Wanted - rPi Testing Device for Research Project


19 posts
by atgrace » Sun Dec 09, 2012 9:24 pm
Hi All,
I have a research project that I'm hoping a Raspberry Pi device could simplify.

The device would need to have an accelerometer, a display (nothing special, black and white, 16x2), and probably 4 buttons.

I've never used a Raspberry Pi and I don't have experience with any of the typical programming languages. For those reasons, I'm hoping to get bids to have the device developed and the application written. I know the Raspberry Pi movement is all about DIY but I imagine it'd take me too long to figure this out by myself.

To sum up the project, I'd like to use the Raspberry Pi to detect the angle (along only one axis) and visually represent a setting above, below, or identical to the current setting (referred to as a reference point.) This will be used to show the user of another device what setting they should use. So, when the Raspberry Pi is level, it should suggest a neutral setting. As the Raspberry Pi is tilted clockwise along the axis being monitored, it would progressively suggest setting changes associated with the particular angle change. The user would monitor the setting they were using by pressing the buttons to change the reference point (being the current setting) on the screen. Then, as the angle of the device decreases, it'd work backwards, informing the user to turn the setting down.

I see the graphical part of the system being accomplished with asterisks. A solid asterisk would show the setting that the user is currently using (the reference point) while a flashing asterisk would show the suggested setting. There would be a total of 7 settings below neutral (taking screen characters 1-7), a neutral setting (taking screen character 8), and 7 settings above neutral (taking screen characters 9-15.)

The neutral character would display a dash (-) when unoccupied by a setting or suggested setting. When it was the suggested setting, it'd display the flashing asterisk. When it was the current setting, it'd display a solid asterisk.

So, you'd have a button that'd move the reference point to the right, a button to move the reference point to the left, a button that would "zero out" the system (change the reference point to the neutral setting regardless of where it was previously), and a calibration button that would set the current device angle as the neutral angle. The left, right, and "zero out" buttons would need to be on a wire that could be positioned 4-5 feet from the Raspberry Pi. The Raspberry Pi, accelerometer, and the calibration button could all be together. The screen should probably be connected via wires, too, so that it can be positioned as necessary for viewing.

I would like the device to allow me to define the settings (perhaps via a .TXT file?) The settings file should allow me to enter the angles above or below the neutral point at which the suggested setting will change. That means there will be a total of 14 settings that will be define (7 above and 7 below the neutral point.)

The device needs to be fairly accurate since the 7 settings above and below will typically be within just a few degrees of each other.

It'd be nice (but not required) if the device could log each time the suggested setting updated, the reference setting changed, and the time at which the changes occurred. This could be output via whatever file method is easiest (a CSV, perhaps?)

This may be very complex or very simple; I have no reference point by which to gauge. In any case, this is a research project that is self-funded so I'd obviously love to complete it as cheaply as possible.

The person who accepts the project would need to buy the rPi and all supplies and then ship the completed device to me. Please include the cost of the supplies and the shipping costs when calculating your bid. I'd also appreciate a time frame in which you could complete the project.

I look forward to receiving your feedback, questions, and bids.
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by liz » Sun Dec 09, 2012 9:30 pm
Good grief: I'm looking forward to the feedback too. :roll:
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by atgrace » Sun Dec 09, 2012 9:36 pm
liz wrote:Good grief: I'm looking forward to the feedback too. :roll:


Sorry Liz, did I do something wrong or is it just a confusing mess?
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by poing » Sun Dec 09, 2012 9:40 pm
It's a confusing mess :?
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by atgrace » Sun Dec 09, 2012 9:42 pm
poing wrote:It's a confusing mess :?


Sorry, it is very hard (at least in my experience) to represent system requirements solely with text. It doesn't help that I can't divulge the full details of my research project.

Any way that you feel I could clarify?
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by ghans » Sun Dec 09, 2012 9:46 pm
Pictures. We love pictures ! (but please scale them down properly)


ghans
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by atgrace » Mon Dec 10, 2012 12:07 am
Does this help clarify?
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by pygmy_giant » Mon Dec 10, 2012 12:11 am
I think you effectively wan't some kind of digital spirit level?

