Datasheet
Simplified Sensor Equivalent Circuit
Recommended sensor read out:
UREF+ High reference voltage
B1 High impedance buffer
R1 Resistor
D1 Diode 1
D2 Diode 2
is connected to a high (VREF+) and a
low (VREF-) reference voltage that is
identical to the reference voltages of
the AD-converter (ADC). The wiper is
connected to the ADC input of the mi-
croprocessor (MPU) through the high-
impedance buffer (B1). The voltage
readings of the ADC are proportional
to the position of the center of gravity
In order to measure the wiper resis-
tance (SR) value, which is dependent
on the pressure applied to the active
high and then to a low voltage for cur-
rent injection through a resistor (R1).
This current causes a voltage change
at the wiper that is proportional to the
SR value. The two diodes (D1 and D2)
make sure that no leakage current from
the digital outputs of the micropro-
measurement.
The digital output state sequence is di-
vided into three or four steps:
1. R1 not connected for position meas-
urement
2. Positive current injection for SR
(pressure) measurement
3. R1 not connected for position meas-
urement (optional, could be omitted)
4. Negative current injection for SR
(pressure) measurement
The voltage measured at the end of
state (2) is temporarily stored in order
to subtract the voltage from state (4)
at the end of this cycle. This voltage
difference is proportional to the FSR-
wiper resistance and inversely propor-
tional to the applied force.
The time delay between output state
switching and ADC sampling must be
long enough for voltage settling in the
circuit capacitors. This delay should be
4 × R1 × CP for the resistance meas-
urement during states (2) and (4), typi-
cally 0.01 to 0.1 ms, where CP is the
total capacitance of the sensor and
the circuit. During the remaining time,
typically 10 ms, the wiper carries no
current (1) and the voltage stabilizes to
a good accuracy for position reading.
The R1 × CP time constant can eas-
ily be determined from the buffer (B1)
output signal, displayed on an oscillo-
scope. The update frequency is a func-
tion of the reaction time, required for
the application. Over-sampling can be
considered for noise suppression by
Linpot Sensor:
E1 Electrode 1 pad
E2 Electrode 2 pad
E3 Electrode 3 pad
CP Parasitic parallel
capacitance of the sen-
sor sandwich
RC1 Conductor resistance of
electrode 1 side
RC2 Conductor resistance of
electrode 2 side
RC3 Conductor resistance of
Electrode 3 side
SR Sensor resistance
RFX1 Resistance X1 of
RFX2 Resistance X2 of
RFIX Resistance of printed
RFIX = RFX1 + RFX2
Linpot
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CIS