The accelerometer in this kit are very sensitive. Even a small touch changes the values very rapidly. I want to lower the sensitivity of the sensor. What is the way of doing this?
closed as not a real question by Olin Lathrop, Leon Heller, Brian Carlton, embedded.kyle, Dave Tweed♦ Apr 4 '13 at 23:19
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The accelerometer sensitivity can be set to +_/- 2g or +/- 8g - see below.
BUT what is the problem with the sensitivity being as it is?
Can you not just divide down the amplitude of the output to suit?
\ As long as the system does not "rail" under your tapping is it important that it has a large dynamic range?
Digikey has these for $US10.90 - an utter bargain.
L3GD20, ST MEMS motion sensor, 3-axis digital output gyroscope
LSM303DLHC, ST MEMS system-in-package featuring a 3D digital linear acceleration sensor and a 3D digital magnetic sensor
The user manual 36 page PDF says
4.7 E-compass/accelerometer MEMS (ST MEMS LSM303DLHC) The LSM303DLHC is an ultra-compact low-power system-in-package featuring a 3D digital linear acceleration sensor and a 3D digital magnetic sensor. It includes a sensing element and an IC interface able to provide the measured acceleration to the external world through I2C serial interface.
The LSM303DLHC has dynamically user-selectable full scales of ±2g/±8g and is capable of measuring acceleration, and a magnetic field full scale from ±1.3g to 8.1g with an output data rate of 100 Hz or 400 Hz. The STM32F303VCT6 MCU controls this motion sensor through the I2C interface.
• L3GD20, ST MEMS motion sensor, 3-axis digital output gyroscope
• LSM303DLHC, ST MEMS system-in-package featuring a
3D digital linear acceleration sensor and a
3D digital magnetic sensor
• Ten LEDs: – LD1 (red) for 3.3 V power on – LD2 (red/green) for USB communication – Eight user LEDS, LD3/10 (red), LD4/9 (blue), LD5/8 (orange) and LD6/7 (green)
• Two pushbuttons (user and reset)
• USB USER with Mini-B connector
• Extension header for all LQFP100 I/Os for quick connection to prototyping board and easy probing
Description The STM32F3DISCOVERY helps you to discover the STM32 F3 series Cortex-M4 mixed-signals features and to develop your applications easily. It includes everything required for beginners and experienced users to get started quickly. Based on the STM32F303VCT6, it includes an ST-LINK/V2 embedded debug tool, accelerometer, gyroscope and e-compass ST MEMS, USB connection, LEDs and pushbuttons. The STM32F3DISCOVERY discovery board does not support STM32F313xx MCUs (1.65 V to 1.95 V power supply). A large number of free ready-to-run application firmware examples are available on www.st.com/stm32f3discovery to support quick evaluation and development.
Depending on the specific behavior desired, two approaches suggest themselves:
- To retain the full available resolution of the sensor, yet reduce jittery output, one can average readings over time using a moving average: This is in effect like using a digital implementation of a low-pass filter, smoothing out the sharp variations, yet retaining the overall precision. How large a moving average set of data is used, will determine how rapidly the resultant averaged output will change with an actual change of acceleration on the sensor.
- For many purposes, the actual resolution required is way less than the sensor can generate. In such cases, the trivial solution is to simply reject the least significant n bits and use the rest: For instance, if only 10 bit data significance (9 bits, with positive or negative sign) is required, while the sensor provides 15 bits + sign, taking account of the sign and right-shifting the value by 6 bits will provide the required resolution, while eliminating the least significant 6 bits worth of jitter.
Besides the above, as other answers have pointed out, the sensitivity of the LSM303DLHC sensor provided in the kit can be reduced to ±2g, which should alleviate the issue somewhat.
The best (IMO) answer was also roundly down-voted because it was phrased as a suggestion. Here it is again as a statement:
If the accelerometer responds wildly when you touch it, don't touch it!
Acceleration = Force / Mass.
The mass of the accelerometer chip is very small. It only takes a tiny force to create a very large acceleration, if the force is applied to the chip only. When the chip is mounted, and the circuit board itself mounted into a device, for instance a Wii-remote, the mass that must be accelerated is much larger. The whole assembly is much less sensitive to disturbing forces.
That is not to say that signal conditioning, averaging and setting gain as described in previous answers, are not also part of what you need to do with the data from an accelerometer.