Ultrasonic sensor is a sensor that works on the principle of reflection of sound waves and is used to detect the presence of a particular object in front of it, it works on the area above the frequency of sound waves from 40 KHz to 400 KHz. Ultrasonic sensors(also known astransceiverswhen they both send and receive) work on a principle similar toradarorsonar whichevaluate attributes of a target by interpreting the echoes from radio or sound waves respectively. Ultrasonic sensors generate high frequency sound waves and evaluate the echo which is received back by the sensor. Sensors calculate the time interval between sending the signal and receiving the echo to determine the distance to an object.
Ultrasonic Sensor working principle
Ultrasonic sensor consists of two units, namely the transmitter unit and receiver unit. Transmitter and receiver unit structure is simple, a piezoelectric crystal is connected with mechanical anchors and only connected with the diaphragm vibrator. Alternating voltage with a frequency of 40 kHz – 400 kHz are given on the metal plate. The atomic structure of the piezoelectric crystal will contract (binding), expanded or shrunk to the polarity of applied voltage, and is called the piezoelectric effect. Contractions that occur forwarded to the diaphragm resulting in an ultrasonic vibrator emitted into the air (the surroundings), and the reflection of ultrasonic waves will occur when there is a particular object, and the reflection of ultrasonic waves to be received back by the receiver sensor units. Furthermore, the sensor unit will cause the diaphragm vibrator receiver will vibrate and the piezoelectric effect produces an alternating voltage with the same frequency.
Large amplitude signals generated elekrik receiver sensor units depends on the distant object detected nearby and the quality of the sensor transmitter and receiver sensors. Yuang sensing process performed on this sensor using the reflection method to calculate the distance between the sensor with the target object. The distance between the sensors is calculated by multiplying half the time used by the ultrasonic signal in the way of a series of Tx to Rx is received by the circuit, with the speed of propagation of ultrasonic signal propagation on the use of media, namely air.
Time in the count when pemencar active and until there is input from the receiver circuit and when at a certain time limit circuit receiving no input signal is considered to be no obstacle in front.
IR Sensor circuit is one of the most basic and popular sensor modules. In electronics, this sensor is analogous to human’s visionary senses which can be used to detect an obstacle which is one of its common applications. In robotics, a group of such modules are used so that a robot can follow a line pattern.
As you begin to delve deeper into the abstruse domain of sensors and varying methodology adopted for implementing intelligence in your robot, IR sensors would definitely be one of the most easy to operate upon, simple yet instrumental tool in your arsenal. This forms one of the most important topics of our robotic workshops, training and tutorials.
Infra red sensors are the most often used sensor by amateur roboteers. Understanding how they behave can help address many of your requirements and would suffice to address most of the problem statements for various robotics events. Be it a typical white/black line follower, a wall follower, obstacle avoidance, micro mouse, an advanced flavor of line follower like red line follower, etc, all of these problem statements can be easily addressed and granular control can be exercised upon your robots performance if you have a good operational understanding of Infra red sensors.
Infra red sensors are in the form of diodes with 2 terminals. You can buy a pair of such diode (one transmitter and one receiver) at a very low cost of about 5 - 7 rupees only. Here onwards, we will use Tx to refer to a transmitter and Rx to refer to a receiver diode.
Operation:
When the Tx is forward biased, it begins emitting infra red. Since it’s not in visible spectrum, you will not be able to see it through nakedeyes but you will be able to view it through an ordinary cell phone camera.
The resistance R1 in the above circuit can vary. It should not be a very high value (~ 1Kohm) as then the current flowing through the diode would be very less and hence the intensity of emitted IR would be lesser. By increasing the current flowing in the circuit, you can increase the effective distance of your IR sensor. However, there are drawbacks of reducing the resistance. Firstly, it would increase the current consumption of your circuit and hence drain the battery (one of the few ‘precious’ resources for any embedded system) faster. Secondly, increasing the current might destroy the Tx. So, the final choice should be a calculated trade off between these various factors.
Fig: Typical Transmitter Circuit
You can also modulate the IR to achieve better distance and immunity.The receiver diode has a very high resistance, typically of the order of mega Ohms when IR is not incident upon it. However, when IR is incident upon it, the resistance decreases sharply to the order of a few kilo Ohms or even lesser. This feature forms the basis of using IR as a sensor. You will need to connect a resistance of the order of a few mega Ohm in series with the Rx. Then tap the output voltage at the point of connectivity of these two resistors. A complete Tx-Rx circuit is given below.
Fig: Transmitter Receiver Pair Circuit
Remember, the value of R2 can vary depending upon the Rx diode you are working with. You are advised to first check the resistance of Rx diode with no IR incident upon it and then select the value of R2 for decent performance.
