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en:examples:sensor:force [2012/06/06 18:21] – raivo.sellen:examples:sensor:force [2020/07/20 09:00] (current) – external edit 127.0.0.1
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 ====== Force sensor ====== ====== Force sensor ======
  
-//Necessary knowledge: [HW] [[en:hardware:homelab:sensor]], [HW] [[en:hardware:homelab:lcd]],  [AVR] [[en:avr:adc]], [LIB] [[en:software:homelab:library:adc]], [LIB] [[en:software:homelab:library:module:lcd_graphic]], [LIB] [[en:software:homelab:library:module:sensor]]//+//Necessary knowledge: [HW] [[en:hardware:homelab:sensor]], [HW] [[en:hardware:homelab:digi]],  [AVR] [[en:avr:adc]], [LIB] [[en:software:homelab:library:adc]], [LIB] [[en:software:homelab:library:module:lcd_graphic]], [LIB] [[en:software:homelab:library:module:sensor]]//
  
 ===== Theory ===== ===== Theory =====
  
-[{{  :examples:sensor:force:09375-1.jpg?250|}}] +[{{  :examples:sensor:force:09375-1.jpg?250|Force-sensing resistor}}] 
-[{{  :en:examples:sensor:forse_sensing_resistor.png?250|}}]+[{{  :en:examples:sensor:forse_sensing_resistor.png?250|Force-sensing resistor layers}}]
  
 FSR (force-sensing resistor) sensor allow you to detect physical pressure, squeezing and weight. FSR is basically a resistor that changes its resistive value (in ohms Ω) depending on how much it’s pressed. These sensors are fairly low cost and easy to use but they're rarely accurate. They also vary some from sensor to sensor perhaps 10%. It means when you use FSR's you should only expect to get ranges of response. As with all resistive based sensors force-sensing resistors require a relatively simple interface and can operate satisfactorily in moderately hostile environments. Compared to other force sensors, the advantages of FSR are their size and good shock resistance. However FSR will be damaged if pressure is applied for a longer time period (hours).  FSR (force-sensing resistor) sensor allow you to detect physical pressure, squeezing and weight. FSR is basically a resistor that changes its resistive value (in ohms Ω) depending on how much it’s pressed. These sensors are fairly low cost and easy to use but they're rarely accurate. They also vary some from sensor to sensor perhaps 10%. It means when you use FSR's you should only expect to get ranges of response. As with all resistive based sensors force-sensing resistors require a relatively simple interface and can operate satisfactorily in moderately hostile environments. Compared to other force sensors, the advantages of FSR are their size and good shock resistance. However FSR will be damaged if pressure is applied for a longer time period (hours). 
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 ===== Practice ===== ===== Practice =====
  
-[{{  :en:examples:sensor:force_conductance_graph.png?250|}}] +[{{  :en:examples:sensor:force_conductance_graph.png?250|Force conductance graph}}] 
-[{{  :en:examples:sensor:force_chematic.png?250|}}]+[{{  :en:examples:sensor:force_chematic.png?250|Voltage divider schematics for the sensor}}]
  
 Pololu FSR with 12.7 mm diameter circular active area are 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. The force vs. resistance characteristic provides an overview of FSR typical response behavior.  For interpretational convenience the force vs. resistance data is plotted on a log/log format. In general, FSR response approximately follows an inverse power-law characteristic (roughly 1/R). Pololu FSR with 12.7 mm diameter circular active area are 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. The force vs. resistance characteristic provides an overview of FSR typical response behavior.  For interpretational convenience the force vs. resistance data is plotted on a log/log format. In general, FSR response approximately follows an inverse power-law characteristic (roughly 1/R).
  
-The easiest way to measure a resistance of FSR is to connect one terminal to power and the other to a pull-down resistor to ground. Then the point between the fixed pull-down resistor and the variable FSR resistor is connected to the analogue input of a Homelab controller board. In this configuration the analogue voltage reading ranges from 0V (ground) to about 5V (or about the same as the power supply voltage). As the resistance of the FSR decreases the total resistance of the FSR and the pull-down resistor decreases from about 100Kohm to 10Kohm. That means the current flowing through both resistors increases which in turn causes the voltage across the fixed 10K resistor to increase. +The easiest way to measure a resistance of FSR is to connect one terminal to power and the other to a pull-down resistor to ground. Then the point between the fixed pull-down resistor and the variable FSR resistor is connected to the analogue input of a Controller board. In this configuration the analogue voltage reading ranges from 0V (ground) to about 5V (or about the same as the power supply voltage). As the resistance of the FSR decreases the total resistance of the FSR and the pull-down resistor decreases from about 100Kohm to 10Kohm. That means the current flowing through both resistors increases which in turn causes the voltage across the fixed 10K resistor to increase. 
  
 Measuring the Newton force by the FSR it is good idea to map analogue voltage reading ranges to 0 V to supply voltage. After that you can calculate the FSR resistance using following formula: Measuring the Newton force by the FSR it is good idea to map analogue voltage reading ranges to 0 V to supply voltage. After that you can calculate the FSR resistance using following formula:
  
-R<sub>FSR</sub> = ((V<sub>cc</sub> - U) * R1) / U+R<sub>FSR</sub> = ( (V<sub>cc</sub> - U) * R1) / U
  
 Where: Where:
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 The example program of the force sensor shows the measured force (Newtons) and weight (kg) on the LCD.  The example program of the force sensor shows the measured force (Newtons) and weight (kg) on the LCD. 
  
-~~PB~~+<pagebreak>
  
 <code c> <code c>
-// 
-// The demonstration program of the force sensor. 
-// The LCD display shows the measured force (Newtons) and weight (kg). 
-// 
 #include <stdio.h> #include <stdio.h>
 #include <homelab/adc.h> #include <homelab/adc.h>
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 #include <homelab/module/lcd_gfx.h> #include <homelab/module/lcd_gfx.h>
  
-// 
 // Map a value from one range to another. // Map a value from one range to another.
-// 
 long map(long x, long in_min, long in_max, long out_min, long out_max) long map(long x, long in_min, long in_max, long out_min, long out_max)
 { {
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 } }
    
-// +// Main program
-// The main program. +
-//+
 int main(void) int main(void)
 { {
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  long force; // The resistance converted to force.   long force; // The resistance converted to force. 
  long weight; // The force converted to weight.   long weight; // The force converted to weight. 
- 
    
  // Set the external sensors pins.  // Set the external sensors pins.
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  // The voltage = Vcc * R / (R + FSR) where R = 10K and Vcc = 5V  // The voltage = Vcc * R / (R + FSR) where R = 10K and Vcc = 5V
-            // so FSR = ((Vcc - V) * R) / V + // so FSR = ( (Vcc - V) * R) / V 
-                // fsrVoltage is in millivolts so 5V = 5000mV+ // fsrVoltage is in millivolts so 5V = 5000mV
  resistance = 5000 - voltage;       resistance = 5000 - voltage;     
          resistance *= 10000; // 10K resistor          resistance *= 10000; // 10K resistor
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  }  }
 } }
- 
 </code> </code>
en/examples/sensor/force.1339006900.txt.gz · Last modified: 2020/07/20 09:00 (external edit)
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