-D printed in versatile plastic and sandblasted afterwards. I wanted a straightforward, industrial design to stand out from the usual design forms of clinical thermometers. Two first renderings follow. Further details of the project can be found in the corresponding logs.

This project is released under the MIT license.


Datasheet of the MLX90614 infrared thermometer

Adobe Portable Document Format - 2.70 MB - 02/13/2020 at 15:21



Datasheet of the tantal capacitors used for the LT1300 circutry

Adobe Portable Document Format - 1.35 MB - 02/13/2020 at 15:20



Datasheet of the p-channel mosfet DMG3415U

Adobe Portable Document Format - 572.24 kB - 02/13/2020 at 15:20



Datasheet of the miniature joystick

Adobe Portable Document Format - 144.63 kB - 02/13/2020 at 15:20



Datasheet of the used inductor for the LT1300 circutry

Adobe Portable Document Format - 194.45 kB - 02/13/2020 at 15:20


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  • Schematic and PCP design

    M. Bindhammer3 days ago 0 comments

    As usual I start with the creation of the schematic for a project. As already mentioned that the circuit is powered by two 1.5 V alkaline batteries. The LT1300 forms with L1, D1, C2 and C3 a 5V step-up converter. The 5V output voltage is guaranteed to a minimum input voltage of 1.8V. The 5V are then feeded into the Teensy.

    Q1, R3 and SW1 form a simple latching style power circuit. On power up the R3 resistor pulls up the gate on the U1 p-channel mosfet which prevents current from flowing through U1. When the user presses SW1, the gate on U1 gets pulled to ground which allows the current to flow, the LT1300 and the Teensy turn on. The Teensy then drives the GPIO pin to ground. When the user releases SW1 the GPIO pin keeps the gate low. The Teensy (or user) then just Hi-Zs the GPIO pin when it needs to shutdown. This way it can make sure the data is safe when it shuts down.

    Resistors R4 and R5 are wired as voltage divider to monitor the battery voltage. R1 and R2 are pullup resistors for the I2C bus, R6 to R10 are pullup resistors for the miniature joystick. PZ1 serves as an acoustic signal generator. BAT1 feeds the internal RTC of the Teensy. For this purpose a 32.768 kHz crystal must be soldered to the bottom of the Teensy board, for details see here.

    Since we're going to be powereing the Teensy from the 5V step-up converter, we want to cut the jumper that bridges the USB bus voltage to the Teensy power input.

    I designed the PCB  layout with Fritzing. The board has a custom shape. For this I used Inkscape - an excellent tutorial can be found here. As usual I routed the PCB by hand. And as usual I am using AISLER to manufacture the board. They are quick, cheap and very reliable.

    Top layer rendering:

    Bottom layer rendering:

    Before the housing can be designed, a 3-D model of the populated board is required. I use Sketchup for 3-D modeling.

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