Unmanned aerial vehicles (UAVs), commonly known as drones, are not new. Fans have been designing and building impressive RC planes, helicopters and even flying inflatable sharks for a long time. The concept of the drone dates back to the mid-19th century, when Austria was sent off without a bomb, and the bomb filled the balloon to attack Venice. Later became the beginning of the development of today's drones in the early 20th century, they were used for the purpose of the practice, the military demand during the First World War has promoted the capabilities of drones, looking for new heights and commercial interests in the effort How can they use drones to train military personnel skills. Currently, Amazon has been trying to use GPS to navigate to your location, enabling automated delivery of drones on the same day. Law enforcement and citizen authorities have also demonstrated how effective drones can be used in tasks such as search and rescue and border patrols. This article looks at some of the options we have when designing control and data link drones. It explores the development and maturity of R/C units, opens up the road, and presents errors when the required safety, anti-interference ability is increased and autonomy is certain.
From toys to tools
We have all had some contact with radio remote control toys, such as small electric cars. A small steering wheel lets your position wheel and a basic throttle let him go. . Polarity switch, which can be reversed. While interesting hobbies and entertainment, even this simple feature has proven to be a useful consumption scouting or surveillance system, prior to military or law enforcement personnel. Initially, radio-controlled cars, helicopters, airplanes, and toys, in most cases, use frequencies of 27 MHz or 49 MHz. The US Federal Communications Commission grants these frequencies to basic consumer goods such as toys, garage door openers, walkie-talkies, and more. The 50 and 53 MHz frequencies are higher if the operator is a licensed amateur radio operator with a larger allowable output power level that can be used. In addition, the 72 MHz and 75 MHz bands can be used for more advanced communication links with additional channels (Table 1). Different countries and regions of the world allow different frequencies and power levels1 and determine which are prohibited. The military can use any power level they want to bring in a crisis situation. The output power of the transmitter, sometimes dictating watts, is more accurately represented by the interoperability determined by the effective radiated power measurement. For example, in the 27 MHz and 49 MHz bands, only one 27 MHz unit can be operated close to another. The same 49 MHz. Crosstalk causes interference per unit.
Table 1: Radio control of common channels and frequencies. The number of channels is also a limiting factor. Normally, 6 channels are used for a simple toy. This is forward, backward, forward, left, front right, back, left, right rear. As you can see, the toys are not very accurate, which is why it takes some developed skills to fly R/C airplanes and helicopters. In addition, radio-controlled toys use time-aligned pulse coding formats (Figure 1). The time slots here are assigned to each channel. If one of the logics is in place, it is active and open. Similarly, if there is no bit at that point in time, it is off. The analog level can be expressed in this way by changing the pulse width. A lack of pulses may be fully off, and a full duty cycle may indicate full open. The level between them corresponds to the duty cycle of the pulse.
Figure 1: Standard Pulse Code Modulation Technique Radio control allows multiple channels to be controlled by the presence or absence of pulses in the time slots associated with the channel. The pulse width can be used to represent the analog level. The higher frequency band does not propagate, as long as the lower frequency signal is used, but there are also channels that are more available using the higher frequency band. This means that interoperability is feasible and a bit reliable when it comes to saying that more than a dozen drones use the 2.4 GHz band due to spread spectrum technology (which also makes compared to narrowband AM and FM higher transmit power) Level). This can help overcome the problem of long distance drone distance. Lower frequencies have better penetration of the surface, however, it may be desirable for lower frequencies than non-air remotes. For example, a camera rover drone can use the building to find criminals and hostages. Interference from walls and compartments, even the 2.4 GHz wireless network array, may make some of the EZRADIO series like Silicon Labs useful. For example, the 315-915 MHz Silicon Labs SI4313-B1-FM or the 240-960 MHz SI4330-B1-FM accessory provides a fairly good data transfer rate of up to 128 kbit/s. Although not high definition, real-time video capabilities; control, telemetry, data acquisition and sensor interfaces are well suited for applying these rates. A good signal sensitivity of -118 dBm means that even weak signals will be available and the designer's modulation techniques can be chosen from them, including FSK, GFSK and OOK modulation options. A particularly good feature is its programmable bandwidth ranging from 2.6 kHz to 620 kHz. This allows designers to choose channel widths and spacing, allowing for more channels (interoperability) and narrower band tasks (such as throttle or steering, which typically occur at low data rates). The low power of 10nA shutdown current is good for inactive periods, and a built-in RSSI can even be sent back to the control point to dynamically adjust the transmit power as needed. Another advantage is that the small (4 mm & TImes; 4 mm) 20-pin components have frequency hopping and mixed signal capabilities, as well as a built-in low battery detector and temperature sensor. Even the smaller 315 MHz-917 MHz Silicon Labs SI4356-B1A-FM is available in a 3mm x 3mm package. Silicon Labs also offers a solar energy harvesting development kit. The energy HARVEST-RD demonstrates how these low-power (12 mA) receiver links can extract enough energy to keep the command channel alive while its independent power supply is charging. .
