Guide

www.flexpoint.com Copyright
©
2015 Flexpoint Sensor Systems Page 7 of 15
A
1
INPUT
A
2
A
3
A
4
A
N-1
A
N
RESET
Bend Sensor
Selection
Channels
Calibration
Channels
C1
R
MIN
R
MAX
Bend Sensor
Bend Sensor
68HC05C4 Microcontroller
Figure 1.4
Multi-Channel Bend Sensor
®
-to-Digital Interface:
Sampling Cycle (any Bend Sensor
®
channel):
The microcontroller switches to a specific Bend Sensor
®
channel, toggling it high, while all other Bend
Sensor
®
channels are toggled low. The RESET channel is toggled high, a counter starts and the
capacitor C1 charges, with its charging rate controlled by the resistance of the Bend Sensor
®
(t~RC).
When the capacitor reaches the high digital threshold of the INPUT channel, the counter shuts off, the
RESET toggles low, and the capacitor discharges.
The number of “counts” it takes from the toggling of the RESET high to the toggling of the INPUT high is
proportional to the resistance of the Bend Sensor
®
device. The resistors R
MIN
and R
MAX
are used to set a
minimum and maximum “counts” and therefore the range of the “counts”. They are also used
periodically to re-calibrate the reference. A sampling cycle for R
MIN
is run, the number of “counts” is
stored and used as a new zero. Similarly, a sampling cycle for R
MAX
is run and the value is stored as the
maximum of the range (after subtracting the R
MIN
value). Successive Bend Sensor
®
samplings are
normalized to the new zero. The full range is “zoned” by dividing the normalized maximum “counts” by
the number of desired zones. This will delineate the window size or width of each zone.
Continual sampling is done to record changes in Bend Sensor
®
resistance due to changes in deflection.
Each Bend Sensor
®
device is selected sequentially.