Marco H. / Mbed 2 deprecated Piezo_Force_Sensor

Use a piezoelectric sensor as a force detecting endstop switch. Analog input is smoothed using a moving average filter. Connect the piezo sensor parallel with a 1-10 MOhm resistor and 10-47nF capacitor to the analog input.

Dependencies:   mbed

main.cpp@2:c2ed639b8034, 2016-03-08 (annotated)

Committer:
droelf25
Date:
Tue Mar 08 20:02:22 2016 +0000
Revision:
2:c2ed639b8034
Parent:
1:81b6cfb6b112 
.

Who changed what in which revision?

UserRevisionLine numberNew contents of line
droelf25 0:09e2c587fd7b 1 #include "mbed.h"
droelf25 0:09e2c587fd7b 2
droelf25 1:81b6cfb6b112 3 #define TRIGGER_VOLTAGE_MV 1450
droelf25 2:c2ed639b8034 4 #define USE_HYSTERESIS //comment this out to use a debounce delay instead of hysteresis
droelf25 1:81b6cfb6b112 5 #define HYSTERESIS_TRESHOLD_MV 500 //Sensor voltage has to drop below this value to enable next signal. Should prevent multiple triggers caused by voltage fluctuations
droelf25 0:09e2c587fd7b 6 #define FILTER_SAMPLES 5
droelf25 0:09e2c587fd7b 7 #define SIGNAL_LENGTH_MS 10
droelf25 1:81b6cfb6b112 8 #define DEBOUNCE_WAIT_MS 300 //only used when hysteresis is not enabled. Wait a fixed amount of milliseconds to prevent multiple triggers
droelf25 0:09e2c587fd7b 9
droelf25 0:09e2c587fd7b 10 AnalogIn sensor(A0);
droelf25 0:09e2c587fd7b 11 DigitalOut led(LED1);
droelf25 1:81b6cfb6b112 12 DigitalOut signal(D2);
droelf25 1:81b6cfb6b112 13 //InterruptIn user(USER_BUTTON); //no user button on Nucleo F303K8
droelf25 0:09e2c587fd7b 14
droelf25 0:09e2c587fd7b 15 short buffer[FILTER_SAMPLES];
droelf25 0:09e2c587fd7b 16 short bufferPos= 0;
droelf25 0:09e2c587fd7b 17
droelf25 0:09e2c587fd7b 18 short flashCounter = 0;
droelf25 0:09e2c587fd7b 19
droelf25 0:09e2c587fd7b 20 bool isInitialized = false;
droelf25 0:09e2c587fd7b 21 bool isReady = true;
droelf25 1:81b6cfb6b112 22 bool hysteresis = false;
droelf25 0:09e2c587fd7b 23
droelf25 0:09e2c587fd7b 24 Ticker ledFlasher;
droelf25 0:09e2c587fd7b 25 Timeout signalTimeout;
droelf25 0:09e2c587fd7b 26 Timeout debounceTimeout;
droelf25 0:09e2c587fd7b 27
droelf25 0:09e2c587fd7b 28 void flashLED()
droelf25 0:09e2c587fd7b 29 {
droelf25 0:09e2c587fd7b 30 if(flashCounter++ > 30)
droelf25 0:09e2c587fd7b 31 ledFlasher.detach();
droelf25 0:09e2c587fd7b 32
droelf25 0:09e2c587fd7b 33 led = !led;
droelf25 0:09e2c587fd7b 34 }
droelf25 0:09e2c587fd7b 35
droelf25 0:09e2c587fd7b 36 void reset()
droelf25 0:09e2c587fd7b 37 {
droelf25 0:09e2c587fd7b 38 isReady = true;
droelf25 0:09e2c587fd7b 39 }
droelf25 0:09e2c587fd7b 40
droelf25 0:09e2c587fd7b 41 void endSignal()