Case1: when no IR is incident upon the Rx
Rx would be of the order of mega ohms and hence the output voltage would be around 2.6v – 3v depending upon your choice of R2 and the Rx.
Case2: when IR is incident upon the Rx
The resistance of Rx will sharply fall and hence the output voltage would be around 1.8v - 1.5v depending upon your choice of Rx and R2.
Once you obtain a neat difference between the output voltages in case1 and case2, your sensor is ready.
Ultrasonic sensors are relatively simple and easy to interface with and thus are a good sensor to use in robotics. The sensor emits a sonic pulse and then waits for the returned echo reflecting off an object. The pulse is emitted by a transducer which converts between electrical, mechanical, and sonic energy(Ultrasonic FAQ). The time between the sent pulse and the returned echo is used to calculate distance. Ultrasonic sensors are not perfect and do have drawbacks. The emitted pulse has a cone shape and any object the pulse encounters will return an echo(lynxmotion.com). It is not possible to discern between small objects, such as a broomstick, and large objects such as a chair or wall for this reason as both will return an echo(Shinsel). These drawbacks can be overcome by using multiple or rotating sensors(Shinsel). How do ultrasonic sensors work?
Figure 1
Ultrasonic sensors are a simple device. They send out an ultrasonic pulse and then wait for a response. When the pulse leaves the device, it travels through the air until it collides with an object, at which point an echo is reflected back. This echo is then sensed by the ultrasonic sensor. The sent pulse is anywhere from 40-200khz, but is typically in the 40-50khz range(Ultrasonic FAQ).
Transducer The piece of hardware that sends the original pulse and senses the returned echo is a called a transducer. There are two types of transducers: electrostatic and piezo. Electrostatic Transducers(Ultrasonic FAQ) Electrostatic transducers are similar to a capacitor. They consist of a fixed plate and a moveable plate. The fixed plate is usually aluminum and the moveable one is Kapton[1] coated with a thin gold layer. The Kapton acts as an insulator. When a signal is applied to the two plates (typically at 50hz), the gold foil is attracted to the backplate which displaces air and creates an ultrasonic burst. Piezo Transducers(Ultrasonic FAQ) Piezo electric transducers use the peizo effect[2] to create and measure ultrasonic pulses. The sensors use a crystal or ceramic material bonded to a metal case or cone. To emit the pulse, the crystal is excited by a signal (usually 40khz), which expands or contracts the piezo material. The connected metal cone also expands or contracts which generates the ultrasonic burst. The return echo causes the piezo material to vibrate, which generates a signal. Piezo transducers are generally less expensive than electrostatic transducers, but their construction makes them better suited for harsh environments. Distance Calculation The distance calculation is quite simple. Once the pulse is sent and the echo is sensed, one only needs to use the following equation to find the distance(Ohya): The maximum distance that can be sensed varies with the power and sensitivity of the transducer. The inexpensive sensors used in robotics typically sense up to 3m(lynxmotion.com), while high quality ultrasonic sensors can sense in upwards of 10m(Polariod). Interface
Figure 2
Most ultrasonic sensors used in robotics come in a module that includes the control circuitry. Usually the only signals required are an INIT and ECHO signal(lynxmotion.com). The use of these signals is illustrated using the spec sheet for the Devantec ultrasonic sensor(lynxmotion.com).
To trigger the sensor, send a 10us pulse to the INIT line. After the INIT line falls low, the sensor will emit a sonic burst. After the sonic burst is emitted, the ECHO line will go high and will remain high until the sensor receives an echo. It will time out after 36ms, which means it did not receive an echo, i.e., no object was detected. The limitations of ultrasonic sensors
Figure 3
Figure 4
The majority of the limitations of ultrasonic sensors are directly related to the cone shape of the emitted pulse(Ohya). One of the major problems is that anything in the sensors path will return a pulse. There is no way to discern between a 1in pipe and a wall, because both will return an echo. This problem can be fixed by using multiple sensors or by rotating a single sensor(Shinsel). If the multiple sensor solution is used, you can either place the sensors at the same point and angle them, as in figure 3, or place them apart, as in figure 4. In either case, if an object is sensed by both sensors, you have a better idea of where the object lies. The angle idea is expanded in the rotating solution. A single sensor is rotated, and readings are taken at certain intervals. This method gives an even better idea about the location of objects. Another problem with ultrasonic sensors is that it can be hard to sense openings in a wall such as a door or corner(Shinsel). If one side of the opening falls into the sonic cone, it will return an echo. Therefore, to sense openings it is best for the sensor to be close to the opening or to have a narrowed sonic cone. A narrowed cone can be accomplished by using a horn. A horn attaches to the end of the transducer and directs the ultrasonic pulse into a narrower cone. There are limitations to using horns. Since the sonic cone is narrower, less objects are sensed at a close proximity. Using a combination of sensors is usually a good idea.
