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1  Using Arduino / General Electronics / Re: Question about the analog input of "Arduino mega 2560 " on: February 09, 2013, 09:16:23 pm
May this post enabling differential input for Arduino handy.. http://arduino.cc/forum/index.php/topic,147830.msg1110852.html#msg1110852
2  Using Arduino / Sensors / Re: Mini Aref on: February 09, 2013, 08:55:47 pm
Do you ever try to use external power supply? USB power only supply your system under 500 mA.
3  Using Arduino / Sensors / Re: Differential Connections analog input on: February 09, 2013, 08:47:02 pm
Set your ADC V reference with external high precision reference. While you need external ADC, use LTC2473 16-bit differential ADC. Common problem on low voltage measurement is weak signal to noise ratio.
4  Topics / Science and Measurement / Re: MMA7361 accelerometer frequency response? on: February 09, 2013, 08:10:52 pm
Did you not see in the datsheet (http://www.sparkfun.com/datasheets/Components/General/MMA7361L.pdf) where is says:

Bandwidth Response
XY  Typically 400 Hz
Z    Typically 300 Hz


Since the sensitivity and zero offset will vary with temperature you might want to have your accelerometer in a temperature-controlled environment.  The operating temperature range goes up to 85°C so a little oven to keep the temperature around 40°C might do the trick.

OK, thanks for advice. I will do temperature test first.
5  Topics / Science and Measurement / MMA7361 accelerometer frequency response? on: February 09, 2013, 02:09:24 am
I want to create a simple seismometer based on MMA7361 accelerometer. I read from many literature about seismic wave frequency and peak ground acceleration (PGA). It is clear that MMA7361 qualified for acceleration measuring range 1.5 g or 6 g (maximum earthquake acceleration recorded in history is about 1,24 g). But, it is not defined (on datasheet) about frequency response of this sensor. Seismic wave frequency range (non exploration) can be smaller than 0.001 Hz and maximum frequency up to 200 Hz.

Is this MMA7361 frequency response qualified for frequency from 0.001 Hz to 200 Hz? Anybody testing frequency response this MMA7361 accelerometer?
6  Using Arduino / General Electronics / Re: Resistors, Voltage vs Current on: February 09, 2013, 01:21:53 am
May I ask about the metering device (multimeter) that you use? Almost multimeter had error reading (usually described on user manual). It also have input impedance, usually analog voltmeter have 20kohm input impedance. With your 10k resistor its about 50% of input impedance. Almost digital voltmeter comes with 100kohm or greater. Theoretically, greater input impedance voltmeter give you better measurement. Assume you use digital voltmeter with 1Mohm, its about 1% but still affect your result.
Other analysis, may your resistor relative value about 5% (with gold color sign), More precision and accurate resistor will give you better result. Use resistor with 1% relative value or smaller.
7  Using Arduino / Sensors / Differential Sensing with Arduino on: February 08, 2013, 11:56:29 pm
I've been making enable differential input (and also gain enable) on Arduino ADC by add wiring_differential.c into arduino library. I try to recording sinewave with 2 V amplitude (generate from signal generator) without DC offset. It looks like this while i graph it on spreadshet,

Download library and sample from here: http://sekarlangit.com/wp-content/uploads/2013/02/AnalogDiff.tar.gz. Else, download from attachment.

I wrote complete post about this differential input but may it goes wrong for the table (please correct me). Here: http://sekarlangit.com/arduino-differential-gain.php

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