Web Site: www.parallax.com Office: (916) 624-8333 Forums: forums.parallax.com Fax: (916) 624-8003 Sales: sales parallax.com Sales: (888) 512-1024 Technical: support parallax.com Tech Support: (888) 997-8267 Memsic 2125 Dual-Axis Accelerometer ( 28017) The Memsic 2125 is a low-cost thermal accelerometer capable of measuring tilt, collision, static and dynamic acceleration, rotation, and vibration with a range of 3 g on two axes. Memsic provides the 2125 IC in a surface-mount format. Parallax mounts the circuit on a tiny PCB providing all I/O connections so it can easily be inserted on a breadboard or through-hole prototype area. Features Measures 3 g on each axis Simple pulse output of g-force for each axis Convenient 6-pin 0.1 spacing DIP module Analog output of temperature (TOut pin) Fully temperature compensated over 0 to 70 C operating temperature range Key Specifications Application Ideas Power Requirements: 3.3 to 5 VDC Dual-axis tilt and acceleration sensing < 5 mA supply current for autonomous robot navigation Communication: TTL/CMOS R/C tilt controller or autopilot compatible 100 Hz PWM output signal Tilt-sensing Human Interface Device with duty cycle proportional to Motion/lack-of-motion sensor for acceleration alarm system Dimensions: 0.42 x 0.42 x 0.45 in Single-axis rotational angle and (10.7 x 10.7 x 11.8 mm) position sensing Operating temperature: 32 to 158 F (0 to 70 C) Theory of Operation The MX2125 has a chamber of gas with a heating element in the center and four temperature sensors around its edge. When the accelerometer is level, the hot gas pocket rises to the top-center of the chamber, and all the sensors will measure the same temperature. By tilting the accelerometer, the hot gas will collect closer to some of temperature sensors. By comparing the sensor temperatures, both static acceleration (gravity and tilt) and dynamic acceleration (like taking a ride in a car) can be detected. The MX2125 converts the temperature measurements into signals (pulse durations) that are easy for microcontrollers to measure and decipher. Copyright Parallax Inc. Memsic 2125 Dual-Axis Accelerometer ( 28017) v2.1 9/28/2012 Page 1 of 3 Pin Definitions For Memsic MXD2125GL pin ratings, see the manufacturers datasheet posted on the 28017 product page at www.parallax.com. Pin Name Function 1 Tout Temperature Out 2 Yout Y-axis PWM output 3 GND Ground -> 0 V 4 GND Ground -> 0 V 5 Xout X-axis PWM output 6 VDD Input voltage: +3.3 to +5 VDC Communication Protocol Each axis has a 100 Hz PWM duty cycle output in which acceleration is proportional to the ratio tHx/Tx. In practice, we have found that Tx is consistent so reliable results can be achieved by measuring only the duration of tHx. This is easy to accomplish with the BASIC Stamp PULSIN command or with the Propeller chips counter modules. With Vdd = 5V, 50% duty cycle corresponds to 0 g, but this will vary with each individual unit within a range of 48.7% to 51.3%. This zero offset may be different when using Vdd = 3.3 V. See the manufacturers datasheet for details. Example Circuit The example schematic and wiring diagram below are for the BASIC Stamp and Board of Education. The program below, SimpleTilt.bs2, simply measures the pulse width, that is, the duration of tHx, for each axis. The raw values are displayed in the BASIC Stamp Editors Debug Terminal. If you run the program, then tilt the accelerometer, you should see the values for each axis change. Copyright Parallax Inc. Memsic 2125 Dual-Axis Accelerometer ( 28017) v2.1 9/28/2012 Page 2 of 3