vb.net barcode reader from image FIGURE 30-14 Ultrasonic sensors mounted on an RC servo scanner turret. in Software

Maker QR Code ISO/IEC18004 in Software FIGURE 30-14 Ultrasonic sensors mounted on an RC servo scanner turret.

FIGURE 30-14 Ultrasonic sensors mounted on an RC servo scanner turret.
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FIGURE 30-15 Schematic diagram for a basic ultrasonic proximity transmitter.
The closer the ultrasonic sensor is to an object, the stronger the reflected sound will be. (Note, too, that the strength of the reflected signal will also vary depending on the material bouncing the sound.) The output of the comparator will change between LOW and HIGH as the sensor is moved closer to or farther away from an object. Once you get the circuit debugged and working, adjust potentiometer R2, on the op amp, to vary the sensitivity of the circuit. You will find that, depending on the quality of the transducers you use, the range of this sensor is quite large. When the gain of the op amp is turned all the way up, the range may be as much as 6 to 8 ft. (The op amp may ring, or
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Ultrasonic Transducer
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FIGURE 30-16 Schematic diagram for a basic ultrasonic proximity sensor receiver.
30.3 CONTACT DETECTION
oscillate, at very high gain levels, so use your logic probe to choose a sensitivity setting just below the ringing threshold.)
30.3 Contact Detection
A sure way to detect objects is to make physical contact with them. Contact is perhaps the most common form of object detection and is often accomplished by using simple switches. This section will review several contact methods, including soft-contact techniques where the robot can detect contact with an object using just a slight touch.
30.3.1 PHYSICAL CONTACT BUMPER SWITCH
An ordinary switch can be used to detect physical contact with an object. So-called bumper switches are spring-loaded push-button switches mounted on the frame of the robot, as shown in Fig. 30-17. The plunger of the switch is pushed in whenever the robot collides with an object. Obviously, the plunger must extend farther than all other parts of the robot. You may need to mount the switch on a bracket to extend its reach. The surface area of most push-button switches tends to be very small. You can enlarge the contact area by attaching a metal or plastic plate or a length of wire to the switch plunger. A piece of rigid 1 16-in-thick plastic or aluminum is a good choice for bumper plates. Glue the plate onto the plunger. Low-cost push-button switches are not known for their sensitivity. The robot may have to crash into an object with a fair amount of force before the switch makes positive contact, and for most applications that s obviously not desirable. Leaf switches require only a small touch before they trigger. The plunger in a leaf switch (often referred to as a Microswitch), is extra small and travels only a few fractions of an inch before its contacts close. A metal strip, or leaf attached to the strip, acts as a lever, further increasing sensitivity. You can mount a plastic or metal plate to the end of the leaf to increase surface area. If the leaf is wide enough, you can use miniature 4/40 or 3/38 hardware to mount the plate in place.
Plunger Switch
Frame
FIGURE 30-17 An SPST spring-loaded plunger switch mounted in the frame or body of the robot, used as a contact sensor.
OBJECT DETECTION
30.3.2 WHISKER
Many animal experts believe that a cat s whiskers are used to measure space. If the whiskers touch when a cat is trying to get through a hole, it knows there is not enough space for its body. We can apply a similar technique to our robot designs whether or not a cat actually uses whiskers for this purpose. You can use thin 20- to 25-gauge piano or stove wire for the whiskers of the robot. Attach the wires to the end of switches, or mount them in a receptacle so the wire is supported by a small rubber grommet. By bending the whiskers, you can extend their usefulness and application. The commercially made robot shown in Fig. 30-18, the Movit WAO, has two whiskers that can be rotated in their switch sockets. When the whiskers are positioned so the loop is vertical, they can detect changes in topography to watch for such things as the edge of a table, the corner of a rug, and so forth. A more complex whisker setup is shown in Fig. 30-19. Two different lengths of whiskers are used for the two sides of the robots. The longer-length whiskers represent a space a few inches wider than the robot. If these whiskers are actuated by rubbing against an object but the short whiskers are not, then the robot understands that the pathway is clear to travel but space is tight.
FIGURE 30-18 The Movit WAO robot (one of the older models, but the newer ones are similar). Its two tentacles, or whiskers, allow it to navigate a space.
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