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 Author Topic: Some questions I had on my project.  (Read 425 times) 0 Members and 1 Guest are viewing this topic.
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 « on: December 04, 2011, 02:59:50 pm » Bigger Smaller Reset

Hello,

I’m a student industrial engineering (electro mechanics) who has to design a measurement device as a Masterproject. This project is actually better suited for engineers in electronics so I’m totally new with ardruino and the the technique.
So in my project I have to measure the distance between a turbine blade and the housing of the turbine when the turbine is spinning with a low speed. I wanted my machine to sent the data to a Smartphone by using a bluetooth connection. In the Smartphone we will make an app to get the average distance, maximum distance, etc.
We are using a linear inductive sensor because this is the only one who can do our job in the right conditions. A linear inductive sensor has an analog voltage output from 0 to 10V. I wanted my arduino board to change this data in millimeters and sent this data to a Smartphone. Our accuracy has to be 0.05mm. I know this is possible because I already saw some examples, but I actually still have some questions about this project.

• The blue tooth board has a 115200 baud rate. One analog number has a size of 10 bits which has to be sent from the arduino board to the Smartphone. The 10 bits packages have to start and end with a start and stop-code, so I’m guessing a package of 14 bits will do. So actually if these approximations are correct I can sent the numbers with a speed of 115200/14= 8228 analog numbers per second. Is this correct?
I can imagine that the connection with the Smartphone has a lower baud rate, or does this only depend from the board? I have to be able to sent a analog number (in mm) every 0,02 seconds.
• The blue tooth board has a 115200 baud rate. One analog number has a size of 10 bits which has to be sent from the arduino board to the Smartphone. The 10 bits packages have to start and end with a start and stop-code, so I’m guessing a package of 14 bits will do. So actually if these approximations are correct I can sent the numbers with a speed of 115200/14= 8228 analog numbers per second. Is this correct?
I can imagine that the connection with the Smartphone has a lower baud rate, or does this only depend from the board? I have to be able to sent a analog number (in mm) every 0,02 seconds.

Our sensor has a maximum output of 10V, this voltage will change if the blade gets closer. The arduino boards can only take 5V. I was thinking of a solution to change the voltage from 10V to 5V. You can see it on the figure I made.

R1=R2, the sensor is a dc sensor which produces maximum 10V(=the batery icon) . So there is going to be 5V over R1 and 5V over R2. At the analog input (A0) I can measure the 5V. So I always divide the voltage into 2. But I think my accuracy is also divided by 2. Is this correct? Do you guys have a better solution for this problem?

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I don't think you connected the grounds, Dave.
 « Reply #1 on: December 04, 2011, 03:11:54 pm » Bigger Smaller Reset

Typically, for any  serial link, you'll be limited to eight bit packets, so nine bits of data will result in twenty bit periods of air time.
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 « Reply #2 on: December 04, 2011, 03:37:20 pm » Bigger Smaller Reset

You should be able to use a simple pot as a voltage devider to make the sensor output 0-5v. Not sure for the high rate of measuremrnt unless you are trying to measure for each blade, which would require each blade to be individually identifiable.
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 « Reply #3 on: December 04, 2011, 03:55:56 pm » Bigger Smaller Reset

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So in my project I have to measure the distance between a turbine blade and the housing of the turbine when the turbine is spinning with a low speed.

If that is your project why are you spending so much time thinking about sending data over bluetooth, do you get any points for that?

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 « Reply #4 on: December 05, 2011, 07:34:24 am » Bigger Smaller Reset

What is the range of measurements your sensor can make?

