Introduction
The FlexiForce A201 force sensor is an ultra-thin, flexible printed circuit. The force sensors are constructed of two layers of substrate (polyester/polyimide) film. On each layer, a conductive material (silver) is applied, followed by a layer of pressure-sensitive ink. Adhesive is then used to laminate the two layers of substrate together to form the force sensor. The active sensing area is defined by the silver circle on top of the pressure sensitive ink. Silver extends from the sensing area to the connectors at the other end of the sensor, forming the conductive leads. A201 sensors are terminated with male square pins, allowing them to be easily incorporated into a circuit.
The FlexiForce single element force sensor acts as a force sensing resistor in an electrical circuit. When the force sensor is unloaded, its resistance is very high. When a force is applied to the sensor, this resistance decreases. The resistance can be read by connecting a multimeter to the outer two pins, then applying a force to the sensing area. In the image below, the plot shows both the Force vs. resistance and Force vs. conductance (1/R). Note that the conductance curve is linear, and therefore useful in calibration.
Specifications:
- Thickness: 0.208mm
- Length: 203mm Width: 14mm
- Sensing Area: 9.53mm (diameter)
- Response Time < 5 microseconds
- Operating Temperatures: -9oC to 60oC
- Force Range: 0-25lbs
- Sensor resistance at no load > 5M ohm
In this tutorial, you will going to learn on how to display the voltage level on 2×8 LCD and light up the LED based on the voltage level as the different force exerted to the Flexiforce Sensors(A201). You can refer the data sheet(attachment) before starting this tutorial.
Hardware and Accessories












Getting Started
Part 1: BBFuino with Flexiforce Sensors(A201)
1. A cutter used to cut the 2×40 header pin (Male) into 2×8 ways. The pins was soldered to the 2×8 LCD as shown below.

Figure 1: Soldering the header pins onto the 2×8 LCD
2. A 2×40 header pins (Female) was cutting into 2×8 ways and being soldered onto the LCD pad (DS3) of BBFuino board as shown below.

Figure 2: Soldering the header pin onto the BBFuino Board
3. Soldered the JP8 on the BBFuino as shown below in order the LCD backlight can be function properly.

Figure 3: Soldering the JP8 on the BBFuino board
4. The 2×8 LCD with 2×8 ways of header pin was plug in into the BBFuino board and fit them to a breadboard as shown below.
Figure 4: 2×8 LCD plug to the BBFuino board and fit them to a breadboard
5. Measured the resistance for the flexiforce sensors as it is unloaded and exert a large force to the sensor for the purpose of choosing a suitable resistor for voltage divider.

Figure 5: The resistance of Flexiforce Sensors(A201) as different forced exerted on it.
6. Connect the circuit as the schematic provided as below.

Note: The Op Amp such as LM324 can be used in here in order to amplify the output voltage. If the max output was low, LM324 will amplify the voltage level of the the output voltage to 5V by adjusting the Op Amp gain.The gain of the Op Amp can be calculated by A = 1 + (Rf/Rs).





Part 2: SK28A with Flexiforce Sensors(A201)
1. Repeat the step 1 to step 4 in section Part 1.
2 Next, connect the circuit as the schematic provided.

Note: The Op Amp such as LM324 can be used in here in order to amplify the output voltage. If the max output was low, LM324 will amplify the voltage level of the the output voltage to 5V by adjusting the Op Amp gain.The gain of the Op Amp can be calculated by A = 1 + (Rf/Rs).
3) The following show the some part of the sample source code.. The micro-controller used for this tutorial is PIC16F876A. The MPlab X version 1.20 and XC8 compiler version 1.0 can be downloaded from here Please refer to here for MPlab X tutorial main function: It will obtain the analog value and display it as decimal on the LCD. At the same time, Led will be turn on according to the voltage level.



The tutorial ends here…
Attachment BBFuino_Flexiforce_Sensor_A201_.zip SK28A_Flexiforce Sensor(A201).X.zip
1 thought on “Method on interfacing and use the Flexiforce Sensors(A201)”
I’ve tried the circuit and coding given..but it didn’t works,little help please