A week ago, amateur astronomers were marveling over a curious cloud that they spotted on the Mars — and now the professionals are focusing in on an explanation.
The cloud was intriguing because it was most noticeable along the very edge of the Martian disk, and seemed to project high into the atmosphere. Some suspected that it might be a cloud of dust thrown up by an impact on the Red Planet. So, over the past week, professionals and amateurs have been working together to collect imagery and analyze the hazy spot.
"It's most likely a condensate cloud/haze, H2O in composition," Bruce Cantor, senior staff scientist at Malin Space Science Systems, said in an email that was circulated to other experts. "Similar type of phenomena have been seen in early-morning orbital observations in the past."
Amateur astronomer Wayne Jaeschke, who first observed this month's Martian cloud, appreciated getting the word.
"That's very interesting, as my first report on the subject suggested that it was a high-altitude water-ice cloud," Jaeschke told me in an email. "I wouldn't be surprised if that's what the consensus turns out to be."
Checking scenarios Jaeschke said that he's been in contact with other astronomers who are looking at data from the Mars Color Imager, or MARCI, which is one of the instruments on NASA's Mars Reconnaissance Orbiter. "To date, the data shows that there was no abnormal dust activity at Mars' southern latitudes, further reducing the possibility that this was some sort of high-altitude dust storm, impact strike, or other similar phenomena," he said.
The fact that MARCI saw no abnormal cloud activity during its passes at 3 a.m. and 3 p.m. local Mars standard time suggests that the mystery cloud was a transient feature — for example, morning clouds that dissipated by the afternoon on Mars. "Still, researchers are suspect of normal cloud activity, due to the large size of the phenomenon and apparent altitude," Jaeschke said.
One of the more exotic scenarios suggests that the morning clouds were lit up by localized auroral activity, sparked by a recent string of solar storms. "Mars doesn't have a magnetic field similar to that on Earth, but Mars Global Surveyor mapped 'umbrella-like' localized fields back in 2004," Jaeschke said.
THEMIS on the case The High Resolution Imaging Science Experiment, or HiRISE, the powerful camera on Mars Reconnaissance Orbiter, is designed to take up-close looks at the Martian surface, but not the atmosphere. So HiRISE is unlikely to shed any additional light on the cloud question. But the team for the Mars Odyssey orbiter's Thermal Emission Imaging System, or THEMIS, has been trying to get pictures of the cloud, as well as the clouds hanging around Mars' big shield volcanoes.
"Of the nine images we targeted over the region with that large cloud, only four have been downlinked so far," Jonathon Hill, a member of the THEMIS mission operations team, told me in an email on Wednesday. "And unfortunately, it looks like the cloud either moved or is so think that we can't really see it when we're zoomed in that close."
Today, Hill provided another email update:
"We've downlinked a couple more of the images we targeted over the region with the large high-altitude clouds, but unfortunately they're all very clear without any sign of cloud activity.
"I'm starting to suspect that the clouds people have been photographing are just so wispy and thin that when we look at them zoomed in at about 100 meters per pixel, there's just not enough cloud structure for us to make out. But it is a cool example of how, even though we have a camera in orbit, we have a very limited perspective, which is why we need to combine data from multiple instruments, including ground-based observations, to study the planet as a whole.
"Next week we have some passes over the large Tharsis volcanoes, so we're planning images of their summits, where there's usually a lot of cloud activity this time of year. The good thing about those clouds is that they are anchored by the summits, so we know exactly where they'll be. Hopefully we'll be able to see some structure in them.
"I'll definitely keep you updated. Our atmospheric scientists can't wait to get some good visible/infrared images of these late spring clouds!"
Bottom line? The likeliest explanation for the mystery cloud seems to be the one Cantor came up with: It's a seldom-seen but far from unprecedented manifestation of Martian morning weather. For more of the expert amateur opinion, check out the Unmanned Spaceflight website, the Cloudy Nightsonline forum and the Mars Observers group on Yahoo.
Jaeschke's picture of Mars, featuring the cloud cover surrounding the Red Planet's monster volcanoes, served as this week's "Where in the Cosmos" picture puzzle on the Cosmic Log Facebook page. It didn't take long for my Facebook friends to figure out what the picture showed, and even name the four big volcanoes (Olympus Mons, Ascraeus Mons, Pavonis Mons and Arsia Mons). For solving this week's mystery so quickly, Rick Casey and Shelton Howard will be getting some 3-D glasses in the mail, plus a 3-D picture of yours truly. Keep your eyes peeled for next week's "Where in the Cosmos" puzzle on Facebook.
The Martian mystery cloud was one of the subjects discussed during this week's Space Hangout, hosted by Pamela Gay with Emily Lakdawalla, Ian O'Neill and yours truly as comme
