Building a vibration sensor

[mmilbury]

I'm building an acceleration sensor for a project with low g's. (.05<g<1.0 max g = 2.0) I've researched several sensors on the web and have selected a sensor with a sensitivity of 120 pV/g.

My understanding is there is a known mass that reacts to the vibration. This reaction is output as a certain voltage. What I am attempting to do is interface my accelerometer with a circuit board.

Would anybody know how I would do this? I would like to make a direct connection to the ADC without using an amplifier circuit. With this in mind, what would be the best way to do this? If I go as high as 2.0g's would you know how I could limit this voltage to keep it from overloading the processor?

Any help would be greatly appreciated.

 

[buzzp]

If you don't want to amplify the signal then I think your asking for trouble with pico volt signals. Noise is often much larger than this in magnitude. Are you planning on using a filter? Also, 240 pV will not hurt your processor at all. You might consider putting a zener diode in on the input to the processor to protect it if you end up with a direct connection.

 

[Chancy99]

Which sensor are you using ? Reason I ask is that there are several interface methods available from these types of devices.

For example, I'm familiar with the ADXL202 G-sensors

http://products.analog.com/products/info.asp?product=ADXL202

Also, here's a nice little project for an automotive G sensor using the ADXL202.

http://www.ghg.net/stuart/accelerometer/accelerometer.html

The ADXL202 can interface to the microcontroller in two ways. One is using a pulse-width-modulated signal, where the G force is represented by the ratio of the pulse duty cycle to the pulse width. No voltage levels to worry about. If you want to talk directly to an A/D, then you can pull the actual analog signal from before the filter caps and measure it yourself.

Search google for adxl202 - there are lots of hits.

Dean.

 

[buzz41]

I am suspicious of the picovolt ref. That is a tiny 240*10^-12 volt, way down in thermal noise and too low for common interfacing.

channey99 - Hi. Good refs on the devices.
A little OT for the thread, but I stumbled onto a link with some Toyota interface details. It might be useful to you for your datalogger proj, in case you don't have it. This is the top page:

http://www.autoshop101.com/autoshop28.html

ron