copyright ? parallax inc. mma7455 3-axis accelerometer module (#28526) v1.1 9/24/2009 page 1 of 6 web site: www.parallax.com forums: forums.parallax.com sales: sales@parallax.com technical: support@parallax.com office: (916) 624-8333 fax: (916) 624-8003 sales: (888) 512-1024 tech support: (888) 997-8267 mma7455 3-axis accelero meter module (#28526) general description the freescale semiconductor mma7455l 3-axis digital output accelerometer is a low power, micro-machined sensor capable of measuring acceleration along its x, y, and z axes. it offers several convenient integrated features including an analog to digital converter (adc), digital low-pass filter, and selectable sensitivity ranges of 2g, 4g, or 8g. this device can be easily configured to detect quick motion pulses as single-taps, double-taps, and 0g (free-fall) conditions on any or all axes and provides configurable interrupt pins (int1 and int2) for each type of event. flexibility and compatibility are designed into this module. an on-board voltage regulator and i/o voltage level-shifters make this module especially easy to connect to virtually any microcontroller. it operates over a wide range of supply voltages from 2.5 vdc to 5.5 vdc and communicates via serial peripheral interface (spi) or inter-integrated circuit (i 2 c) bus. features ? wide input voltage range ? digital output (spi/i 2 c) ? selectable sensitivity: 8-bit mode (2g/4g/8g) or 10-bit mode (8g) ? user-configurable interrupts (int1/int2) ? user-settable registers for calibrating each axis ? low current operation ? compact, 8-pin dip breadboard-friendly package: 0.5? x 0.6? (12.7 x 15.2 mm) application ideas ? inertial measurement units ? tilt sensing for remote control systems ? single-tap or double-tap user input ? multi-axis vibration measurement ? free-fall detection ? motion sensing and data logging ? model airplane flight stabilization key specifications ? power requirements: 2.5 ? 5.5 vdc; 26 a standby, 0.5 ? 3 ma active ? communication: spi or i 2 c ? dimensions: 0.5 x 0.6 x 0.46 in (12.7 x 15.2 x 11.7 mm) ? operating temperature: -40 to +185 f (-40 to +85 c) note: demonstration software files may be downloaded from the 28526 product page at www.parallax.com.
copyright ? parallax inc. mma7455 3-axis accelerometer module (#28526) v1.1 9/24/2009 page 2 of 6 package and pin descriptions absolute maximum ratings note: these are conditions beyond which permanent device damage may occur; it is not implied that the device will function properly throughout this ra nge. for operational ranges, see the operating conditions section below. parameter min typ max unit v in (measured from gnd) 0 -- 6.5 v storage temperature -40 -- +125 c data pin input voltage -0.5 -- v in + 0.5 v pin current -50 -- +50 ma maximum acceleration (all axes) -- -- 5000 g pin # pin name description pin type 1 vin input supply voltage power 2 n/c not connected ? reserved for future use n/a 3 int1 interrupt 1/data ready output 4 int2 interrupt 2 output 5 gnd ground power 6 cs chip select - spi enable (0), i 2 c enable (1) input 7 data i 2 c serial data (sda), spi serial data (sdi/sdo) input/output 8 clk i 2 c serial clock (scl), spi serial clock (spc) input +x +y +z
copyright ? parallax inc. mma7455 3-axis accelerometer module (#28526) v1.1 9/24/2009 page 3 of 6 operating conditions parameter min typ max unit v in supply voltage 2.5 3.3 ? 5 5.5 v supply current (1) operational (sensing) mode (1)(2) -- 437 555 a operational mode & pins loaded (1)(3) -- <3 4.3 ma standby mode (1)(4) -- 26 42 a operating temperature range -40 25 85 c output data (measurement) rate data rate is 125 hz when 62.5 hz bw selected -- 125 -- hz data rate is 250 hz when 125 hz bw selected -- 250 -- hz sensitivity (5) 2g range, 8-bit 58 64 70 count/g 0g output signal (5) 2g range, 8-bit -21 0 21 count spi clock frequency -- 4 -- mhz notes: 1. supply current measured flowing into vin pin. v in = 5.5 v 2. operational mode current measured with mma7455l devic e placed in measurement mode and clk, data, and cs pins disconnected. 3. operation mode & pins loaded is measured as worst-case current draw with cl k, data, and cs pins all connected to ground; int1 and int2 pins left disconnected. 4. standby mode current measured with mma7455l device pl aced in standby mode and clk and data lines left high (connected to v in ) or disconnected. value may be higher if these lines are loaded. 5. values taken from freescale se miconductor mma7455l devic e specifications. principle of operation the freescale mma7455l is a surface-machined micro electro-mechanical system (mems) formed by masking and etching semiconductor ma terials. it can be visualized as a very small mass suspended in the center of the device by tiny springs. when an acceleration is applied to the device, the mass deflects along one or more axes inside the device. built-in ci rcuitry constantly measures the amount of deflection along each axis and translates it into acceleration da ta. then the data becomes available to be read by an external microcontroller. for more detailed information refer to the freescale mma7455l product documentation. i/o level shifting part of what makes this 3-axis accelerometer module so useful is its wide power supply and i/o voltage compatibility range of 2.5 v to 5.5 v. the mma7455l device operates over a supply voltage range of 2.4 v to 3.6 v; so to make it compat ible with devices operating up to 5.5 v, a 3.3 v low dropout (ldo) voltage regulator was installed, as we ll as two types of level shifting ci rcuits. this allows the device to operate and communicate over the full voltage supply range. for the data pin, a bi-directional level shifting ic is used to translate the lower i/o voltage of the mma7455l to the possibly higher voltage used by an ex ternally connected device. this particular level shifter has built-in pull-up resistors to each supply ra il so it can be driven by open drain outputs for i 2 c; but can also be driven low/high for spi protocol. a dditionally, it automatically detects the direction of data flow and switches the output drivers accordingly. the clk and cs pins operate exclusively as inputs, so simpler and cheaper level shifting circuits can be used. only a resistor and schottky diode are required for each pin. see the module schematic section for details. when an external device drives the clk or cs pin low, the i/o pin on the mma7455l is pulled
