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1  Using Arduino / Sensors / Re: Measuring real-time displacement of large steel cable in motion on: Today at 12:43:06 pm
You've certainly piqued my interest! I assume you are talking about restraints within the code or data, as I can't restrain the physical motion of the cable in any way.

What kinds of restraints are you thinking of? Are there any standard terms that I can research to learn how to approach this problem?
2  Using Arduino / Sensors / Re: Measuring real-time displacement of large steel cable in motion on: September 22, 2014, 06:09:03 pm
As I said above, it looked to be about a couple of inches of movement in each direction.
3  Using Arduino / Sensors / Re: Measuring real-time displacement of large steel cable in motion on: September 22, 2014, 01:59:45 pm
In my experience, simply taking the double integral of accelerometer data results in a huge amount of error that makes any position data pretty much useless.

What I'm looking for is a way to use an accelerometer (or any other sensor you can recommend) to measure the amount and direction of movement of a large vibrating cable in multiple dimensions.

If an accelerometer is not practical for this, I completely understand. Can anyone think of any clever alternatives for measuring the data I'm looking for?
4  Using Arduino / Sensors / Re: Measuring real-time displacement of large steel cable in motion on: September 21, 2014, 09:21:42 pm
And that's what I'm most interested in finding out - how to approximate the displacement (as accurately as possible).

I understand that the standard math answer to take the double integral of the acceleration, but this generally has too much drift to be used for more than a few seconds at a time.

What kinds of existing implementations can I make use of to approximate the position / displacement based on accelerometer data in real-time? Are there any useful libraries or code examples that I can make use of that do it 'the right way', rather than having to try to do it (crudely) myself?
5  Using Arduino / Sensors / Re: Measuring real-time displacement of large steel cable in motion on: September 21, 2014, 06:33:16 pm
We are talking about steel cables on a suspension bridge, so we're talking about a good couple inches of motion in any direction, depending on how hard the wind is blowing. I would expect frequency to be in the range of 5-10 Hz or so, but this is the kind of information that I am aiming to find out through measuring it accurately.
6  Using Arduino / Sensors / Measuring real-time displacement of large steel cable in motion on: September 21, 2014, 04:09:11 pm
I'm working on a project where I must find a way to measure the displacement of a large steel cable as it vibrates (imagine a cable on a suspension bridge). I'd really like to be able to measure as much information as accurately as possible to learn about the various kinds of motions that are going on, but I'd like to get some advice about types of sensors to go for.

Ideally I would like to be able to measure the relative displacement of the cable in real-time, to both measure the frequency of vibration and the amplitude in various directions (it might be swaying up-down more than left-right, for example).

I'm considering grabbing a 9-DOF IMU breakout from Adafruit (http://www.adafruit.com/products/1714) but I'm a little bit stumped on how to actually obtain the information I'm interested in out of the raw data streams.

Do there exist any libraries, code examples or prior open-source work that I can look to to get some insight about how to wrangle this data (ideally in real-time)?

If there is another sensor or approach that you would recommend, I'm all ears! Just keep in mind that I need something that can be physically attached to the large cable and easily moved around so I can run multiple experiments.
7  Using Arduino / Sensors / Re: Strange oscillation on electret mic circuit clone on: February 18, 2014, 11:54:35 am
Interesting. I turned the electret around and am getting a nearly identical graph. If it was truly a polar device I would expect it behave very differently.  Attached is an image of what the new graph looks like.

While the oscillation is still there, it does seem like the signal is less noisy. I am beginning to think that the RC circuit on the artificial ground of the op-amp is causing the oscillation, but not sure what to do about it.

Edit:: Thought it might be helpful to list the mic and op-amp I sourced for my design, perhaps I overlooked something in the specs that could be causing this.

Elecret mic: http://www.digikey.com/product-search/en?x=0&y=0&lang=en&site=us&KeyWords=102-1721-ND
Op-amp (OPA344): http://www.digikey.com/product-detail/en/OPA344NA%2F250/OPA344NATR-ND/362264
8  Using Arduino / Sensors / Re: Strange oscillation on electret mic circuit clone on: February 15, 2014, 10:07:00 pm
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Have you checked the values of the resistors you fitted around the IC, it looks like you have way too much gain and that is causing  the oscillations.

Two of the 10ks actually measure as being around 5.76k, but I get the exact same result on the Sparkfun breakout board.

I find it hard to believe that the gain is too high. As I said, this is the exact schematic from the Sparkfun breakout board, which I've tested and found to work perfectly.

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I see that you have added extra circuits to your board, have  you tried the board with just the microphone circuit

Haven't tried that, will need to order all new parts to try that.