droelf25 0:09e2c587fd7b 42 {
droelf25 0:09e2c587fd7b 43 led = 0;
droelf25 0:09e2c587fd7b 44 signal = 0;
droelf25 0:09e2c587fd7b 45 }
droelf25 0:09e2c587fd7b 46
droelf25 0:09e2c587fd7b 47 void startSignal()
droelf25 0:09e2c587fd7b 48 {
droelf25 0:09e2c587fd7b 49 led = 1;
droelf25 0:09e2c587fd7b 50 signal = 1;
droelf25 0:09e2c587fd7b 51 signalTimeout.attach_us(&endSignal, 1000 * SIGNAL_LENGTH_MS);
droelf25 1:81b6cfb6b112 52 #ifndef USE_HYSTERESIS
droelf25 1:81b6cfb6b112 53 debounceTimeout.attach_us(&reset, 1000 * DEBOUNCE_WAIT_MS);
droelf25 1:81b6cfb6b112 54 #endif
droelf25 0:09e2c587fd7b 55 }
droelf25 0:09e2c587fd7b 56
droelf25 0:09e2c587fd7b 57 short getAverageVoltage()
droelf25 0:09e2c587fd7b 58 {
droelf25 0:09e2c587fd7b 59 short sum;
droelf25 0:09e2c587fd7b 60 for (int i = 0; i < FILTER_SAMPLES; i++)
droelf25 0:09e2c587fd7b 61 sum += buffer[i];
droelf25 0:09e2c587fd7b 62
droelf25 0:09e2c587fd7b 63 return sum / FILTER_SAMPLES;
droelf25 0:09e2c587fd7b 64 }
droelf25 0:09e2c587fd7b 65
droelf25 0:09e2c587fd7b 66 int main()
droelf25 0:09e2c587fd7b 67 {
droelf25 0:09e2c587fd7b 68 if(!isInitialized) {
droelf25 0:09e2c587fd7b 69 isInitialized = true;
droelf25 0:09e2c587fd7b 70 led = 0;
droelf25 0:09e2c587fd7b 71 signal = 0;
droelf25 0:09e2c587fd7b 72 ledFlasher.attach(&flashLED, 0.03f);
droelf25 1:81b6cfb6b112 73 //user.mode(PullDown);
droelf25 1:81b6cfb6b112 74 //user.fall(&startSignal);
droelf25 0:09e2c587fd7b 75 }
droelf25 0:09e2c587fd7b 76
droelf25 0:09e2c587fd7b 77 while(1) {
droelf25 0:09e2c587fd7b 78 buffer[bufferPos++] = sensor.read() * 3300;
droelf25 0:09e2c587fd7b 79
droelf25 0:09e2c587fd7b 80 if(bufferPos == FILTER_SAMPLES)
droelf25 0:09e2c587fd7b 81 bufferPos = 0;
droelf25 0:09e2c587fd7b 82
droelf25 1:81b6cfb6b112 83 #ifdef USE_HYSTERESIS
droelf25 1:81b6cfb6b112 84 short voltage = getAverageVoltage();
droelf25 1:81b6cfb6b112 85
droelf25 1:81b6cfb6b112 86 if(voltage <= HYSTERESIS_TRESHOLD_MV)
droelf25 1:81b6cfb6b112 87 hysteresis = false;
droelf25 1:81b6cfb6b112 88
droelf25 1:81b6cfb6b112 89 if(voltage >= TRIGGER_VOLTAGE_MV && !hysteresis) {
droelf25 1:81b6cfb6b112 90 startSignal();
droelf25 1:81b6cfb6b112 91 hysteresis = true;
droelf25 1:81b6cfb6b112 92 }
droelf25 1:81b6cfb6b112 93 #else
droelf25 0:09e2c587fd7b 94 if(isReady) {
droelf25 1:81b6cfb6b112 95 if(getAverageVoltage() >= TRIGGER_VOLTAGE_MV) {
droelf25 0:09e2c587fd7b 96 startSignal();
droelf25 0:09e2c587fd7b 97 isReady = false;
droelf25 1:81b6cfb6b112 98
droelf25 0:09e2c587fd7b 99 }
droelf25 0:09e2c587fd7b 100 }
droelf25 1:81b6cfb6b112 101 #endif
droelf25 0:09e2c587fd7b 102 }
droelf25 0:09e2c587fd7b 103 }