week 6

Due to the load cell sensor cannot use anymore,I change my sensor.The suitable sensor is Flexiforce sensor.

What is Flexiforce sensor?

Figure 1: Flexiforce sensor.

figure 2: structure of flexiforce sensor

Figure 3: small size of flexiforce

Figure 4: another size of flexiforce

References
 http://www.prweb.com/releases/zif-compatible/flexiforce/prweb4192224.htm

http://www.c-stamp.com/CS497000.htm

week 5

Activity : Testing circuit with load cell sensor

Component or equipment: load cell sensor,trainer,resistor 1kohm,multimeter

Result: By using wheatstone bridge circuit, the load cell not successfully produce the fix range. Beside that, the non- stability were result. The range is not stable.

Conclusion : The load cell sensor have 2 strain gauge.So that, when the force applied to the sensor, the range is not stabilize. Cannot produce fix rate. Moreover, the load cell sensor is not suitable to the mouth.

week 4

wheatstone bridge ??

Why I'm talking about 'Wheatstone bridge'?because this relate with my circuit and load cell sensor.

 Wheatstone Bridge is a device for measuring electrical resistance. When the bridge is connected in an electrical circuit, part of the current flows to the object whose resistance is unknown, and part flows to the resistor of known resistance. If more current flows through one side of the circuit than the other, the galvanometer shows the difference. The sliding contact is then moved along the wire until current flows equally along both sides of the bridge and the galvanometer shows zero.

 When the bridge is thus balanced, the unknown resistance is calculated by a formula. The formula is: X = RD'/D (X is the unknown resistance. R is the known resistance. D is the distance from the key to the right end of the meter stick. D' is the distance from the key to the left end.)

more information,visit these website
http://www.play-hookey.com/dc_theory/wheatstone_bridge.html
http://www.absorblearning.com/advancedphysics/demo/units/020202.html
http://www.citycollegiate.com/wheatstone_bridge.htm
http://www.cs.cmu.edu/~dst/E-Meter/wheatstone.html

Video about wheatsone bridge

week 3

Strain gauge has related with load cell sensor.The strain gauge has been in use for many years and fundamental for any other sensor such as pressure sensor and etc.

 When external forces are applied to a stationary object, stress and strain are the result. Stress is defined as the object's internal resisting forces, and strain is defined as the displacement and deformation that occur.

 Strain may be compressive or tensile and is typically measured by strain gages. It was Lord Kelvin who first reported in 1856 that metallic conductors subjected to mechanical strain exhibit a change in their electrical resistance. This phenomenon was first put to practical use in the 1930s.
Figure above is define as stress and strain.

Visit a few website to get knowledgeable about strain gauge.
http://www.sensorland.com/HowPage002.html 
http://www.omega.com/literature/transactions/volume3/strain.html 
http://www.dynasen.com/html/stressstraingages.html 

week 2

I'm still in research about my project. I have to change my previous sensor that is FSR sensor,to load cell sensor. FSR sensor having problem to get precision measurement. So, I try to test with this load cell sensor.I buy load cell sensor at Jalan Pasar,Kuala Lumpur with RM55.00.

Figure above is load cell sensor.Have 4 different colour of wires. This is web that content the datasheet and specification of load cell sensor,http://www.phidgets.com/products.php?product_id=3133_0

week 1(fyp 2)

Assalamualaikum and welcome to the S2'2012. So, this semester become fyp 2.More information I will update on this semester regarding the process of my project.'mouth assessment'.

For this week I want to present about load cell sensor.

 Load cell is the transducer that is used to convert force into electrical signal. As compare to FSR(force sensing resistor), the load cell sensor suitable to get precision measurement.

figure above is hardware install.

For more information about load cell sensor visit this webwww.sensorland.com/HowPage005.html

week 14

More about FSR
FSR pro’s and con’s:

FSRs are just resistors, so they are easy to work into circuits, and sometimes don’t require any support circuitry. They are also relatively inexpensive and readily available, even Digikey has started carrying the Interlink FSRs. But, unfortunately, that is where the pro’s end. The main drawback to FSRs is a result of its central component – the spongey resistive material in the middle. Just like a sponge, it takes a while to re-inflate after its been compressed. And worse yet, this re-inflation time is a function of how long and how hard you pressed on it.  After you release, the FSR value will come back to 95% of its initial value almost instantly, and then drift that final 5% over the next 10 seconds.

The inner material is also very sensitive to how it is pressed. It has a non-linear pressure response which varies with time, temperature, humidity, and even between parts of the same production batch. This makes the FSR a poor choice where accuracy and repeatability are a concern, especially across many units. Fortunately, a lot of musical applications have a human in the feedback loop who is able to just press harder or softer to get the desired effect, making this inaccuracy of less concern.

Finally, FSRs can also be very fragile. They are made of thin, laminated plastics, and are frequently placed under high forces.

Which FSR should I use?

The main two manufacturers of FSR sensors are Interlink and FlexiForce. Interlink FSRs come in a wide range of shapes, are relatively inexpensive, and fairly robust. On the downside, they vary greatly between units, have a lot of resistance drift over time, and are a bit slow to respond. The FlexiForce sensors, on the other hand, tend to be more accurate and repeatable, but are more expensive and fragile. In applications where exact forces don’t need to be measured, the Interlink products will probably serve you best. For more repeatable results, the FlexiForce sensors will be better (as they rely on the piezoresistive effect). But, if you really need consistent results, an FSR isn’t the best choice, and a load-cell or strain guage should be used.

more details at http://www.openmusiclabs.com/learning/sensors/fsr/