ACCELEROMETER:-

An accelerometer is an electromechanical device that will measure acceleration forces.

These forces may be static, like the constant force of gravity pulling at your feet,

or they could be dynamic - caused by moving or vibrating the accelerometer.By

measuring the amount of static acceleration due to gravity, you can find out the

angle the device is tilted at with respect to the earth. By sensing the amount of

dynamic acceleration, you can analyze the way the device is moving.

At first, measuring tilt and acceleration doesn't seem all that exciting.

However, engineers have come up with many ways to make really useful

products using them. An accelerometer can help your project understand its

surroundings better. Is it driving uphill? Is it going to fall over when it takes

another step? Is it flying horizontally or is it dive bombing your professor? A

good programmer can write code to answer all of these questions using the data

provided by an accelerometer. An accelerometer can help analyze problems in

a car engine using vibration testing, or you could even use one to make a

musical instrument. In the computing world, IBM and Apple have recently

started using accelerometers in their laptops to protect hard drives from

damage. If you accidentally drop the laptop, the accelerometer detects the

sudden freefall, and switches the hard drive off so the heads don't crash on the

platters. In a similar fashion, high g accelerometers are the industry standard way of detecting car crashes and deploying airbags at just the right time.

There are many different ways to make an accelerometer! Some accelerometers

use the piezoelectric effect - they contain microscopic crystal structures that get

stressed by accelerative forces, which causes a voltage to be generated. Another

way to do it is by sensing changes in capacitance. If you have two

microstructures next to each other, they have a certain capacitance between

them. If an accelerative force moves one of the structures, then the capacitance

will change. Add some circuitry to convert from capacitance to voltage, and you

will get an accelerometer. There are even more methods, including use of the

piezoresistive effect, hot air bubbles, and light.

ACCELEROMETER PROPERTIES:-

Analog vs digital - First and foremost, you must choose between an

accelerometer with analog outputs or digital outputs. This will be determined

by the hardware that you are interfacing the accelerometer with. Analog style

accelerometers output a continuous voltage that is proportional to

acceleration. E.g. 2.5V for 0g, 2.6V for 0.5g, 2.7V for 1g. Digital

accelerometers usually use pulse width modulation (PWM) for their output.

This means there will be a square wave of a certain frequency, and the amount

of time the voltage is high will be proportional to the amount of acceleration.

Number of axis - For most projects, two is enough. However, if you want to

attempt 3d positioning, you will need a 3 axis accelerometer, or two 2 axis ones

mounted at right angles.

Maximum swing - If you only care about measuring tilt using earth's gravity, a

±1.5g accelerometer will be more than enough. If you are going to use the

accelerometer to measure the motion of a car, plane or robot, ±2g should give

you enough headroom to work with. For a project that experiences very sudden

starts or stops, you will need one that can handle ±5g or more.

Sensitivity - Generally speaking, the more sensitivity the better. This means that

for a given change in acceleration, there will be a larger change in signal.

Since larger signal changes are easier to measure, you will get more accurate

readings.

Bandwidth - This means the amount of times per second you can take a reliable

acceleration reading. For slow moving tilt sensing applications, a bandwidth of

50Hz will probably suffice. If you intend to do vibration measurement, or

control a fast moving machine, you will want a bandwidth of several hundred

Hz.Impedance/buffering issues - This is by far the single most common source

of problems in projects involving analog accelerometers, because so few

people thoroughly read the required documentation. Both PIC and AVR

datasheets specify that for A-D conversion to work properly, the connected

device must have an output impedance under 10kΩ.

Unfortunately, Analog Devices' analog accelerometers have an output

impedance of 32kΩ. The solution to this is to use a low input offset rail to rail

op amp as a buffer to lower the output impedance. As far as we know, the DE-

ACCM is the only accelerometer solution that takes care of this problem for you

FEATURES:- 3-axis sensing Small, low profile package 4 mm × 4 mm × 1.45 mm

LFCSP

Low power : 350 μA (typical)

Single-supply operation: 1.8 V to 3.6 V

10,000 g shock survival

Excellent temperature stability

BW adjustment with a single capacitor per axis

APPLICATIONS:-

Cost sensitive, low power, motion- and tilt-sensing applications in

Mobile devices

Gaming systems

Disk drive protection

Image stabilization

Sports and health devices

crash detector in airbag

50g with 100’s bandwidth.

reliability is of vital importance.

self-test mechanism is mandatory.

- active suspensions

- anti-lock braking systems

- traction control systems

- inertial navigation systems.

integrate twice to obtain the position.

resolution ~ µg to ensure the accuracy over a long period of time.

thermal behavior is extremely important.

Measuring acceleration and tilt:-

Sensitivity and accuracy:-

Here are some typical sensitivity values for common operating voltages:

Operating voltage Sensitivity

3.6V 360 mV/g

3.33V

(default when using onboard regulator)

333 mV/g

3.0V 300 mV/g

2.0V 195 mV/g

Due to manufacturing variances when Analog Devices makes their

accelerometer chips, these values aren’t always set in stone. Sensitivity can

vary by up to 10% in extreme cases, and the 0g bias point can vary up to 5% on

the X and Y axes, and 10% on the Z axis. For projects that require a very high

degree of accuracy, we recommend that you incorporate measured calibrations

into your hardware/software.

Performance features:-

Output buffers:-

A bare accelerometer chip has an output impedance of 32kΩ, which is

unsuitable for obtaining reliable measurements when connected to an analog to

digital converter. On the DE-ACCM3D, a quad rail to rail operational

amplifier buffers the outputs from the ADXL330, greatly reducing output

impedance. The absolute maximum load beyond which accuracy begins to

seriously suffer is 3.3mA, or 500Ω.