Miniaturization is the key
These days, anyone can use the commercially available technology (COTS) to make a fairly complex drone. Remote control connections, hobby and industry, have evolved to provide clean performance, remote sensing capabilities, and even streaming video and audio. Modern components make these subsystems small. Ordinary citizens can now have a little spy drone patrolling their house if they choose. Even the pocket drone has been built. Higher frequency radios allow for wider bandwidth. The 2.4 GHz frequency has a 1 MHz wide channel, allowing higher data rates for channels in the 15 kHz range below the 49 MHz band. This allows data or control bursts and allows for audio and video interoperability with live broadcast. Miniaturization is the key to today's drones. Simple low frequency radio control links can be very small and light because they can be implemented using only a few transistors. In contrast, complex spread spectrum radios are based on microcontrollers and carry all the supporting circuits and power requirements of their complex digital radios. Higher frequency operation, however, allows for the use of smaller RF discretes such as inductors, impedance matching components and antennas. The 2.4 GHz band has also become more relevant to most radio remote control enthusiasts, drone manufacturers. Yes, you can buy relatively complex radio-controlled drones, now they use 2.4 GHz radios. This means that a large number of single-chip receivers, transmitters and transceivers can be a fair game when planning their own designs. The 2.4 GHz scheme is easy and can also be band limited. For example, busy wireless network connections such as ZigBee, Bluetooth, and even Bluetooth low-power aspects may limit signal reliability and limit transmit power levels to achieve maximum distance, especially if someone uses active interference. All key data must be acknowledged and the ACK/NACK established protocol ensures that the packet is conditionally licensed for error-free transmission. In addition, the modern 2.4 GHz protocol has a higher bandwidth data rate and an independent control link for allowable audio and video streams. For example, audio and video links from different manufacturers can be streamed concurrently with different channel control and status information. The key point is that the availability of Wi-Fi tablets, smartphones, laptops and laptops can make these bands desirable because a reliable and low-cost control platform is readily available on most smartphones. An application can be your controller. ZigBee's remote control can also be used as a low-cost tester. ZigBee's mesh networking feature also provides a good solution when traffic congestion is a problem. Arbitration, routing, and messaging systems are designed to use other nodes as a starting point to find a route to a particular destination. A good solution here is the Atmel AT86RF231夙, a small 32-pin dedicated transceiver designed for 700, 800, 900 MHz and 2.4 GHz designs. Atmel's ATREB231FE2-EK reference design is a good start. Keep in mind that, as always, RF PCB layout can be tricky.
This is very good for the king
Although government agencies and military groups use large powers in any frequency band they want, because they want and use spread-spectrum technology to quietly coexist, unlicensed industries and people do not have the same abilities of luxury. Instead, we are limited to the R/C band and the ISM band. Others can use it with permission. When it announced that 30,000 drones were in use on the continental United States, and despite the surprise of many, we can expect this number to grow rapidly, especially with law enforcement (Figure 2).
Figure 2: Civil authorities, especially law enforcement agencies, border patrols, and DEA have been using drones in the continental United States for a long time now. For serious missions, satellites still offer a large area of ​​targeted coverage when insured. With expensive operation, a satellite link can be the only way to get the line of sight and get the signal through. Another factor to keep in mind is that autonomy should be programmed to a certain extent. If you lose control for a short time, the drone should enter safe mode. Related to this is the use of the GPS module to let your drone go home, if everything fails. Drones are a fact of life, and the technology can be used. We are entering a personal drone market for legitimate private and commercial use, as well as law enforcement and military use, and will certainly accelerate the first phase. For more information on the components discussed in this article, please provide a link to the product page of the Digi-Key inquiring website.
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