SparkFun Forums

[Napthali]

I'm hoping to use one of the Sense-SerAccel-v5-D units in a project I'm working on to record the forces a rider experiences on a roller coaster. I have a few questions, though, and was hoping that some folks here might have an idea or two.

First off: I'm planning on using a Sharp Zaurus 5500 to record the data. Unfortunately, the Zaurus doesn't supply enough power over its serial connection to activate the accelerometer. If I power the accelerometer from an external source (say, with the VCC and GND solder points on the board), will I still be able to use the serial port to gather data?

Secondly: I've been told that filtering the data is going to be crucial to getting a good signal, and that something like Matlab is necessary to really get usable information. Is that true from a hobbyist perspective? The person telling me this typically uses accelerometers to measure forces in scientific car crash studies, so perhaps his standards are higher than mine.


(FYI: The project page is http://coaster-metrics.blogspot.com/, if you're curious.)

[Philba]

you will need filtering but matlab isn't the only way to do it. If you can store the raw samples on the zaurus, you could process it on a a pc. there are tons of pages out there on filtering. matlab will make it easier to play with the data and try different filters. I think people tend to forget that matlab is just a program.

no problem with providing seperate power, just make sure you have common grounds. I'd look to making the most compact, sturdy package possible.

[Napthali]

I'm sorry, I'm a tad ignorant on electrical matters. Could you elaborate on what you mean by "common grounds"?

Thanks for the advice on filtering. I was planning on just recording the raw hex values onto the Zaurus anyways, so it seems I'll have plenty of options for massaging the data off-line.

[Philba]

when you power parts of a circuit from different supplies, the grounds must be hooked together - "common". In your case, the ground of the zaurus (on the serial connection) needs to be connected to the ground of the accelerometer. if you use a standard rs232 connection (which has ground) it should just work but lots of people neglect that point.

[Napthali]

But I would only have one power source for the circuit... the solder points, yes? Or are you saying I should take whatever power the Zaurus provides and make up the difference with the on-board connectors?

I guess what I'm asking is... is it possible to power the circuit on the board but still use the serial connector just for data purposes, ignoring the power pins altogether? Or does power have to run through the serial connector in order to get the data off of there?

Sorry if I seem a little obtuse... I'm usually a software guy.