Serial Number Transmit 4.2 Mac
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The ESP32 Bluetooth has 8 transmit power levels, corresponding to -12 ~ 9 dBm of transmit power, with a 3 dBm interval. The controller software limits the transmit power and selects the power level according to the corresponding power level declared by the product.
Currently, ESP32 Bluetooth LE fully supports some basic profiles, such as GATT/SMP/GAP, as well as some self-defined profiles. The ones that have already been implemented include Bluetooth LE HID (receiving side), Bluetooth LE SPP-Like, Battery, DIS, BluFi (Bluetooth Network Configuration-transmitting side), and so on.
In an open environment, the transmission rate for ESP32 Classic Bluetooth SPP can reach 1400+ Kbps ~ 1590 Kbps (only for reference, please do tests based on your actual application environment) with bi-directional transmitting and receiving simultaneously.
The power level of ESP32 Bluetooth ranges from 0 to 7, with the corresponding transmit power ranges from -12 dBm to 9 dBm. Each time the power level increases by 1, the corresponding transmit power will increase by 3 dBm.
There is no exact number for maximum Bluetooth LE connections. When there are multiple devices connected to Bluetooth LE simultaneously, the RF is time-multiplexed, thus requiring the designer to ensure that each device is not overly occupied, causing other devices to timeout and disconnected.
The transmission is slow When a large number of data packets on the Bluetooth channel are transmitted for multi-packet reading. You can improve the transmission speed by adjusting the Bluetooth connection parameters.
ESP32 Classic Bluetooth has two protocols, namely A2DP and SPP. The maximum MTU Size setting of BT A2DP (default) is 1008 bytes, of which the header occupies 12 bytes and the actual amount of data transmitted by the application layer is 1008 - 12 = 996 (bytes); the maximum MTU Size of BT SPP (default) Set to 990 bytes.
Chapter 1 described how to connect the Arduino serial port to your computer to upload sketches. The upload process sends data from your computer to Arduino and Arduino sends status messages back to the computer to confirm the transfer is working. The recipes here show how you can use this communication link to send and receive any information between Arduino and your computer or another serial device.
Your Arduino sketch can use the serial port to indirectly access (usually via a proxy program written in a language like Processing) all the resources (memory, screen, keyboard, mouse, network connectivity, etc.) that your computer has. Your computer can also use the serial link to interact with sensors or other devices connected to Arduino.
Implementing serial communications involves hardware and software. The hardware provides the electrical signaling between Arduino and the device it is talking to. The software uses the hardware to send bytes or bits that the connected hardware understands. The Arduino serial libraries insulate you from most of the hardware complexity, but it is helpful for you to understand the basics, especially if you need to troubleshoot any difficulties with serial communications in your projects.
Boards including the Uno, Duemilanove, Diecimila, Nano, and Mega have a chip to convert the hardware serial port on the Arduino chip to Universal Serial Bus (USB) for connection to the hardware serial port. Other boards, such as the Mini, Pro, Pro Mini, Boarduino, Sanguino, and Modern Device Bare Bones Board, do not have USB support and require an adapter for connecting to your computer that converts TTL to USB. See for more details on these boards.
Some serial devices use the RS-232 standard for serial connection. These usually have a nine-pin connector, and an adapter is required to use them with the Arduino. RS-232 is an old and venerated communications protocol that uses voltage levels not compatible with Arduino digital pins.
The Arduino Mega has four hardware serial ports that can communicate with up to four different serial devices. Only one of these has a USB adapter built in (you could wire a USB-TTL adapter to any of the other serial ports). Table 4-1 shows the port names and pins used for all of the Mega serial ports.
You will usually use the built-in Arduino serial library to communicate with the hardware serial ports. Serial libraries simplify the use of the serial ports by insulating you from hardware complexities.
Sometimes you need more serial ports than the number of hardware serial ports available. If this is the case, you can use an additional library that uses software to emulate serial hardware. Recipes 4.13 and 4.14 show how to use a software serial library to communicate with multiple devices.
The hardware or software serial libraries handle sending and receiving information. This information often consists of groups of variables that need to be sent together. For the information to be interpreted correctly, the receiving side needs to recognize where each message begins and ends. Meaningful serial communication, or any kind of machine-to-machine communication, can only be achieved if the sending and receiving sides fully agree how information is organized in the message. The formal organization of information in a message and the range of appropriate responses to requests is called a communications protocol.
To display text and numbers from your sketch on a PC or Mac via a serial link, put the Serial.begin(9600) statement in setup(), and then use Serial.print() statements to print the text and values you want to see.
The Arduino Serial Monitor function can display serial data sent from Arduino. To start the Serial Monitor, click the Serial Monitor toolbar icon as shown in Figure 4-2. A new window will open for displaying output from Arduino.
Your sketch must call the Serial.begin() function before it can use serial input or output. The function takes a single parameter: the desired communication speed. You must use the same speed for the sending side and the receiving side, or you will see gobbledygook (or nothing at all) on the screen. This example and most of the others in this book use a speed of 9,600 baud (baud is a measure of the number of bits transmitted per second). The 9,600 baud rate is approximately 1,000 characters per second. You can send at lower or higher rates (the range is 300 to 115,200), but make sure both sides use the same speed. The Serial Monitor sets the speed using the baud rate drop down (at the bottom right of the Serial Monitor window in Figure 4-2). If your output looks something like this:
The values (numbers) that you print depend on the type of variable; see Recipe 4.2 for more about this. But for now, printing an integer will print its numeric value, so if the variable number is 1, the following code:
In the example sketch, the number printed will be 0 when the loop starts and will increase by one each time through the loop. The ln at the end of println causes the next print statement to start on a new line.
You can use a liquid crystal display as a serial output device, although it will be very limited in functionality. Check the documentation to see how your display handles carriage returns, as some displays may not automatically advance to a new line after println statements.
Receiving numbers with more than one digit involves accumulating characters until a character that is not a valid digit is detected. The following code uses the same setup() and blink() functions as those shown earlier, but it gets digits until the newline character is received. It uses the accumulated value to set the blink rate.
Each digit is converted from its ASCII value to its numeric value. Because the numbers are decimal numbers (base 10), each successive number is multiplied by 10. For example, the value of the number 234 is 2 * 100 + 3 * 10 + 4. The code to accomplish that is:
Another approach to converting text strings representing numbers is to use the C language conversion function called atoi (for int variables) or atol (for long variables). These obscurely named functions convert a string into integers or long integers. To use them you have to receive and store the entire string in a character array before you can call the conversion function.
Another approach is to use a library called TextFinder, which is available from the Arduino Playground. TextFinder was created to extract information from web streams (see Chapter 15), but it works just as well with serial data. The following sketch uses TextFinder to provide similar functionality to the previous sketch:
Returns the first valid (long) integer value. Leading characters that are not digits or a minus sign are skipped. The integer is terminated by the first nondigit character following the number. If no digits are found, the function returns 0.
Same as getValue, but the given skipChar within the numeric value is ignored. This can be helpful when parsing a single numeric value that uses a comma between blocks of digits in large numbers, but bear in mind that text values formatted with commas cannot be parsed as a comma-separated string.
Finds the pre_string and then puts the incoming characters into the given buffer until the post_string is detected. The end of the string is determined by a match of a character to the first char post_string. Strings longer than the given length are truncated to fit. The function returns the number of characters placed in the buffer (0 means no valid data was found).
You can also send binary data using structures. Structures are a mechanism for organizing data, and if you are not already familiar with their use you may be better off sticking with the solutions described earlier. For those who are comfortable with the concept of structure pointers, the following is a function that will send the bytes within a structure to the serial port as binary data:
The draw function in Processing works like loop in Arduino; it is called repeatedly. The code in draw checks if data is available on the serial port; if so, bytes are read and converted to the integer value represented by the bytes. A rectangle is drawn based on the integer values received. 2b1af7f3a8