Wristwatch Temperature Monitor with Visual Alarm

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The CDC recently estimated that there are 83 million nosocomial (hospital-acquired) infections a year. The majority, 52.8%, resulting in pneumonia. Pneumonia is caused by bacteria, viral, chemical or other microorganisms. The majority of times the patient responds by spiking a temperature. Temperatures are normally taken once to three times a day.

Constantly monitoring of temperature adds another tool to our arsenal. This watch, designed to be disposable, monitors the patient’s temperature every 8 seconds.

The body core temperature is often measured with an oral thermometer and the average appears to be 98.6 oF. (37oC). It has been determined that skin temperature is lower by an emissivity correction of .95.

First, to test the principle, I built a recording SD card Wrist Watch temperature to validate the reported findings and monitored my temperature for a week once per minute.

The watch that followed that I designed is an inexpensive Go, borderline, No-Go LED indicator temperature monitor. It has 8 electronic parts + Heatsink, watchcase, board and battery. Cost estimate $4.00 each.

Sometimes temperatures spike for a few minutes and return to normal. I added an algorithm that if the temperature is above 100oF for 5 minutes without going green it will lock and blink double red. When a nurse or the patient sees a blinking red indicator, it indicates that he or she has spiked a temperature for over five minutes. The watch is reset by using a magnet and passing it over the top or bottom of the case.

It uses a TO- 92-3 LMT86LP with an accuracy of +/-0.2C for the sensor. The temperature sensor is imbedded in a washer about the size of a quarter which acts as a heat sink.

The output from the sensor is fed into a microprocessor with a 10-bit a/d converter.

The firmware takes the voltage of the sensor and determines how the LED is to be lit using its A/D function. It uses a bi-colored LED displaying green, red or multiplexing it for the color of orange-yellow.

It is powered by a lithium battery.

The above watch was designed to be the most economical with only a visual indicator. By increasing cost, it can be modified to:

  1. A vibration annunciator for patient touch sensory detection.
  2. An oral alarm.
  3. Using Wi Fi or BlueTooth to transmit to the nurses’ station an alarm with the patient’s room and bed number indicating temperature rise.

The watch can be easily be produced as all components are mounted to circuit board including the battery. It is designed to be used in a hospital on every patient. It has a special application for a patient in recovery after anesthesia.

This watch provides more efficiency to nursing, quality of healthcare to the patient, lessens liability to the hospital, and can save lives.

Schematic, Firmware, BOM and construction protocols available by request.


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  • Name:
    Ronald Newton
  • Type of entry:
  • Profession:
  • Ronald is inspired by:
    Providing medical devices at very low cost especially to developing countries. My travels to Africa, South America, Russia and teaching Bio-engineering to students. I have degrees in chemistry, electronics and was licensed as a "Clinical Laboratory Scientist". 84 years young.
  • Software used for this entry:
    Microchip, Eagle
  • Patent status: