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Calibration

Like anything in the real world, your sensors and devices won't necessarily work perfectly all the time. Many analog semiconductor devices are light, temperature, and pressure sensitive, so your actual readings can vary depending on outside conditions. Also, while sensors are usually manufactured to within pretty tight tolerances, every sensor has some finite error that you will need to account for to get maximum performance.

Some kind of calibration routine can help alleviate many of these concerns. By calibrating your sensors against a trusted source, you can correct a lot of the skew caused by outside conditions. Calibration will also eliminate any steady state error caused by the device itself.

A calibration routine collects a set of known data points and scales the input signal to fit the calibration data. Since we are calibrating a linear ADC, we only need two data points to determine its operating curve. To get the most out of the calibration, you should use two data points that are as far from each other as possible. In the case of the MSP430 G2231, that is 0v and 3.3v .

Calibration routine pseudocode (not in c syntax)

flag=0; interrupt function: calibrate()returns: lowMeasured, highMeasured {if flag=0: set low and set flag=1if flag=1: set highreturn }

Interrupts in c

Code Composer Studio has a special way of handling interrupts in C. It uses "compiler directives" (special instructions to the compiler, assembler, and linker) to specify which functions should go in the interrupt vector table. ISRs in C are written like any other function, except that they can take and return no values. This fits with the convention that ISRs don't interfere with or depend on the code around them.

Formatting an interrupt in code composer c

#pragma vector=PORT1_VECTOR //compiler directive saying that this function should correspond with the port1 interrupt vector__interrupt void interruptHandle() {//your ISR CODE }void main() {... all setup __enable_interrupt();//Enables general maskable interrupts ... the rest of your program}

Other concerns

Even though interrupts should work in isolation, you often need to get or modify data inside them. This can be done using volatile global variables. A global variable simply means a variable that any function in your code can see and modify. Using global variables is generally discouraged (they can be easily abused and lead to problems if you repeat common variable names), but in this case they allow you to interface with your ISR. Volatile is a directive that tells the processor to never cache the variable's value. When dealing with ISRs, cached variables could lead to problems if the ISR updates the cached data while another function is using it. Be careful using the volatile keyword excessively though-- the lack of caching slows down performance.

Full range voltmeter assignment details

Using Code Composer Studio 4, write a C language program to drive a precise 3 digit volt meter. Use the ADC to read the voltage and display back the actual voltage value. Write a calibration routine for your volt meter and an output routine that will allow you to display each of the output digits.

    Your program should include:

  • A setup section to setup the GPIO, configure the ADC, and enable interrupts
  • An ISR that runs the calibration routine and keeps track of what has been calibrated so far (so it will only run once)
  • A main loop that continuously samples, filters, and scales the ADC input to the 0-3.3 volt range as determined by your calibration.

Questions & Answers

what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
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?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
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?
Damian Reply
absolutely yes
Daniel
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Intro to computational engineering: elec 220 labs. OpenStax CNX. Mar 11, 2013 Download for free at http://cnx.org/content/col11405/1.2
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