In the autonomous walking robot system, in order to realize walking in an unknown and uncertain environment, the robot must collect environmental information in real time to achieve obstacle avoidance and navigation. This must be realized by a sensor system that can realize the sensing environment information. Sensors such as vision, infrared, laser, and ultrasonic are widely used in walking robots. The ultrasonic ranging method has been widely used because of its simple equipment, low price, small size, simple design, easy real-time control, and industrial and practical requirements in terms of measuring distance and measurement accuracy. The robot described in this paper uses a three-way ultrasonic ranging system that provides information about the distance of motion for the robot to identify the front, left and right environments of its motion.
Ultrasonic ranging principle
The inside of the ultrasonic generator consists of two piezoelectric sheets and a resonance plate. When a pulse signal is applied to its two poles and its frequency is equal to the natural oscillation frequency of the piezoelectric wafer, the piezoelectric wafer will resonate and drive the resonance plate to vibrate to generate ultrasonic waves. On the other hand, if no external voltage is applied between the two poles, when the resonator plate receives the ultrasonic wave, it becomes an ultrasonic receiver. There are generally two methods for ultrasonic ranging: 1 taking the average voltage value of the output pulse, which is proportional to the distance, and measuring the voltage to measure the distance; 2 measuring the width of the output pulse, that is, the time interval t between transmitting the ultrasonic wave and receiving the ultrasonic wave, According to the measured distance s=vt? 2 to get the measurement distance, because the ultrasonic velocity v is related to temperature, if the temperature change is relatively large, it should be corrected by the temperature compensation method.
The second method is adopted in the measurement system. Since the measurement accuracy requirement is not particularly high, the temperature can be considered to be substantially unchanged. The system uses PIC16F877 microcontroller as the core, realizes real-time control of peripheral circuits through software programming, and provides signals required for peripheral circuits, including frequency vibration signals and data processing signals, thus simplifying peripheral circuits and good portability. . The block diagram of the system hardware is shown in Figure 1.
Figure 1 system hardware circuit block diagram
Since the system only needs to know whether there are obstacles in front, left or right of the robot, and does not need to know the specific distance between the obstacle and the robot, there is no need to display the circuit, only need to set a distance threshold to make the obstacle and When the distance of the robot reaches a certain value, the MCU controls the robot motor to stop, which can be realized by software programming.
Ultrasonic transmitting circuit
The ultrasonic transmitting circuit takes PIC16F877 as the core. When the MCU is powered on, the MCU generates a 40 kHz ultrasonic signal from the RA0 port. However, at this time, the signal cannot pass through the NAND gate to enter the amplifying circuit to cause the ultrasonic transmitting head to emit ultrasonic waves. Only when the switch S1 is closed, A gate signal is transmitted from the RA1 port. The frequency of the signal is 4 kHz. At the same time, the timer TMR1 inside the microcontroller is started to start counting. Each time the gating signal is transmitted, the ultrasonic wave transmits 10 complete waveforms, which can be derived from their frequencies. The period of the ultrasonic wave is 1 (40 kHz) = 0.1025 ms, and the period of the gating signal is 1 (4 kHz) = 0125 ms. Finally, the distance between the obstacle and the mobile robot is obtained from s=vt2. When the ultrasonic receiving head receives the reflected ultrasonic wave, the counter stops counting, and the time t can be obtained according to the counter counting and the period of the gating signal. The RA2 port is connected to the RS trigger, and the RS trigger can automatically control the emission and stop of the ultrasonic wave. The circuit of the system also includes a manual reset circuit, which is controlled by the MCLR pin of the single chip connected to S2, and the ultrasonic transmitting circuit diagram is shown in FIG.
Figure 2 Ultrasonic transmitting circuit diagram
Gating circuit (RS trigger)
In order to realize automatic control of ultrasonic transmission and reception, a gate control circuit must be added to the circuit. The frequency of the gate signal is 4 kHz. If the output pulse is used as a gate signal, the pulse of the known frequency fc passes through the gate, then t = NTc, where Tc is the period of the known pulse and N is the number of pulses. The gate control circuit is composed of RS flip-flops, which is reset when the input terminal R=1 (S=0), that is, the output terminal Q=0; when R=0 (S=1), it is set, that is, Q=1. The RS flip-flop is connected to the RA2 port of the microcontroller.
Ultrasonic amplifying circuit
The ultrasonic amplifying circuit is composed of a triode or the like. Since the single-chip RA port has a maximum current of 20 mA to 25 mA, and the ultrasonic transmitter requires a minimum current of 60 mA, a first-stage amplification circuit is added after the NAND gate to amplify the current to complete the ultrasonic wave. emission. The ultrasonic amplifying transmitting circuit is shown in Fig. 3.
Figure 3 Ultrasonic amplification transmission circuit diagram
Screen Resolution
There are generally three screen resolutions for office projectors:
One is a 4:3 screen suitable for office PPT playback. The first is the SVGA machine with the lowest price and the highest cost performance. This kind of machine is generally priced at around 2500 and has powerful performance. The disadvantage is that the resolution is 800X600, which is relatively low. The second is the XGA machine, which is an upgraded version of the SVGA machine with a resolution of 1024X768.
The other is the 16:10 aspect ratio screen used by some foreign-funded enterprises, which is the 1280X800 resolution of WXGA. However, with the transparent price of 1080p projectors, more and more companies will choose full HD 1080p projectors as their office projection solutions.
Office Projector Features
According to the needs of different office environments, office projectors are roughly divided into three categories.
One is a conventional projector that is placed or hoisted in the conference room, the second is a Portable Projector that can be carried around, and the third is an ultra-short-throw projector that is convenient for work reports and speeches.
Wireless Office Projector
With the advent of the Internet era, the emergence of a series of wireless office series has added new members to the office projectors. The wireless office projector is realized by the built-in wireless module of the ordinary office projector. Wireless office makes people do not need to switch signal lines frequently in office meetings, allowing people to have a better experience in meetings!
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