How to Encode Measurements into Bytes with JavaScript

In many IoT (Internet of Things) and embedded systems applications, it's essential to encode sensor measurements or other data into byte arrays before transmitting them over networks. This process often involves converting numerical values into a format that can be efficiently sent over communication protocols that accept binary or byte data. This article demonstrates how to encode measurements into bytes using JavaScript, focusing on a specific case where an integer larger than 255 needs to be split into two bytes.

Encoding Function

Our primary tool for encoding measurements in a Downlink is the Encoder function. This function takes two parameters: measurements, which is the numerical value you wish to encode, and port, which can be used to specify different encoding behaviors based on the application's requirements.

The Encoder Function

function Encoder(measurements, port) {
    // Assuming 'measurements' is the integer we want to split,
    // and it's larger than 255 but fits within a 16-bit range (0 to 65535).
    var integer = measurements; // For clarity, assuming 'measurements' is a single integer.
    
    var lowerByte = integer & 0xFF; // Extract lower 8 bits
    var higherByte = (integer >> 8) & 0xFF; // Shift right 8 bits and extract lower 8 bits
    
    // The function returns an array of bytes. 
    // Adjusted order to [lowerByte, higherByte] if that matches your expected byte order (Little Endian).
    // For Big Endian (most significant byte first), use [higherByte, lowerByte].
    return [higherByte, lowerByte]; // Return as [higher, lower] assuming Big Endian byte order
}

Explanation

- Integer Splitting: The function starts by taking a measurement (measurements parameter), assumed to be a single integer for simplicity. This integer is then split into two bytes:
- The lower byte is extracted by applying a bitwise AND operation with 0xFF, which effectively masks out all but the lower 8 bits of the integer.
- The higher byte is obtained by first shifting the integer 8 bits to the right (moving the 9th to 16th bits into the 1st to 8th bit positions) and then applying the same masking operation.

- Byte Order: The function returns the bytes in an array. The order of bytes ([`higherByte`, `lowerByte`]) assumes a Big Endian format, where the most significant byte (MSB) comes first. If your system uses Little Endian format, you would reverse the order in the returned array.

Usage Example

You can use the following example locally to test with your own development environment.

var myMeasurement = 0x1234; // Example integer to be split
var port = 1; // Example port number, not used in the split
var bytes = Encoder(myMeasurement, port);
console.log(bytes); // Logs: [18, 52] for Big Endian byte order

This example demonstrates using the Encoder function to split a 16-bit integer into two bytes, which are then ready to be transmitted or further processed according to your application's needs.

Important Disclaimer

Please note that the encoder for downlink messages must match the specification of the customer's IoT end devices. As all devices are different, it is the user's responsibility to encode the downlink according to the structure of the device. We are not responsible for ensuring compatibility between the encoded data and any specific device's requirements. However, should you require assistance with encoding data for your specific IoT devices, we offer paid development support. Please contact us for more information and assistance.

Updated on: 02/02/2024