ADXL202/ADXL210

–7–

REV. B

The ADXL202/ADXL210 have provisions for bandlimiting the

implement low-pass filtering for antialiasing and noise reduc-

tion. The equation for the 3 dB bandwidth is:

1

2

π (32 kΩ) × C(x, y)

()

5

µF

as

±25% of its nominal value of 32 kΩ; so the bandwidth will

is required in all cases.

Capacitor

Bandwidth

Value

10 Hz

0.47

µF

50 Hz

0.10

µF

100 Hz

0.05

µF

200 Hz

0.027

µF

500 Hz

0.01

µF

5 kHz

0.001

µF

The period of the DCM output is set for both channels by a

is:

T 2

=

Ω)

125 M

Ω

A 125 k

Ω resistor will set the duty cycle repetition rate to ap-

proximately 1 kHz, or 1 ms. The device is designed to operate at

duty cycle periods between 0.5 ms and 10 ms.

Table II. Resistor Values to Set T2

T2

1 ms

125 k

Ω

2 ms

250 k

Ω

5 ms

625 k

Ω

10 ms

1.25 M

Ω

Ω

and 2 M

Ω when taking the output from X

parasitic capacitance at this node.

Selecting the Right Accelerometer

For most tilt sensing applications the ADXL202 is the most

appropriate accelerometer. Its higher sensitivity (12.5%/g allows

the user to use a lower speed counter for PWM decoding while

maintaining high resolution. The ADXL210 should be used in

applications where accelerations of greater than

±2 g are expected.

MICROCOMPUTER INTERFACES

The ADXL202/ADXL210 were specifically designed to work

with low cost microcontrollers. Specific code sets, reference

designs, and application notes are available from the factory.

This section will outline a general design procedure and discuss

the various trade-offs that need to be considered.

The designer should have some idea of the required perfor-

mance of the system in terms of:

Resolution: the smallest signal change that needs to be detected.

Bandwidth: the highest frequency that needs to be detected.

Acquisition Time: the time that will be available to acquire the

signal on each axis.

These requirements will help to determine the accelerometer

bandwidth, the speed of the microcontroller clock and the

length of the T2 period.

When selecting a microcontroller it is helpful to have a counter

timer port available. The microcontroller should have provisions

for software calibration. While the ADXL202/ADXL210 are

highly accurate accelerometers, they have a wide tolerance for

DEMOD

32k

32k

OSCILLATOR

X SENSOR

Y SENSOR

X OUT

Y OUT

SELF TEST

+3.0V TO +5.25V

COM

T2

C

O

U

N

T

E

R

P

T2

A(

g) = (T1/T2 – 0.5)/12.5%

0

g = 50% DUTY CYCLE

T1

DEMOD

DUTY

CYCLE

MODULATOR

(DCM)

ADXL202/

ADXL210

Figure 13. Block Diagram