| commit | author | age | ||
| df1f8e | 1 | /* |
| A | 2 | ____ _____ _ _ |
| 3 | | __ )| ____| | / \ | |
| 4 | | _ \| _| | | / _ \ | |
| 5 | | |_) | |___| |___ / ___ \ | |
| 6 | |____/|_____|_____/_/ \_\ | |
| 7 | http://bela.io | |
| 8 | */ | |
| 9 | /** | |
| 10 | \example Sensors/ultrasonic-distance-sensor/render.cpp | |
| 11 | ||
| 12 | Measuring distances with ultrasonic sensors | |
| 13 | --------------------------- | |
| 14 | ||
| 15 | Ultrasonic sensors can detect distances to a high degree of accuracy, even | |
| 16 | in many conditions where infrared sensors would not be suitable (e.g.: when natural | |
| 17 | light is a problem. | |
| 18 | For this example we used the [HC-SR04](https://cdn.sparkfun.com/datasheets/Sensors/Proximity/HCSR04.pdf). | |
| 19 | ||
| 20 | After it receives a short pulse (> 10us) at its TRIGGER input, the module outputs from the | |
| 21 | ECHO output a pulse whose length is proportional to the distance of the object that is in | |
| 22 | front of the sensor. When a trigger is received the module emits an ultrasonic wave | |
| 23 | from its emitter and then receives the signal back in its receiver, measuring the time | |
| 24 | difference between the two. | |
| 25 | ||
| 26 | According to the datasheet of this sensor, the following relation stands: | |
| 27 | time[us] / 58 = distance[cm] | |
| 28 | The dataseheet recommends a minimum interval of 60ms between triggers, in order to be able to | |
| 29 | read the result appropriately. | |
| 30 | ||
| 31 | Bela sends out the TRIGGER event every 2646 samples(60ms) and then waits for a pulse to come | |
| 32 | appear on the ECHO pin. The `PulseIn` class is used here to monitor a digital pin for an HIGH | |
| 33 | pulse and once the pulse termiantes, it returnes the duration ( in samples ) of the pulse. | |
| 34 | ||
| 35 | The module requires a 5V power supply and its digital inputs and outputs are low at 0V and | |
| 36 | HIGH at 5V. Check the pin diagram in the IDE to see where to find the pins you need. | |
| 37 | It is important that the 5V ECHO output from the module *is not* connected | |
| 38 | straight to Bela's digital inputs, as that would most likely kill the Bela board | |
| 39 | (digital I/Os are 3.3V tolerant). You will need to use a passive resistor divider from the | |
| 40 | HC-SR04's ECHO output to scale down the voltage before connecting it to the digital input | |
| 41 | on `gEchoDigitalInPin`. | |
| 42 | ||
| 43 | On the scope you should see the pulses coming in from the trigger and the distance. The closer | |
| 44 | the object, the shorter the pulses. Make sure you set the trigger to "channel 1" (the pulse) and | |
| 45 | you set the horizontal zoom appropriately. | |
| 46 | */ | |
| 47 | ||
| 48 | #include <Bela.h> | |
| 49 | #include <stdlib.h> | |
| 50 | #include <libraries/Scope/Scope.h> | |
| 51 | #include <libraries/PulseIn/PulseIn.h> | |
| 52 | ||
| 53 | PulseIn pulseIn; | |
| 54 | Scope scope; | |
| 55 | int gTriggerInterval = 2646; // how often to send out a trigger. 2646 samples are 60ms | |
| 56 | int gMinPulseLength = 7; //to avoid spurious readings | |
| 57 | float gRescale = 58; // taken from the datasheet | |
| 58 | unsigned int gTrigDigitalOutPin = 7; //channel to be connected to the module's TRIGGER pin - check the pin diagram in the IDE | |
| 59 | unsigned int gEchoDigitalInPin = 7; //channel to be connected to the modules's ECHO pin via resistor divider. Check the pin diagram in the IDE | |
| 60 | int gTriggerCount = 0; | |
| 61 | int gPrintfCount = 0; | |
| 62 | ||
| 63 | bool setup(BelaContext *context, void *userData) | |
| 64 | { | |
| 65 | // Set the mode of digital pins | |
| 66 | // pinMode(context, 0, gTrigDigitalOutPin, OUTPUT); // writing to TRIGGER pin | |
| 67 | // pinMode(context, 0, gEchoDigitalInPin, INPUT); // reading from ECHO pin | |
| 68 | pulseIn.setup(context, gEchoDigitalInPin, HIGH); //detect HIGH pulses on the ECHO pin | |
| 69 | scope.setup(2, context->digitalSampleRate); | |
| 70 | return true; | |
| 71 | } | |
| 72 | ||
| 73 | void render(BelaContext *context, void *userData) | |
| 74 | { | |
| 75 | for(unsigned int n = 0; n < context->digitalFrames; ++n){ | |
| 76 | gTriggerCount++; | |
| 77 | bool state; | |
| 78 | if(gTriggerCount == gTriggerInterval){ | |
| 79 | pinMode(context, 0, gTrigDigitalOutPin, OUTPUT); // writing to TRIGGER pin | |
| 80 | state = LOW; | |
| 81 | digitalWriteOnce(context, n, gTrigDigitalOutPin, state); | |
| 82 | } else if (gTriggerCount == gTriggerInterval+1) { | |
| 83 | pinMode(context, 0, gTrigDigitalOutPin, OUTPUT); // writing to TRIGGER pin | |
| 84 | state = HIGH; | |
| 85 | digitalWriteOnce(context, n, gTrigDigitalOutPin, state); | |
| 86 | } else if (gTriggerCount == gTriggerInterval+2) { | |
| 87 | gTriggerCount = 0; | |
| 88 | state = LOW; | |
| 89 | digitalWriteOnce(context, n, gTrigDigitalOutPin, state); | |
| 90 | } else { | |
| 91 | pinMode(context, 0, gTrigDigitalOutPin, INPUT); // writing to TRIGGER pin | |
| 92 | } | |
| 93 | ||
| 94 | auto dRead = digitalRead(context, n, gEchoDigitalInPin); | |
| 95 | int pulseLength = pulseIn.hasPulsed(context, n); // will return the pulse duration(in samples) if a pulse just ended | |
| 96 | ||
| 97 | float duration = 1e6 * pulseLength / context->digitalSampleRate; // pulse duration in microseconds | |
| 98 | ||
| 99 | static float distance = 0; | |
| 100 | if(pulseLength >= gMinPulseLength){ | |
| 101 | // rescaling according to the datasheet | |
| 102 | distance = duration / gRescale; | |
| 103 | } | |
| 104 | static int count = 0; | |
| 105 | if(count > 5000){ // we do not want to print the value every time we read it | |
| 106 | rt_printf("pulseLength: %d, distance: %fcm\n", pulseLength, distance); | |
| 107 | count = 0; | |
| 108 | } | |
| 109 | ++count; | |
| 110 | // Logging to the scope the pulse inputs (gEchoDigitalInPin) and the distance | |
| 111 | scope.log(dRead * 0.5, distance/100); | |
| 112 | } | |
| 113 | } | |
| 114 | ||
| 115 | void cleanup(BelaContext *context, void *userData) | |
| 116 | { | |
| 117 | } | |
