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Copyright © Parallax Inc. Memsic 2125 Dual-Axis Accelerometer (#28017) v2.1 9/28/2012 Page 1 of 3
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 prototyp e 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 temperat ure (TOut pin)
Fully temperature compensated over 0 to 70 °C
operating temperature range
Key Specifications
Power Requirements: 3.3 to 5 VDC;
< 5 mA supply current
Communication: TTL/CMOS
compatible 100 Hz PWM output signal
with duty cycle proportional to
acceleration
Dimensions: 0.42 x 0.42 x 0.45 in
(10.7 x 10.7 x 11.8 mm)
Operating temperature: 32 to 158 °F
(0 to 70 °C)
Application Ideas
Dual-axis tilt and acceleration sensing
for autonomous robot navigation
R/C tilt controller or autopilot
Tilt-sensing Human Interface Device
Motion/lack-of-motion sensor for
alarm system
Single-axis rotational angle and
position sensing
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 2 of 3
Pin Definitions
For Memsic MXD2125GL pin ratings, see the manufacturer’s 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 chip’s 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
manufacturer’s datasheet for details.
Example Circuit
The example schematic and wiring diagram below ar e 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 Editor’s 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 3 of 3
' Smart Sensors and Applications - SimpleTilt.bs2
' Measure room temperature tilt.
'{$STAMP BS2}
'{$PBASIC 2.5}
x VAR Word
y VAR Word
DEBUG CLS
DO
PULSIN 6, 1, x
PULSIN 7, 1, y
DEBUG HOME, DEC4 ? X, DEC4 ? Y
PAUSE 100
LOOP
Programming Resources and Downloads
BASIC Stamp
Stamps in Class Mini Projects — The BASIC Stamp example above is taken from the Stamps in
Class Mini Projects, which feature many topics specifically for the Dual-Axis Accelerometer. Some are
for the Board of Education or BASIC Stamp HomeWork Board alone; while others use a Boe-Bot
Robot or SumoBot. Look for the Stamps in Class Mini Projects sticky-thread in the Education forum
at forums.parallax.com. Also, look for more projects at learn.parallax.com.
The Memsic 2125 Demo Kit BASIC Stamp Source Code — this source code contains conditional
compile directives that allow it to be used with the BS2, BS2e, BS2sx, BS2p, and BS2pe. Look for this
on the 28017 product page at www.parallax.com.
Propeller Objects
Several Memsic 2125 Accelerometer code objects and applications
for the Propeller chip are available in the Propeller Object Exchange
(http://obex.parallax.com).
Below is a photograph of the high-speed Memsic MXD2125
Accelerometer Demo in action. This application “provides a high
speed assembly driver, and separate-cog and same-cog Spin
versions of the MXD2125 Dual Axis Accelerometer. The high speed
version displays the data on a television as a 3D wireframe plane
with normal vector.
Other Microcontrollers
Check for links to Memsic 2-axis Accelerometer demo code for the Arduino and other microcontrollers and
languages in the Resources section of the 28017 product page at www.parall ax.com.