Supply filtering:-A 1uF ceramic bypass capacitor on the DE-ACCM3D provides excellent power

supply decoupling. No external capacitors are necessary between Vcc and

GND.

Output filtering and noise:-A pair of 10nF capacitors limit the noise figure of the DE-ACCM3D, without

overly sacrificing bandwidth. RMS noise is typically 7.3mg, and output

bandwidth is 500Hz - making it suitable for high frequency sampling of

acceleration.

Regulator Bypass:-Most people will want to power DE-ACCM3D using the onboard 3.3V

regulator. However, if you are designing an application that needs a lower

operating voltage, you can bypass the voltage regulator.

To do this, use the GND pin as normal. For the positive supply, solder a wire to

the exposed pad labeled BYP. The onboard 1uF capacitor will still be in

parallel with the accelerometer chip, so additional capacitance is not necessary

unless running from a noisy source.

This would be useful for e.g. an application powered directly by 2 AA batteries or a lithium coin battery.

The minimum operating voltage when using bypass mode is 2.0V and the absolute maximum voltage that can be applied when bypassing the regulator is 3.6V.

Powering external devices:-It is possible to use the DE-ACCM3D’s voltage regulator to power external

devices that require 3.3V, such as a low voltage microcontroller. These devices

must be extremely low power so as to not overload the regulator! The maximum

current that can be drawn in this way is 50mA, but ideally you should try keep

things below 10mA. This diagram shows how to connect up an example

microcontroller and all 3 axes.

Additional capacitance across the microcontroller’s power pins may be necessary, depending on your particular setup.

Protection features:-Reverse voltage:-In the event that you mix up VCC and GND, a P channel MOSFET will prevent

current from flowing – protecting the DE-ACCM3D from damage. This

protection is only designed to work with DC voltages. Do not apply AC voltages

to the power pins.

Output shorting:-

The operational amplifier driving the DE-ACCM3D’s outputs is capable of

handling a direct short from the X, Y and Z outputs to ground for as long as you

want.

THEORY OF OPERATION:-

The ADXL335 is a complete 3-axis acceleration measurement system. The

ADXL335 has a measurement range of ±3 g minimum. It contains a polysilicon

surface-micromachined sensor and signal conditioning circuitry to implement

an open-loop acceleration measurement architecture. The output signals are

analog voltages that are proportional to acceleration. The

accelerometer can measure the static acceleration of gravity in tilt-sensing

applications as well as dynamic acceleration resulting from motion, shock, or

vibration.

The sensor is a polysilicon surface-micromachined structure built on top of a

silicon wafer. Polysilicon springs suspend the structure over the surface of the

wafer and provide a resistance against acceleration forces. Deflection of the

structure is measured using a differential capacitor that consists of independent

fixed plates and plates attached to the moving mass. The fixed

plates are driven by 180° out-of-phase square waves. Acceleration deflects the

moving mass and unbalances the differential capacitor resulting in a sensor

output whose amplitude is proportional to acceleration. Phase-sensitive

demodulation techniques are then used to determine the magnitude and

direction of theacceleration. The demodulator output is amplified and brought

off-chip through a 32 kΩ resistor. The user then sets the signal bandwidth of

the device by adding a capacitor. This filtering improves measurement

resolution and helps prevent aliasing.

MECHANICAL SENSOR:-

The ADXL335 uses a single structure for sensing the X, Y, and Z axes. As a

result, the three axes’ sense directions are highly orthogonal and have little

cross-axis sensitivity. Mechanical misalignment of the sensor die to the package

is the chief source of cross-axis sensitivity. Mechanical misalignment can, of

course, be calibrated out at the system level.

PERFORMANCE:-

Rather than using additional temperature compensation circuitry, innovative

design techniques ensure that high performance is built in to the ADXL335. As

a result, there is no quantization error or nonmonotonic behavior, and

temperature hysteresis is very low (typically less than 3mg over the −25°C to

+70°C temperature range).

APPLICATIONS INFORMATION POWER SUPPLY DECOUPLING:-

For most applications, a single 0.1 μF capacitor, CDC, placed close to the

ADXL335 supply pins adequately decouples the accelerometer from noise

on the power supply. However, in applications where noise is present at the

50 kHz internal clock frequency (or any harmonic thereof), additional care

in power supply bypassing is required because this noise can cause errors

in acceleration measurement. If additional decoupling is needed, a 100 Ω

(or smaller) resistor or ferrite bead can be inserted in the supply line. Additionally, a larger bulk bypass capacitor (1 μF or greater) can be added

in parallel to CDC. Ensure that the connection from the ADXL335 ground

to the power supply ground is low impedance because noise transmitted

through ground has a similar effect to noise transmitted through VS.

3-Terminal 1A Positive Voltage Regulator:-

Features:-

• Output Current up to 1A

• Output Voltages of 5, 6, 8, 9, 10, 12, 15, 18, 24V

• Thermal Overload Protection

• Short Circuit Protection

• Output Transistor Safe Operating Area Protection

Description:-

The KA78XX/KA78XXA series of three-terminal positive regulator are

available in the TO-220/D-PAK package and with several fixed output

voltages, making them useful in a wide range of applications. Each type

employs internal current limiting, thermal shut down and safe operating area

protection, making it essentially indestructible. If adequate heat sinking is

provided, they can deliver over 1A output current. Although designed primarily

as fixed voltage regulators, these devices can be used with external components

to obtain adjustable voltages and currents.

T0-220

D-PAK

INTRNAL BLOCK DIAGRAM:-