Wrist-Worn Fever Alarm

Monitor your (or a loved one's) body temperature, with a notification should it reach fever level.

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The COVID-19 pandemic has many of us concerned for our health. This semi-wearable device can unobtrusively monitor your body temperature, or that of a loved one, and alert you if it reaches fever level.

While the pandemic was the inspiration for this project, it could also be used to monitor body temperature for ovulation cycle, to check for fever in an infection-prone loved one (especially one who is elderly or non-verbal autistic), or any number of other matters.

 Preliminary Details

The following preliminary sketch details assume the product is a wristwatch-style package. Therefore some of it may not be relavant to the final product

Lowest possible component count / energy consumption. Run off two LR44 alkaline button cells.  Microcontroller based whatever's easiest and familiar to use i.e. ESP32 . Temperature sensor a bead thermistor. Piezo electric transducer with series inductor. Dual color LED. A few Resistors. Reed switch sensor. Development model may have added uC programming interface.

Worn on body, quietly monitoring. Touch magnet at any time (if curious) to reed sensor to interrogate temperature. LED signals series of flashes. 

Operation: Circuit spends most time asleep drawing a few microamps running sleep timer.   Half hour timeout wakes uC from sleep.  Energises thermistor bias for whatever microseconds needed to read it, does some maths, then goes back to sleep for another 30 mins.  Maths includes an algorithim to analyse average temperature and to look out for increase in temperature.  An alarm is a beeping from sounder with a simultaneous flash. Red for over, Blue for under.  Alarm silenced (snoozed) by magnet touch to reed sensor. 

Holding magnet to reed sensor for 10 seconds turns unit off/on and resets alarm. On/off is confirmed by beeps/ flashes. 

Optional: LED could output a dump of recorded data as RS232 style serial on demand. Possible read non-contact with photodiode linked to a serial data USB module. Could omit the LEDs and just have code of beeps instead.

Software ideas: Clock speed expected < 100 kHz. Timer running during sleep rollover triggers wake up, i.e. through interrupt.  ADC switched off to save power during sleep and turned on to measure temp sensor. Use a digital IO set logic high to energise and supply temp sensor circuit. Some means of ADC compensated measurement required to cancel effect of battery voltage change. Digital IO directly drives piezo transducer via inductor to boost audio level. Signalling of data requested by beeps/flashes 'three, six, three' to indicate 36.3.    

Design Details

The current design satisfies the "lowest possible component count" requirement. It uses a Feather system, with a main board (Adafruit HUZZAH32 - ESP32 Feather), another board for a display, a DS3231 Precision RTC FeatherWing (for a real-time clock), and a proto Wing to connect the two temperature sensors. These should allow the system to be small enough that a wristwatch-style enclosure can be designed.

Some experimentation will be needed to determine how long the battery will last on a single charge.

For the alarm itself, the HUZZAH32 features both BLE and Wi-Fi, so an alert can be sent to a smartphone or computer. Giving the device its own sound capability (per the preliminaries) will be TBD.

Rather than a reed sensor, this design uses a simple push-button to reset the alarm. The temperature can show any time on the display. Since the device is to be worn like a wristwatch, the time is also on display.

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Arduino based Heartbeat and Body Temperature Monitoring IoT Device

  • 1 × Adafruit HUZZAH32 - ESP32 Feather Main processor board. Provides basic processing, plus BLE and Wi-Fi.
  • 1 × Adafruit FeatherWing OLED - 128x32 OLED Add-on For Feather Display to show temperature
  • 1 × CR1220 12mm coin cell Lithium Ion battery for the RTC
  • 1 × Adafruit FeatherWing Proto For attaching the sensor(s)
  • 1 × 3-pin female right-angle header For plugging in the pulse sensor (below)

View all 11 components

  • 1
    Assemble the Proto Board

    The components on the Proto Board should be assembled as shown below.

    The guide to wire colors:

    • Grey "wires" are solder bridges.
    • The brown wire should be run on the underside of the board.
    • The blue, black, and red wires should be run on the top.

    Put them on in that order (though the actual wire colors are up to you) before adding the other parts.

    The other three components can then be added in any order, but be sure that:

    • Pin 1 of the sensor is at the "south" end, so it connects to the 3V bus.
    • The right-angle headers are pointed toward the outer end.
    • The Picoblade is also pointed toward the outside.

    You can ignore the last two if you want to for some reason, but if you get the first one wrong the device won't work properly (if at all).

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Marcrbarker wrote 04/17/2020 at 00:48 point

Hi Just checking in to see. How's it going?   

I've just had look at the ESP32 tech data. Way too much a learning curve for me at my time of life, I'll pass!    

While I'd looked through the 681 pages though I see ESP32 power consumption is 200 mA in active mode but can drop to 800 uA while running its 8 MHz ULP co-processor. The ULP seems capable of doing a lot without needing invoke the full CPU.   

  Are you sure? yes | no

bobgreenwade wrote 04/17/2020 at 01:12 point

I have enough figured to put together the hardware. I just need to acquire said hardware. I have a cart at Adafruit full of stuff (for both that and my SoundWing/EchoWing projects) but they're not shipping anything until New York is no longer on lockdown. I may see if someone else has the specific items for this project and get them there, though.

I don't think the ESP32 tech data will be a big deal, for the most part. Once all the hardware is deemed compatible and correctly wired, it'll just be a matter of programming the thing and working out an enclosure.

  Are you sure? yes | no

Marcrbarker wrote 04/17/2020 at 01:30 point

:-)  "..a matter of programming.. "  That's just what I find quite scary!

  Are you sure? yes | no

Marcrbarker wrote 04/06/2020 at 15:38 point

Ah! Having seen the components just added (LCD display, IR sensor etc), these details I've just added I don't think are going to be any help.  The details I'd added are for a very much simpler device that runs for many weeks on two LR44s.  You might want to remove these details I added or use utilise for something else.  

  Are you sure? yes | no

bobgreenwade wrote 04/06/2020 at 16:27 point

I can go edit the Details later, if you don't beat me to it.

(I'm waiting in case I come up with a good way to do this with LilyPad instead of Feather.)

  Are you sure? yes | no

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