An interesting way to increase sensitivity and reduce the noise of the ADXL335 analog accelerometer.

The ADXL335 is a low power, complete 3-axis accelerometer with analog voltage outputs. The product measures acceleration with a minimum full-scale range of ±3 g.It can measure the static acceleration of gravity in tilt-sensing applications, as well as dynamic acceleration resulting from motion, shock, or vibration. Sensitivity is 330 mV/G.

Besides many “earthquake detector” projects on the Internet that use this accelerometer, its sensitivity for this purpose is very low so these devices are practically non-functional. I am confident in this because I have made and tested many of them.

The idea presented below is: with the help of instrumental operational amplifier IC connected in DIFFERENTIAL mode to amplify only the USEFUL part of the signal by 100-1000 times (or more) without amplifying the harmful noise. I use OP07 IC, but any instrumental operational amplifier IC can be used. Using the potentiometer P1 we set the voltage V2 to be slightly less than V1, and P2 adjusts the amplification of useful signal. The formula for the coefficient of amplification is Vout=(V1-V2)*K where K=1+100/P2(kOhm). This amplified signal connects to an analogue input of an Arduino microcontroller through a 1k resistor. To amplify the three outputs of the ADXL335 we need to make three such identical amplifiers for each axle (x, y and z) separately. In this case I only use one axis (z) to detect vertical shocks.”


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