- Sensors are physical objects that can detect events and changes in various parameters such as environment, temperature, humidity, and so on. The sensors can generate appropriate output based on the (events or) changes detected. Sensors are classified according to various criteria such as sound, automotive, electrical, chemical, and so on. The most common sensors are pressure, force, proximity, light, heat, temperature, position, and so on.
- The application of sensors in real-time electrical and electronic circuits for developing various innovative projects is rapidly increasing.
- Consider a proximity-based automatic door opening system, which is commonly used in shopping malls, offices, banks, and other public places. Similarly, the use of sensor technology in various fields such as embedded systems, robotics, and so on is rapidly expanding. Let’s talk about the force-sensing resistor in this article.
Force Sensing Resistor
- One of the most common passive components in electrical and electronic circuits is the resistor. A resistor is a circuit element that is used to reduce current flow and lower voltage levels in circuits. Fixed value resistors, variable resistors, wire wound resistors, metal film resistors, and special resistors are all types of resistors that are classified based on various criteria. Pencil resistors, light-dependent resistors, force-sensing resistors, and so on are examples of special-purpose resistors.
- Resistance Calculator using a Simple Resistor Color Code Calculator.
- A force sensing resistor is a type of resistor whose resistance can be adjusted by varying the force or pressure applied to it. Franklin Event off invented and patented the FSR sensor technology in 1977. The FSR sensors are made of a conductive polymer that changes resistance depending on the force applied to its surface. As a result, these are referred to as FSR sensors; the force-sensing resistor is a hybrid of resistor and sensor technology.
- The force sensing resistor is typically supplied as a polymer sheet or ink for screen printing. This sensing film contains both electrically conducting and non-conducting particles. These particles are typically sub-micrometers in size and are designed to reduce temperature dependence while also improving mechanical properties and surface durability.
- When a force is applied to the surface of a sensing film, the particles come into contact with the conducting electrodes, causing the resistance of the film to change. There are several resistive-based sensors, but force-sensing resistors perform well in challenging environments and require a simple interface when compared to other resistive-based sensors.
- Even though there are various types of force sensors, force-sensing resistors have several advantages such as thin size (less than 0.5mm), low cost, and good shock resistance. The only disadvantage of FSR sensors is their low precision; there will be a 10% or greater difference in measurement results.
- Force sensing resistors are called (PTF) polymer thick film devices. The resistance of FSR sensors decreases with an increase in pressure applied to their surface.
4-Simple Steps to Design Force Sensing Resistor
Force sensing resistor can be designed by following the four simple steps shown below.
- Collecting the materials needed to create FSR sensors. Electrical and electronic components, including PCB, conductive foam, wires, solder, hot glue, and tools like a soldering iron, hot glue gun, and cutter, are the materials used to make the FSR sensor.
- The size of FSR sensors varies based on application requirements, consider a PCB cut into two identical square plates and solder plates with the red and black wire as shown in the figure. Then, cut the conducting foam into the same shape and size as the plate.
- Now, connect the two plates and conducting foam by outline glue such that, make sure it conducts well.
- Consequently, a multimeter may be used to test the FSR sensor. If you connect the FSR sensor’s leads to a multimeter without exerting any stress on the force-sensing resistor’s surface, the resistance will be very high. The resistance begins to decrease when force is applied to its surface.
Applications of Force Sensing Resistor
- Force sensing resistors have a wide range of uses in a variety of industries, including foot pronation systems, automobile sensors, resistive touchpads, musical instruments, keypads, portable electronics, and more.
Touch Controlled Load Switch
- The project for a touch-controlled load switch aims to regulate any load with a touch-sensitive switch. The 555 timer, relay, diodes, capacitors, resistors, and load (light) are all used in the project and are connected as indicated in the block diagram.
- Based on the triggering signal obtained from the touch plate, the 555 timers are coupled in monostable mode to drive the relay. The 555 timer’s triggering pin is wired so that it touches the plate. The 555 timer output drives the relay for a set amount of time if the touch plate is activated. The time duration is adjustable using the timer’s RC time constant, and the load automatically turns off after a predetermined amount of time. The touch plate develops voltage using the human body’s induced supply.