# Eel3111 force sensor paper july 2010  (Page 2/3)

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Note the term pressure which means force per unit area. While advertised as a force sensor, in reality, the device actually is pressure sensitive. Testing has shown that the same 100 gram weight will cause a greater output voltage swing if the force is concentrated on a smaller area. Based on the above description it should be clear why. Localized high pressure on a given area of the sensor creates a very low resistance bridge between the enmeshed conductors at that point. Spreading the force over a larger area will decrease the resistance of the sensor as a whole but will not result in the very low resistance circuit created under high pressure.

## Operation

The 10 kilo-ohm resistor allows the circuit to act as a voltage divider. It also restricts the buildup of excessive current flow when pressure is exerted on the sensor. The equation for V out is shown below:

V out =

R FSR represents the sensor’s resistance under a given load. In this configuration the output voltage is very small when no load is applied. The voltage increases in a nonlinear fashion with respect to the applied load. This is due to the manner in which the resistance of the FSR changes with the applied load (See figure 4). Note that only as a substantial force is applied does the rate of change of resistance with respect to applied load move towards a constant value. Switching the positions of the two resistors would cause voltage to be at a maximum under no-load conditions.

## Ugb

As discussed above, V out is the voltage pickoff from the FSR network. This voltage is sent next to an op-amp that functions as a UGB. This is accomplished by connecting the output to the inverting input terminal [4]. No feedback resistor is used just a copper wire. This connection drives the gain of the amp towards unity and no amplification of the signal occurs. As discussed in class the purpose of this is to isolate the input to the microprocessor from the FSR circuit (fig. 5).

The op amp we used has the part number TLV2765. It was soldered directly on to the board. The rail voltages are 3.3 volts to the positive and ground (reference voltage) which is applied to the negative. This op amp is a rail-to rail op amp meaning that high fidelity can be achieved even when the input signal (V out ) is very close to one of the rail voltages [3]. This function is essential because under no-load conditions the input signal to the op-amp is very close to the reference voltage which acts as the negative rail voltage. In fact, during construction of the device we had to hook up multiple op amps before we could find one that was faithful under no load conditions. We could have dedicated a separate -3.3 volt supply to use as the negative rail voltage but selection of this op amp made that unnecessary. Full credit should be given to Mike Toth for solving this design problem.

## Msp430f449 and lcd

Up until this point in the circuit the signal representing the force applied was analog. The real magic takes place inside the microprocessor where the signal is converted in to a digital signal which is suitable for display on the LCD. Again we want to give credit to Mike Toth in the lab for doing most of the programming that was required. The MSP430F449 is a microcontroller unit complete with timers, analog to digital converters, and a LCD driver. It also contains memory which can be used to program the device to perform specific functions. The primary use for such a device is to capture analog signals, convert them to digital, and output the digital signal to an LCD or to some other device [2]. They can be purchased or procured as student samples at the Texas Instrument website. Figure six is a flow chart provided by Mike Toth that illustrates the flow of the program we used in this device. Notice the infinite loop (wait forever) and the one second interrupt. The infinite loop tells the program to execute a command with no predefined condition (that is not always true). Technically speaking this is like telling a program to run without ever giving it instructions on when to stop. This means that the only way to halt operation is to power down the device using the sliding switch on the front of the package. In C, the programming language used by engineers, there are different ways to exit an infinite loop. You can use the break command to end the cycle when a specific condition is encountered. Another method is to include in the program what is called an interrupt.

Is there any normative that regulates the use of silver nanoparticles?
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
why we need to study biomolecules, molecular biology in nanotechnology?
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
why?
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
what does nano mean?
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
it is a goid question and i want to know the answer as well
Maciej
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
what is fullerene does it is used to make bukky balls
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
so some one know about replacing silicon atom with phosphorous in semiconductors device?
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
for screen printed electrodes ?
SUYASH
What is lattice structure?
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
how did you get the value of 2000N.What calculations are needed to arrive at it
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