1010L-002 Datasheet, PDF (7/9 Pages) List of Unclassifed Manufacturers – DIGITAL ACCELEROMETER

APPLICATION NOTE
Model 1010 Digital Accelerometer
ACCELERATION MEASUREMENT WITH A MICROCONTROLLER:
The CNT (count) pulse density modulation output of the model 1010 accelerometer was designed to drive the type of
hardware pulse counter that is sometimes present in microcontrollers. The schematic (below) shows a model 1010
accelerometer driving the T0 counter of an Intel 80C51 microcontroller. The accelerometer's clock is provided by the
Address Latch Enable (ALE) output of the 80C51 after being divided by a factor of four by the two 74HC74 "D-Type"
flip/flops. The divide by 4 is needed because the maximum count rate of the 80C51's T0 counter is 1/24th of the 8051's
clock oscillator frequency (FOSC) and the frequency of ALE is 1/6th of FOSC. Divisors of greater than four should be used if
FOSC is greater than 12 MHz to keep the accelerometer's clock frequency at or below the recommended 1 MHz maximum.
Use of ALE for the accelerometer clock is only recommended for applications where no external memory is connected to
the 80C51. ALE is missing an output pulse for each MOVX instruction which is used to access external memory.
Alternatively, any available clock source asynchronous with the 8051's clock may be used to drive the accelerometer so
long as its frequency is between 100 kHz and 1 MHz and is no greater than 1/48th of FOSC.
MODEL 1010 CONNECTION TO A MICROCONTROLLER
To obtain each interval's average acceleration, the software needs to poll counter T0's value at fixed intervals then subtract
each new counter value from its previous value to obtain a delta (difference) count for each interval. Of course the software
must also account for wraparound of the counter which requires that the counter contain enough bits to prevent more than
one counter overflow during each sample period. The delta count relates to the average applied acceleration according
to the following equation.
∆C =
f _CLK



1
2
+
A_g


g_SPAN 
f _SR
Where:
∆C
f_CLK
A_g
g_SPAN
f_SR
= the change in the counter’s value over each sample interval
= the accelerometer's input clock frequency
= the average acceleration force in g's during the sample interval
= 2 * (full scale acceleration rating of accelerometer)
= the software sample rate of the counter in samples/sec
At minus full-scale acceleration, the difference count (∆C) is zero. Zero acceleration results in a difference count of one-
half of the maximum difference count value; plus full scale acceleration results in the maximum value (f_CLK / f_SR). The
actual difference value achieved at zero acceleration [which will be near ½(f_CLK / f_SR)], may be subtracted from each
interval's difference count to obtain the acceleration count in sign-magnitude format.
SPECIFICATIONS SUBJECT TO CHANGE WITHOUT NOTICE
Silicon Designs, Inc. ! 1445 NW Mall Street, Issaquah, WA 98027-5344 ! Phone: [phone] ! Fax: [phone]
web site: www.silicondesigns.com
[page 7]
Mar 07