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accelerometer

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Cyborg

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Yeah I wanna make something that can send values for example when acar is moving i want it to send values as long as it is moving. Also I want the values when the car is going maybe 30mph to be different with when its going at 40mph or 10mph.In other words a digital motion detecor conected to a pic which will send the values. It kind of hard to explain but I was thinking of using an accelerometer so does anybody have any suggestions.
Thanks in advance
 
Cyborg said:
Yeah I wanna make something that can send values for example when acar is moving i want it to send values as long as it is moving. Also I want the values when the car is going maybe 30mph to be different with when its going at 40mph or 10mph.In other words a digital motion detecor conected to a pic which will send the values. It kind of hard to explain but I was thinking of using an accelerometer so does anybody have any suggestions.
Thanks in advance

An accelerometer only detects acceleration - a change in speed! - so at a fixed speed will give no output.

Your car already has a speed sensor, take an output from that!.
 
Integrate?

If you are attempting integrate over time to get the speed, I'd be very intersted in knowing the accuracy of the results. If it does work, maybe you can resolve position?
 
re

I guess I'll just use an accelerometer in a different way cause I wanted something digital and small in size. I'm thinking of making it to measure acceleration and deacceleration so if it accelerated and not deaccelerated yet, that means it is in motion and if deaccelerates then that means its stoping.So accelerometer wil be fine.
Thanks anyway :wink:
 
according to a professor of mine, a couple years ago someone built a senior project that used a 2-axis accelerometer and integrated to keep track of velocity and direction, and from that, build a map of where you went. he attached it to a bicycle, and left the engineering building and pedaled all over campus, and came back to where he started, and when he got back he plugged it into a computer and it showed his entire path, and shockingly enough it actually ended exactly where he had begun. I was pretty amazed at that, he must have used some pretty high-precision math.

if you used it in a car, it would be very interesting to see how close it could stay. like, drive for 10 minutes at various speeds and then come to a stop and see how close it reads to zero. perhaps with some sort of zeroing mechanism, so that, say, it zeros itself whenever your car is stopped, you could probably get decent accuracy.
 
re

Hey Thats Exactly what i'm making except i'll use it in a car not bicycle.I'll try my best, I know it takes alot of math (I'm a highschool junior)
 
A 2 axis is not accurate enough for that. Especially on a bike, unless it's a 3 wheeler and has no lean to it. Once the vehicle leans, gravity effects the reading, or force is tranfered to that 3rd axis, which is unread. I have an ADXL202 on a prototype datalogger for my racecar, and I'm working on moving to 3 axis to compensate for lean.
 
I don't buy the professor story. You can get some results of absolute speed with an accelerometer if you calibrate it and either keep it at a constant temp or calibrate for all temps, but the accuracy is still limited. More to the point, you must be able to keep track of what direction the accelerometer is pointed. There are great high-precision directional gyros out there for aircraft but the solid state, practical, affordable ones do not give absolute direction with great accuracy.

You won't see as much error since you're not trying to get position like the professor, and you can keep the device in the direction of travel, although suspension roll will mess with it a little bit. Long term accuracy just isn't practical.
 
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