ULTRASONIC RANGE FINDER
An ultrasonic range finder sensor enables a robot to detect obstacles in its path by utilizing the propagation of high-frequency sound waves. The sensor emits a 40 kHz sound wave, which bounces off a reflective surface and returns to the sensor. Then, using the amount of time it takes for the wave to return to the sensor, the distance to the object can be computed. Unlike the bumper switch and limit switch that alert you when they have been hit, the ultrasonic range finder sensor can alert you to an obstacle in the path of the robot prior to hitting it. This can allow you time to safely navigate around obstacles. The sensitivity of the sensor depends on the objects’ surfaces that are detected by the emitted sound waves. For example, a reflective surface may produce a different reading than a non-reflective surface. The resolution of the sensor depends on the sound waves. However, sound waves can reflect or be absorbed and possibly not return with enough power. The sensor can be used to determine distances to objects. It can be used as a tool to determine if any objects are in the robot’s path at all. To increase the sensing range, the sensor can be mounted to a servo to allow it to rotate. Figure 2 below shows a robot that utilizes such a setup.
A line tracker mostly consists of an infrared light sensor and an infrared LED. It functions by illuminating a surface with infrared light; the sensor then picks up the reflected infrared radiation and, based on its intensity, determines the reflectivity of the surface in question. Lightly colored surfaces will reflect more light than dark surfaces; therefore, lightly colored surfaces will appear brighter to the sensor. This allows the sensor to detect a dark line on a pale surface, or a pale line on a dark surface. The line tracker allows your robot to follow a pre-marked path and allows humans to indirectly control the robot while it is autonomous. The line tracker enables a robot to autonomously navigate a line-marked path. By drawing a line in front of a robot outfitted with a line tracker, one can dictate the robot’s patch by showing it where to go without using a remote controller. A typical application uses three line trackers, with the middle sensor aligned directly above the intended line. The range for the line tracker is approximately 0.02 to 0.25in (from the ground) with optimum sensitivity at 3 mm (about 1/8 inch). The minimum line width it can detect is 0.25in. The line tracker is an analog sensor, meaning that it can output many more values within its range of potential values (in this case, from 0-5V) than a digital sensor, which would output only a handful of discrete values in the range (e.g., 1, 2, 3, 4, and 5V), as is the case for a digital sensor. This range of output from 0-5V is sent to the microcontroller, which translates it into a corresponding range of integer values from 0 to full scale. Full scale is 1023 for 10-bit Analog-to-Digital values such as with easyC or ROBOTC for PIC, 4095 for 12-bit values such as with ROBOTC for Cortex and 255 for 8-bit values such as with MPLAB. When using the Cortex Microcontroller, typical white/black/"away from everything values" will be 38/662/770 for easyC, 153/2650/3076 for ROBOTC and 9/166/192 for 8-bit values. When using the PIC Microcontroller, typical white/black/"away from everything values" will be 38/882/1012 for both easyC and ROBOTC and 9/220/253 for 8-bit values For this particular sensor, the output will be low when the surface is pale or highly reflective and high when the surface is dark and absorbs infrared energy.
The bumper switch is a pushbutton that when pressed can cause the robot to respond as programmed. It does this by maintaining a HIGH signal on its sensor port, which means the bumper switch is turned off when not pressed. While the bumper switch is pressed, the signal changes to LOW,...
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