I would recommend the Ivansense 6050 : http://www.raspberrypi.org/phpBB3/viewtopic.php?f=37&t=22266&p=210504#p210504 or just a mercury tilt switch if you only need to know whether the Pi is level, not how unlevel it is.
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by poing » Mon Dec 10, 2012 7:33 am
I'd get a cheap Android phone (something like this: http://www.boostmobile.com/shop/phones/samsung-galaxy-prevail/) with an accelerometer inside and contract an Android developer.
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by BertM » Mon Dec 10, 2012 12:50 pm
A Raspberry Pi is definitely overkill for this application, although it can of course be used to accomplish the same goal.

For a such a device I would suggest using a simple ATmega microcontroller - like the Arduino - combined with a serial output accelerometer (such as the MMA8452Q). Such microcontrollers are more than powerful enough, and consume nearly no power (unlike the Raspberry Pi) making a battery powered device possible.
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by rurwin » Mon Dec 10, 2012 1:55 pm
I can see three difficulties with this spec.

1. The suggested accuracy is going to be close to the resolution of the device. The difference between 1 degree and 2 degrees is less than one LSB of a 12-bit accelerometer. It's about half a milli-g. Add noise and vibration into the equation, and it is not certain that the accuracy you need can be obtained with cheap components.

2. Building the entire device is going to limit you and be expensive. It would be far better to specify a 3-axis accelerometer in a box with an RS232 serial connection. Then just connect that up to a laptop -- or a RaspPi -- with all the buttons on a GUI.

3. By specifying an accelerometer you are blocking several possible solutions that might be cheaper and more effective. For example, two linear potentiometers in a bridge arrangement with adjustable zero and gain might give you what you want for less than the cost of a RaspPi. An adjustable protractor and a plumb-line is even cheaper. If that isn't accurate enough, then make the pendulum solid and connect it with some gears to a dial.
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by joan » Mon Dec 10, 2012 2:33 pm
rurwin wrote:I can see three difficulties with this spec.

1. The suggested accuracy is going to be close to the resolution of the device. The difference between 1 degree and 2 degrees is less than one LSB of a 12-bit accelerometer. It's about half a milli-g. Add noise and vibration into the equation, and it is not certain that the accuracy you need can be obtained with cheap components.

...

I think one of the cheap IMUs would meet the requirements , one with 9 axis degrees of freedom such as ITG3200/ITG3205 + ADXL345 + HMC5883L.

The combination of gyro and accelerometer should work.
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by joan » Mon Dec 10, 2012 2:39 pm
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by paultnl » Mon Dec 10, 2012 2:49 pm
I don't like Russian dolls, they are so full of themselves
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by Doowybbob » Mon Dec 10, 2012 4:05 pm
An arduino would fit this project much better, much more cost effective and efficient.

However, OP states they would like a configurable settings file, this means the arduino will need some connection to external memory if I'm not mistaken. The options for that would be either connecting it through serial to a computer (possibly a Rpi) or attaching an sd-card that hold the config file.
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by atgrace » Mon Dec 10, 2012 4:17 pm
I appreciate the feedback and assistance from everyone....especially considering my request is so lengthy and unclear.

I'm going to give the Android suggestion some further though and investigation. I think this might be a great solution since, long term, this could be easily replicated should I decide to scale up my research to include more participants.

Thanks again!
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by joan » Mon Dec 10, 2012 4:25 pm
Several Arduinos have flash memory which can be used for configuration data. E.g. the Nano.

Someone did a head tracker video on Youtube usng a 9 DOF IMU and a Nano. Plenty of similar videos. I can't find the one I was thinking of at the moment. It would be useful to the OP as it had links to the software source code.
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by marked » Mon Dec 10, 2012 8:37 pm
Something like this?

https://play.google.com/store/apps/deta ... protractor

They also do a bundle with other tools that generally turns up in a Play Store sale.

mark
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by atgrace » Tue Dec 11, 2012 4:56 am
marked wrote:Something like this?

https://play.google.com/store/apps/deta ... protractor

They also do a bundle with other tools that generally turns up in a Play Store sale.

mark


That looks helpful. I also found an iPad/iPhone app called SensorLog that can track and report all of this data. I'm going to do some testing with exports from that and then decide how to proceed.

I truly appreciate the guidance and suggestions!
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