An infrared distance Sensor scheme based on 410C Dragonboard
Published in20:18 2016-01-25|
First, the foreword
Infrared distance sensors commonly used in robots, unmanned aerial vehicles and other intelligent hardware equipment, in order to achieve intelligent obstacle avoidance, and can be realized from the measurements of the infrared sensor is less, today is about two kinds of sensor, sensing distance and distance measurement.
Usually the use of infrared distance sensors to achieve the object is close to the distance threshold detection, is a dual state output, that is, outside the range of detection can not be triggered, into the detection range has been in a state of trigger. Another kind of infrared sensor in addition to the former function can be realized, but also the distance between measurement and external objects, so in the measuring range is sustainable output distance data, the motion state of the object tracking to do further processing, to achieve some useful features. Now these two kinds of Sensor are introduced respectively.
Three, Sensor introduction
3.1 near distance sensing (Sensor Proximity)
General range induction Sensor is usually contains an infrared reflection diode and infrared receiving photodiode, which is mostly used in the mobile phone products, to make the call out of the screen to save energy. Now most of the manufacturers have integrated light receiving photodiode for ambient light application, ignore this feature here. Also some manufacturers in order to increase the induction distance, emitting diode do external, using a larger emission power diode, as shown in the following picture, we used here is that, because the induction distance further later. Explain why. In principle, emitting diode emits infrared light of a particular frequency, which is reflected by the external object by the corresponding frequency receiving diode received and changed into electrical strength, by the ADC turn into digital signal, when the signal strength exceeds the trigger threshold (through the I2C setting the trigger threshold), which triggers terminal, said to be close to the external objects. In the design, in order not to make the emitted light directly from the receiving end without the external reflection, the transmitting tube and the receiving tube structure need to be separated from the light source.
3.2 distance measurement (Measuring Sensor Distance)
A. triangle method
Trigonometry measurement principle, as shown in the following picture, the framework with the above sensor similar, also contains specific frequency of infrared emission and receiving unit, the difference is receiving unit is not a simple photodiode, is a PSD (position sensitive detector). Emitting diodes that emit specific frequency infrared light, which is reflected by the external object, received by PSD, emission diode, the outside of the object distance and reflected light in the placement position of the PSD is formed a triangle and PSD can be received on the receiving surface of the infrared point position turn into two current I1 and I2, and distance of the two currents have a certain linear relationship, after ADC can be through a certain algorithm will distance demodulation. Typical application of this method is Sharp.
B.TOF (of Flight Time) method
TOF is a method to calculate the distance by measuring the time difference between the light from the transmitter to the receiver. As shown in the following picture, the structure also with above two kinds of sensor is similar, the same infrared emission and receiving diode, the difference is emitting diode is a particular frequency pulsed infrared light, transmitting and receiving diodes respectively by transmitting and receiving a driving control circuit and driving circuit respectively and sensor built-in timer is connected, transmit or receive a pulsed in a timely manner to trigger the timer, the flight time is by the timer meter emission statistical trigger time and receives the triggering instants of time difference, the time can be directly converted into a distance d = (Vc*T)) / 2.
Four, the experimental program
We can take the Sensor described above to do some small experiments, distance measurement of the two kinds of sensor can measure distance, similar to the macro experience, we can use one of the representative. We envision a car, to DragonBoard410C do control the core, with two step drive four wheels (one for driving after rotation drive, on the other a for controlling the direction of the front wheel), take four proximity sensor are respectively arranged around the car, a distance measuring sensor installed in the front of the car, respectively, to run the two procedures, experience the function of the two sensor. Schematic as follows:
Here, proximity sensor only to obstacle avoidance function, when the car near the obstacles in the process, the sensor will send interrupt trigger signal, APQ8016 receives the interrupt signal will jump to the corresponding interrupt service routine to make corresponding responses, such as the left sensor meets the obstacle, the front wheel motor is the right front wheel, so as to avoid the obstacle of function.
For the distance measuring sensor, when it detects obstacles in front, the first notice the CPU, as diminishing distance, vehicle speed is reduced gradually, setting a safe distance (10cm), when the car close to the obstacle enters into the safe distance range is immediately shut down small motor car, allowing the car to stop, in combination with other sensor combined with corresponding algorithm can realize storage smart car. We can also further design, setting a distance range (such as 50cm-100cm), make the distance between the car and the obstacle has been maintained in the range, then you can realize the car to follow the object function. By contrast, it is easy to find that Sensor Proximity is not the two function.
.More details of the development of Qualcomm please see:Qualcomm developer community.
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