So these are not pure conductor material devices. The FSR here are robust polymer thick film (PTF) devices. Sensitivity of sensor is in conductor numbers.īut in this case the resistance will be decreasing with pressure because the material used here is not a pure conductor. Each of these lines represents a conductor. On looking closely one can sees many lines inside the sensor. This is what happens inside the Force Sensors shown in above figure. For a considerable change many conductors are stacked together. But this change is small compared to overall resistance. So with this for a conductor under pressure or weight the resistance of conductor increases. So by formula the resistance of conductor should increase, as the resistance R is inversely proportional to area and also directly proportional to length l. Now consider a conductor with resistance “R”, if some pressure is applied on top of conductor, the area on conductor decreases and the length of conductor increases as a result of pressure. The resistance of a pure conductor is given by: So when the weight is applied on top of FORCE sensor, the resistance is changed drastically. The resistance of FS400 over weight is shown in below graph:Īs shown in above figure, the resistance between the two contacts of sensor decreases with weight or the conductance between two contacts of sensor increases. the sensor might damage permanently.Īs told earlier this sensor is used to sense the changes in pressure. If weights higher than 1Kg applied the sensor might show some deviations. So keep in mind the driving currents while installing. Also the sensor has a limit on force that is 10Newtons. If the force is applied at wrong times the device could damage permanently.Īnother important thing to know that, the sensor can drive currents of high range. Now it is important to note that the FSR 400 is sensitive along the length, the force or weight should be concentrated on the maze on the middle of eye of sensor, as shown in figure. The picture of FSR400 is shown in below figure. FSR400 is one of the cheapest force sensors in the market. We are going to use one of the cheaper versions because we don’t need much of accuracy here. FORCE sensor is available in different sizes and shapes. To interface a FORCE sensor with ARDUINO UNO, we are going use 8 bit ADC (Analog to Digital Conversion) feature in arduno uno.Ī FORCE sensor is a transducer which changes its resistance when pressure is applied on surface. Now let’s talk about force sensor or weight sensor. So for now we know that, we can control the SERVO MOTOR shaft by varying the duty ratio of PWM signal generated by UNO. This PWM in here is generated by using ARDUINO UNO. This ratio is decoded by control system in servo and it adjusts the position based on it. 1milli second of ‘ON time’ and 17milli second of ‘OFF time’ in a 18ms signal.įor the shaft to be moved to 12o clock the ON time of signal must be 1.5ms and OFF time should be 16.5ms. Based on this DUTY RATION the control electronics adjust the shaft.Īs shown in below figure, for the shaft to be moved to 9o clock the TURN ON RATION must be 1/18.ie. The important thing here is the DUTY RATIO of the PWM signal. The frequency of PWM (Pulse Width Modulated) signal can vary based on type of servo motor. This data regarding position of shaft is sent through the SIGNAL pin. The position data to the control should be sent in the form of PWM signal through the Signal pin of servo motor. The position of the shaft of the DC motor is adjusted by the control electronics in the servo, based on the duty ratio of the PWM signal the SIGNAL pin. Simply speaking the control electronics adjust shaft position by controlling DC motor. The RED wire is connected to power, Black wire is connected to ground and YELLOW wire is connected to signal.Ī servo motor is a combination of DC motor, position control system, gears.
A servo motor will have mainly there wires, one is for positive voltage another is for ground and last one is for position setting. Servo motors are available at different shapes and sizes. Servo motors are also used in some of printers and fax machines. These motors are used in robotic arm machines, flight controls and control systems. These are proposed for low speed, medium torque and accurate position application.
These are not proposed for high speed applications. Servo Motors are used where there is a need for accurate shaft movement or position. Before going any further let’s talk about about the servo and other components. It will be a servo control system where the servo shaft position is determined by the weight present on the force sensor. In this tutorial we will develop a circuit using Force sensor, Arduino Uno and a servo motor.
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