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Silicon Designs, Inc. ! 1445 NW Mall Street, Issaquah, WA 98027-5344 ! Phone: 425-391-8329 ! Fax: 425-391-0446
web site: www.silicondesigns.com
[page 9]
Mar 07
THRESHOLD DETECTION CIRCUIT
APPLICATION NOTE
Model 1010 Digital Accelerometer
ACCELERATION THRESHOLD DETECTION:
For applications where it is desired to know when acceleration has exceeded a threshold value, the simple circuit shown
in the schematic (below) can be used. This circuit uses a 74HC161 synchronous binary counter to detect when the DIR
logic output goes high for a minimum of 16 clock cycles in a row. The 74HC74 D-type flip/flop is connected in a "ones-
catch" configuration so that once the threshold is exceeded, the flip/flop stores the event. The clear input sets the counter
value to zero and clears the flip/flop, making the circuit ready to detect the next 16 ones in a row sequence. When driven
by the DIR (true) output, this circuit provides a threshold of approximately 7/8ths of full scale (+43.75g for a ±50g device).
Negative acceleration pulses can be detected by connecting the counter to DIR
___
instead of DIR.
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