SafeTouch Temperature Sensor
Olivier Musca, Rachel Andersen, and Matthew
Tessier
The goal of our project is to develop a heat
sensing device which could be implemented in an artificial limb
to alert the user when their prosthetic is in contact with a
heat source capable of damaging his or her prosthetic. The
purpose of wearing prosthetic limb is to allow the user to have
the independence that may not have due to missing limbs. Such
independence is exemplified in everyday tasks such as cooking
meals. A task like this introduces opportunities for damage to
the arm from high temperature sources such as stove tops, ovens
and any other cooking equipment.
By nature the robotics in the latest prosthetic
technology, these devices can be highly sensitive to heat, as
well was very expensive to repair or replace, Since the wearer
of a prosthetic cannot feel heat in the absent extremity, it
becomes essential to provide a warning system when critical
temperatures have been reached.
While we are emphasizing the safety of the
prosthetic, it is important, it is important to realize that
damage to the prosthetic, although undesirable, is preferred to
injury to the person. This quality suggests that the warning
system itself should never place the wearer's person in danger,
which translates to a passive warning system., such as a buzzer
or a light, as opposed to a physical motion of the arm moving
away from the heat source. This is why SafeTouch chose to use
both the buzzer and the LED alerts.
Many designs for heat sensors include several
components which, in the space allotted by a prosthetic, seem
large and unnecessary. Safetouch has simplified the design for
cost effectiveness and to adhere to spatial constraints. Our
final design does away with potential problems inherent in the
potentiometer and the bulkiness of the relay. Vibrations and
other movement that prosthetics are more than likely to
encounter could cause the screw adjustment of the
potentiometer to turn in time and throw off the calibration and
therefore the sensitivity of the sensor. Furthermore, it is
undesirable to have an inexperienced user self-adjusting the
temperature threshold as this setting should be as specified by
the prosthetic manufacturer.
The temperature sensitive component in the
SafeTouch system is the thermistor. The thermistor is
essentially a resistor whose resistance decreases with
increasing temperature.
An operational amplifier is used as a comparator.
Using resistors and the thermistor as voltage dividers, the
voltage input from the positive side will exceed the input of
the negative side of the amplifier when the resistance of the
thermistor reaches a specified temperature. When this happens,
the output voltage of the amplifier will jump from close to zero
to close to the power supply voltage, allowing enough voltage
for the LED and buzzer to turn on. In other words, when the
thermistor is heated to a critical temperature, the alert will
be set off.
The SafeTouch system is a simple and cost effect
way to protect costly prosthetics from damage due to extreme
heat. This project was done in the hopes of helping those whose
independence relies on the use of prosthetic limbs.
