question with accelerometers

[atbrown]

I'm fairly new to robotics yet have made a few small spin-offs of the $50 robot.  I have a basic question about accelerometers.  My goal is to place a sensor on an obstacle and when the obstacle is moved the sensor will turn on a pre-recorded message similar to those greeting cards that play a tune when opened.  If you must know, I want to place it in my shoes, so when the dog tries to run off with my damn shoes again, it'll get yelled at...stupid?...I know!!  Obviously this is just something I'm doing for fun while bored, so I want this to be very affordable and I'm hoping the cheapest accelerometer will work.  What type and specs should I look for in the particular accelerometer and does anyone have a simple schematic that acts similar that I may be able to use (ie. turns on an LED, etc.)?

Thank you.

[z.s.tar.gz]

You're more than likely going to need a microcontroller to read the accelerometer, but for an even cheaper solution, you could do like they do in light-up pens and stuff like that:
Put a little spring inside a little metal cylinder to where they're almost touching. That way when you move it around, the spring touches the cylinder completing the circuit.
Since you don't actually need a numerical value for acceleration, that would be a far cheaper option.

[madsci1016]

If you are dead set on using a accelerometer, you can use an "Op-Amp Comparator" to trigger a device when the accelerometer is moved.



Read about it here: (scroll down a bit)

http://www.swarthmore.edu/NatSci/echeeve1/Class/e72/E72L2/Lab2%28OpAmp%29.html

Accel's output an analog voltage based on accel due to gravity. So you would set the comparator to trigger to what voltage (and there by force/orientation ) to trigger at.

[madsci1016]

And you could use this to play a message:

http://www.radioshack.com/product/index.jsp?productId=2102855

and a sensor like this is fine

http://www.sparkfun.com/commerce/product_info.php?products_id=252

So total project cost would be around 30-40 bucks.

[HyperNerd]

I saw a message greeting card thing once which let you record your own message, and you could do it multiple times.

If you were to gut one of these cards then modify it a bit, it could be a very cheap way (with the spring in a cylinder thing) to make your device.

 -HyperNerd

[Soeren]

Hi,

If you must know, I want to place it in my shoes, so when the dog tries to run off with my damn shoes again, it'll get yelled at.

No need for an accelerometer to do that. A simple trembler switch will do.