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is the microphone in the correct way

I had no idea that elecrets had polarity - are you sure about that? The mic can only be connected in one way for the silkscreen to match the actual part, so I had been going off that.

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add a cap, 1 to 10uF across the supply at the amp chip, along with a 0.1uF cap

I will if the problem can't be resolved in some other way. I'm getting really tired of the time and money it takes to produce PCBs and assemble prototypes.
9  Using Arduino / Sensors / Re: Strange oscillation on electret mic circuit clone on: February 15, 2014, 07:50:09 pm
On second thought, adding the 10pF capacitor in parallel may not have caused a DC offset - it may have lessened the peaks and troughs of the oscillation. Can you confirm that as what I'm seeing? If so, maybe I need to order a replacement cap.
10  Using Arduino / Sensors / Re: Strange oscillation on electret mic circuit clone on: February 15, 2014, 07:46:24 pm
Adding a 10pF cap in parallel to the 12pf one seems to make it a little worse. The voltage shifts upward, but the oscillation is unchanged. Attached is a pic of a graph with it in place.

I've also attached a picture of the board design for the Sparkfun breakout board. I modified the layout slightly to fit my board, but don't understand what could be so different to break the functionality.

I've also attached the Eagle files for the Sparkfun breakout board so you can check more thoroughly.
11  Using Arduino / Sensors / Re: Strange oscillation on electret mic circuit clone on: February 15, 2014, 10:32:54 am
There are ground planes on the top and bottom of the board.

Attached the schematic. I want to stress that this is an exact copy of Sparkfun's electret mic board, which I have tested alongside my own sensor module and found to work perfectly. I am very confident that the problem is not with the schematic, but with the board design.
12  Using Arduino / Sensors / Re: angle sensor on: February 14, 2014, 04:34:19 pm
I believe this is often done using a quadrature encoder. Essentially a photosensor that doesn't move (on the frame of your bot) and a spinning wheel with alternating black and white swatches on it. The voltage of the photosensr will indicate whether it is looking at black or white, and you can keep track of that information in the code to extrapolate position.
13  Using Arduino / Sensors / Re: Arduino and a video camera on: February 14, 2014, 04:31:49 pm
The Arduino is not capable of computer vision problems like this - they are just too computationally intense. Try the RasPi or Beaglebone - the RasPi has several camera modules that connect directly to it.
14  Using Arduino / Sensors / Strange oscillation on electret mic circuit clone on: February 14, 2014, 04:30:49 pm
I bought an electret mic breakout board (https://www.sparkfun.com/products/9964) and was able to get it to work quite well, so I decided to use the circuit in an open-source sensor module that I am working on. I received the PCBs from OSHPark yesterday and assembled the first prototype, but am getting some strange readings.

Without doing any sort of buffering or averaging, I'm just outputting the direct results of an analogRead to the serial port and monitoring it in the Arduino IDE. Without making any noise, I'm seeing a very regular oscillation occurring in the signal that is making it impossible to use. When I tap the electret I am able to make the signal top out, but the oscillating noise is still there.

I put together a Processing sketch that just graphs the analog data being received straight from my Arduino. I've attached a screenshot of the sketch running (purple graph on black background image).

've never designed an audio circuit before, so I'm not sure what is happening. I don't own an oscilloscope, nor do I know how to use one to troubleshoot a problem like this. Does anyone have some ideas about what is going on, and what I can do to solve the oscillation?

I've attached the Eagle files (schematic and PCB file) for my board, as well as an image of the PCB if that helps.

I noticed that when I measure two of the 10k resistors with a multimeter I see ~5.76k instead of 10k. However, I see the same thing when I measure the same resistors on the Sparkfun BoB. Odd.

I also reviewed my BOM and found that I used some capacitors that had a tolerance of "-20%, +80%". I am wondering if the problems I am seeing are due these parts, or somehow general PCB design.

15  Using Arduino / Networking, Protocols, and Devices / Re: Microcontroller-based switching of AT mode for HC-05 Bluetooth module? on: November 18, 2013, 09:15:29 pm
I found out that I had the pin number wrong this whole time. I realized that the Bluetooth's TX pin was actually connected to PB4 (MISO) on the ATMega328, which is digital pin 12, not 8. I updated my code and can send and receive messages between terminals now via Bluetooth.

After getting the TX pin right, everything else was pretty trivial. Getting into AT mode is as simple as booting the board up and not pairing the module with anything. I am able to change the name and pin code of the module very easily, which is all I wanted to do. The command set for my module matches up with the commands listed in this (even though the photos show a strange looking module): http://www.mikrokopter.de/ucwiki/en/HC-06
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