Download Force Sensitive Resistor (FSR) Sensor Lab

Force Sensitive Resistor (FSR) Sensor Lab
This document gives a generic background of Force Sensitive Resistor (FSR) sensors, and explains how to use an FSR
sensor with the NI myDAQ.
Background:
Force Sensing Resistors (FSR) are a polymer thick film (PTF) device which exhibits a decrease in resistance with an
increase in the force applied to the active surface. Its force sensitivity is optimized for use in human touch control of
electronic devices. FSRs are not a load cell or strain gauge, though they have similar properties. FSRs are not suitable
for precision measurements. [1] The force vs. resistance characteristic shown in Figure 1 provides an overview of FSR
typical response behaviour and a diagram of the sensor. For interpretational convenience, the force vs. resistance
data is plotted on a log/log format. For Further details see [1].
Figure 1
To make some basic measurements and evaluate the device the FSR can configured as part of a simple potential
divider circuit as shown in Figure 2. The op amp buffer circuit although good practice is not required for this
experiment. The graph shows typical output responses for a range of resistor values.
Figure 2
Equipment:
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NI myDAQ
NI LabVIEW
Range of resistors
FSR (http://www.sparkfun.com/products/9673)
Wires/Connections
Set Up Hardware:
The FSR sensor is connected to the myDAQ through four ports--AI1+, AI1-, the +5V power supply, and ground (can
be analog or digital). Wire the sensor to match the figure shown below.
Figure 3: FSR sensor connection to the NI myDAQ
The wires marked red, black and green, purple are the sensor’s power, ground and signal wires, respectively. These
wires may need to be wrapped around more sturdy wires in order for them to connect with the breadboard or screw
terminals. AI 1+/- will be used to read the voltage from the sensor that indicates the force applied.
Software Instructions:
Open 'FSR sensor.vi'. This VI simply reads in the voltage produced from the potential divider circuit formed by the
FSR and resistor (RM) and displays it on a waveform chart. Once the hardware is all set up and your myDAQ
plugged into your computer, run the program.
Using your finder gently place pressure on the sensor, watching the voltage rise and drop.
Figure 4: Front panel of 'FSR sensor.vi'
Figure 5: Block diagram of 'proximity sensor.vi'
Additional Lab work:
Once you have completed the lab and fully understand the operation of your program continue with the following.
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Set a high level detection system - when the voltage goes above a predefined level set an alarm. This could be an
indicator on your front panel or an LED interfaced through the myDAQ.
Take the average of the last 3 measured voltages and display this along with the current instantaneous voltage reading.
Use the instantaneous FSR sensor reading to vary the frequency of an audio signal which is sent to the myDAQ audio
output. The more force that is applied to the sensor the higher the frequency output.
Explore the other analogue sensors provided (Accelerometer and Light Dependant Resistor)
Software Instructions:
References
[1] http://www.sparkfun.com/datasheets/Sensors/Pressure/fsrguide.pdf