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Logging Bluetooth Accelerometer Data on a PDA?
sessha asks: "I want to log data from a Bluetooth Accelerometer (actually 5) attached to different parts of the body. How one would go about logging the data onto a bluetooth compatible PDA. I know quite little about PDA OS's, but the main concern is functionality - it doesn't matter if it is PalmOS or Windows CE or whatever. The Linux and Windows directions for data logging are shown, but how would one best go about this on a PDA? Also, it would require at least 256 MB storage, preferably more, since this will be recording 300 of these ASCII strings a second for a number of days. Suggestions as to the best equipment and software to use for such an endeavor would be greatly appreciated."
lets see, 16 bytes / string at 300hz gives us
16*300*60*60*24 = 414720000 bytes/day or about 400megs / day
If instead you use a simple binary representation with 6bytes/record we get
6*300*60*60*24 = 155520000 byets/day or about 150megs / day
I bet the data would compress really well, but if a pda would have enough horspower to log and compress is an open question, I would guess yes.
ps
If you want to play with bits and save 2 more bits per record then we get:
5.75*300*60*60*24 = 149040000 bytes/day
Thoughts on tech, Software Engineering, and stuff
The other issue you'll want to look into is battery life. I was talking just today with someone from PalmOne about their models with an eye to finding something with a long enough battery life to be used for a week without charging in a 25% utilization scenario. They don't have such a beast. They spec them for about 10 hours of normal use, but heavy data logging isn't normal use - it's high memory bandwidth and that will cost you power. On the flip side, you don't actually need the screen running, so if you can turn that off it will help.
Given that WinCE based devices are generally known for shorter battery lives, I'm not so sure that your request is practical with current technology.
Now, what about an Ipod-style device? They have big hard disks, and they're designed to run for many hours. That's where I'd be looking - either that or those new-fangled 'wearable computer' things that have a hard disk and a bluetooth adaptor and can be thrown in your bag to allow you to access your personal storage at any computer.
Is indeterminate write times. You're most likely working with flash memory. Flash memory write completion times will vary depending on the device, the block size, and the wear-leveling algorithm used. You probably won't have much control over anything other than block size. You'll have to think about when to close and open the file as well. Frequent file commits will improve recovery from errors, but will also probably increase write times.
This is really a job for an embedded computer engineer. If there's money, safety or reputation at stake, I urge you to find one to help you.
"Eve of Destruction", it's not just for old hippies anymore...
Simputer has a built-in Accelerometer and it runs Linux. Since this device already has built-in support for accelerometer, it should be relatively easy to add support for more using the SDK. Also, simputer can use USB flash memory. It also is one of the rare pda-size devices that has 2 USB ports (one master and one slave; most PDA's only have a slave USB where you can not plug any other usb device). It also has IR port. I am not sure how bluetooth would fit in but it shouldn't be too difficult with a device with such features...