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en:examples:sensor:force [2012/06/09 11:03] – raivo.sell | en:examples:sensor:force [2020/07/20 09:00] (current) – external edit 127.0.0.1 | ||
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===== Theory ===== | ===== Theory ===== | ||
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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' | 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' | ||
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===== Practice ===== | ===== Practice ===== | ||
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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. | 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. | ||
- | 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 | + | 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 |
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: | ||
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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. | ||
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<code c> | <code c> | ||
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- | // The demonstration program of the force sensor. | ||
- | // The LCD display shows the measured force (Newtons) and weight (kg). | ||
- | // | ||
#include < | #include < | ||
#include < | #include < | ||
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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; |