As to transmission, do you really need to send the raw data to the phone? If you're planning to graph it, perhaps you do, but if not, the Arduino can take care of collecting max min and average for you and then you can be much less concerned with the time taken to transmit it.
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 « Reply #5 on: December 05, 2011, 08:37:49 am » Bigger Smaller Reset

If you want to use a potential divider to halve the output voltage you need to check the output impedance of the sensor...
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"In this house, we obey the Laws of Thermodynamics" Homer J. Simpson
 « Reply #6 on: December 05, 2011, 02:53:29 pm » Bigger Smaller Reset

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As to transmission, do you really need to send the raw data to the phone? If you're planning to graph it, perhaps you do
It would make more sense to get the data onto a PC with a decent screen, spreadsheet and printer. Why use a phone as the interface for an industrial measurement machine, it seems like pain for no gain.
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 « Reply #7 on: December 05, 2011, 04:28:41 pm » Bigger Smaller Reset

@AWOL: So the packages are max 8bits. How big can the data(number) be inside this package?
Is this 28=256 bits so I have an accuracy of 2mm/256=0,0078mm? Or do I also need some start and stop bits, if this is the case how much bits are those start and stop bits per package?

@zoomket: Just discovered the third pin on a potentiometer . This is an easy solution indeed, thanks for the tip.

@Radman: I was also also thinking about sending the data to a laptop because they most probably are going to use the data on a pc. The Smart phone would just be handy to see a quick result. It’s a small and handy interface; also if I can show this to my teachers, they will be stunned I think. We do need the bluetoothconnection because the place where the sensor is mounted is really hard to reach at some places.

@wildbill: the range of my sensor is from 0,5mm to 2mm with an accuracy of 10µm. The accuracy of our whole measurementmachine needs to be minimum 0,05mm. Thanks for giving me the advice of the max and min. Where can I find a good manual for the programming? I already learned to program in Java so I almost understand everything about the commands.

@MarkT: The impedance of the sensor would be 5000 ohm. Is this good? And why do I need to check this?

Thanks again for the help and the tips
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"In this house, we obey the Laws of Thermodynamics" Homer J. Simpson
 « Reply #8 on: December 07, 2011, 02:42:43 pm » Bigger Smaller Reset

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We do need the bluetoothconnection because the place where the sensor is mounted is really hard to reach at some places.
I don't have a good image of the machine in my head. I can see the sensor might be in awkward locations but would the arduino, and could the laptop not also give a quick view? Your teachers might find the bluetooth novel but, if they are working to a marking plan, do they have any marks to award for it and will your effort be proportional to what you might gain? I am just suggesting a bit of caution because I have seen people get carried away with bells and whistles on the periphery of projects and fail to achieve their core objectives. Mobiles are being used more for monitoring equipment but usually for a specific objective e.g. equipment at lots of different geographic locations notifying an operator of important events as he moves about.
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 « Reply #9 on: December 08, 2011, 01:19:26 pm » Bigger Smaller Reset

I'm new with all the arduino-stuff but is it that hard to make a bluetoothconnection? Our main objective is the link between the arduino who sends the data to a laptop. We could also use a really long usb-cable but I taught making the bluetoothconnection wasn't so hard.
We will only start experimenting with the android phone when our objective is already reached. I also looked some information up about amarino and it seems that a lot of people are using it. That doesn't make it easy  but when we have enough time, I taught it might work. Making the app does seem hard to me.

Greetz
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"In this house, we obey the Laws of Thermodynamics" Homer J. Simpson
 « Reply #10 on: December 09, 2011, 05:45:16 pm » Bigger Smaller Reset

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We will only start experimenting with the android phone when our objective is already reached.
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So in my project I have to measure the distance between a turbine blade and the housing of the turbine when the turbine is spinning with a low speed.

About 50% of your original post concerned bluetooth, though you started by saying you had to "design a measurement device as a Masterproject".

If I was judging a competition for a measurement device I would be looking for;
• accuracy
• reproducibility
• robustness
• ease of use
• cost

The core objective does not mention interfaces at all. The only thing you have to do is measure a distance accurately - of course that could mean a lot of things. I would check with your teacher/tutor what the marking scheme is that should be public information. The real problem is probably in making the measurement, what is "slow speed", is there a lot of vibration, what are the tolerances on the turbine blades, what are the environmental conditions etc. could blade coatings affect your sensor.

Since you are talking about really long usb cables you are also probable missing out some important details e.g. where is the sensor in relation to the Arduino, and the Arduini in relation to the PC.

Most projects have limited time, all I am saying is spend you time wisely.
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