v1.0 Mar 2018 6
Ohmite FSP Series Integration Guide: Force Sensing Potentiometer
Integration Guide
Force Sensing Potentiometer
4 FSP01CE/FSP02CE Connection and Sampling (continued)
4.2 Force Measurement (continued)
The test results from these three methods are shown in Figures 4, 5 and 6 and the test positions are shown in Figure
7. The advantages and disadvantages for the three methods are discussed in Table 1 along with the complexity of the
sampling firmware and hardware required. The best method for the project requirements should be chosen considering a
balance of required force accuracy, electronic complexity and cost.
5 FSP01CE/FSP02CE Recommendations
For the majority of force sensing potentiometer implementations Method 1 is most likely the best compromise. It
is a simple approach electronically and outputs a very liner response to force. Even though it suffers from reduced
resolution at higher forces this is generally not a critical requirement for most applications. Furthermore it’s position
dependency is only relevant for finger forces greater than 200-300g which is sufficient for most applications.
Where increased resolution at higher forces is a requirement in the application Methods 2 or 3 can be employed, and if
high finger force consistency is relevant then Method 3 should be chosen.
Figure 7. Test results for the 3 methods with force measurements
taken at various locations along the FSP (units:mm)
Method Advantages Disadvantages Complexity
1• Less dependent on the
position of the applied
force on the FSLP
than method 2 at low
forces
• Linear relationship
between applied force
and ADC output
• Linearity continues
beyond 1kg finger
force
• Applying force near one end of
the pot where the voltage is high,
results in a different ADC output
comparing to other places on the
POT
• The measured data is noisier at
higher forces (can be resolved
by using an ADC with higher
resolution)
• The need to take two analog
readings can introduce
inaccuracies
2 ADC pins are required. The System
needs some form of averaging in order
to increase the resolution and read
more accurate data. Also, the nature
of the method demands working with
arithmetic and floating points. Hence,
a fast microcontroller (preferably more
than 8Mhz) and relatively complex
hardware is needed.
2• Only one analog
reading is needed,
which make the circuit
simpler and more
accurate
• More stable and
reliable data
• Force output is dependent on the
position of applied force on FSLP
• Force output has an exponential
characteristic and can saturate
beyond 1Kg finger force
Only single ADC pin is needed which
makes both the firmware and the
hardware easy to implement.
3• Produces more stable
and reliable data
• This method is least
dependent on the
position of applied
force
• At higher forces greater than 500g
ADC output becomes dependent
on the position of applied force
on FSLP
• Data has an exponential
characteristic and starts to
saturate beyond 1kg finger force
Two GPIO pins and one ADC pin
are required. Furthermore, the
system needs to constantly toggle
the GPIO pins and use arithmetic
which demands fast microcontroller
(preferably 8Mhz and up) and relatively
complex hardware.
10.00
10.00
123
65.00
10.00
109.00
44.50
10.00
8.00
46.50
1
2
3
Table 1. Advantages and disadvantages of the three methods for measuring the force of an FSP