copyright ? parallax inc. mma7455 3-axis accelerometer module (#28526) v1.1 9/24/2009 page 4 of 6 down through the schottky diode to about 0.35 v. this is plenty low enough to be read as a logic low (0) by the mma7455l accelerometer device. when the cl k or cs pin is driven high or left floating, it gets pulled up to the local v cc by the 2.2k ? resistor. meanwhile, the diod e prevents the possibility of higher external voltages damaging the input pin on the mma7455l. measured acceleration output values the mma7455l converts a detected acceleration into a number which can easily be read by an external microcontroller. the number it generates depends on the sensitivity of the device which can be 2g, 4g, or 8g. one g represents the acce leration due to the earth?s gravity: 1g 9.8m/s 2 or 1g 32.2ft/s 2 . of course this value varies depending on the object?s latitude and distance from sea level. from a sensory standpoint, there is no dete ctable difference between forces observed under the influence of acceleration and forces observed under the influence of gravity. using units of g?s is simply a convenient way of relating the magnitude of a measur ed acceleration to the familiar force of gravity. the full measurement range is divided up into a number of counts which is determined by the number of bits specified for the data; 8-bit da ta has 256 counts, and 10-bit data ha s 1,024 counts. the value of one count, or least significant bit (lsb) of data, can be determined as follows: counts of number range - g full lsb one = so for a sensitivity range of 2g (full range = 4g) in 8-bit mode (256 counts), the value of one lsb would be approximately: count g 0.016 counts 256 4g lsb one = a few key numerical output values over each acce leration range for 8-bit data are shown below for reference. sensitivity range acceleration output value (hex/decimal) -2g $81 -127 -1g $c1 -63 0g $00 0 +1g $3f 63 2g +2g $7f 127 -4g $81 -127 -1g $e1 -31 0g $00 0 +1g $1f 31 4g +4g $7f 127 -8g $81 -127 -1g $f1 -15 0g $00 0 +1g $0f 15 8g +8g $7f 127
copyright ? parallax inc. mma7455 3-axis accelerometer module (#28526) v1.1 9/24/2009 page 5 of 6 module schematic quick start guide the following is a very basic procedure to get starte d initializing and reading values from the digital 3- axis accelerometer module. all the features of th e mma7455l accelerometer are covered in full detail in the freescale semiconductor mma7455l device datasheet. example test code as well as more advanced code demonstrations of this device for the propelle r and basic stamp can be found on the 28526 product page at www.parallax.com. 1. with main power off, make the proper co nnections between the accelerometer and a microcontroller as shown below according to whether spi or i 2 c is used. the voltage connected to the vin pin should be the same as the voltage powering the microcontroller communicating with the device. the value of the pull-up resistors used in i 2 c mode depend on the desired data rate, and the total capacitance of the bus. a reason able starting value for each pull-up resistor is 4.7k ? . this value may need to be reduced if ma ny devices are connected on the bus (which increases the bus capacitance), or if high data rates are required.
copyright ? parallax inc. mma7455 3-axis accelerometer module (#28526) v1.1 9/24/2009 page 6 of 6 2. power on the device and initialize the ?mode control? register ($16 mctl). for example: writing a value of $25 (%00100101) configures the device for spi 3-wire mode, 2g measurement range, and puts the device in measurement mode ra ther than its default standby mode. refer to the mma7455l device datasheet for information on proper spi or i 2 c communication protocol to send and receive data. 3. the device is ready to be read by the microcontro ller. be sure to read from the correct data registers depending on whether 8-bit (2g, 4g, 8g) or 10-bit (8g) data is used. for example: reading the xout8 ($06) data register returns the 8-bit value for acceleration along the x-axis. continue reading data from any other desired axes (yout8, or zout8). this operation can be performed in a continuous loop in software, or intermittently when required by the application. module dimensions see pdf attached.
notes 1. this drawing is inteded for customer reference only. 2. dimensions and board layout are subject to change without notice. material: --- .22 5.59 .50 12.70 .100 2.54 actual size .50 12.70 .60 15.24 .050 1.27 .250 6.35 accelerometer position on circuit board. title mma7455 3-axis accelerometer parent part # --- rev a part # 28526 sheet 1 of 1 drawn by k. mccullough scale: 3:1 date 20090813 www.parallax.com (916) 624-8333 599 menlo drive rocklin, ca 95765 dimensions are in inches (mm) length tolerances: x.xx 0.020 in x.xxx 0.005 in angle tolerances: x 10 x.x 5 unless otherwise specified the information contained in this drawing is the sole property of parallax, inc. any reproduction in part or in whole without the written permission of parallax, inc. is prohibited. proprietary information
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