Keyboard Encoder: Definition, Types, and Applications

What is a Keyboard Encoder?

A keyboard encoder is a device that converts the signals from a keyboard matrix into a serial format data word that can be transmitted to an external device, such as a computer or a microcontroller. A keyboard matrix is a grid of rows and columns of switches that represent the keys on a keyboard. Each switch has a unique combination of row and column coordinates that correspond to a specific key.

A keyboard encoder scans the keyboard matrix periodically and detects which key is pressed or released. It then encodes the row and column information of the key into a binary-coded decimal (BCD) code or a scan code, depending on the type of encoder. A BCD code is a four-bit representation of a decimal digit from 0 to 9, while a scan code is a unique identifier for each key on the keyboard. The encoder sends the code to the external device through a serial interface, such as USB or PS/2.

truth table of keyboard encoder

Types of Keyboard Encoders

There are two main types of keyboard encoders: hardware-based and software-based.

Hardware-Based Keyboard Encoders

Hardware-based keyboard encoders are integrated circuits (ICs) that perform the encoding function using logic gates, diodes, resistors, capacitors, and flip-flops. They are usually designed for specific keyboard layouts and have fixed matrix tables that map the row and column coordinates to the BCD or scan codes. Hardware-based keyboard encoders are fast, reliable, and easy to use, but they are also inflexible and require additional components for interfacing with the external device.

logical circuit of keyboard encoder

An example of a hardware-based keyboard encoder is the SK5120, which is a low-power USB programmable keyboard encoder IC with an external PS/2 port and KeyMouse support. The SK5120 can be programmed to any keyboard with four matrix tables for FN and NUMLOCK cases, so it is suitable for custom keyboard solutions. It also supports one external PS/2 device, such as a touchpad or a pointing stick, and can emulate PS/2 mouse action with its built-in 8-direction KeyMouse feature.

logical circuit of keyboard encoder

Another example of a hardware-based keyboard encoder is the KE24, which is a programmable PS/2 interface that scans a matrix up to 12 x 12 or as many as 24 individual inputs. It also has an RS-232 serial port for communication with other devices. The KE24 can be programmed with custom keystrokes or macro sequences for each input using Windows® application software.

Software-Based Keyboard Encoders

Software-based keyboard encoders are programs that run on microcontrollers or microprocessors that have access to the keyboard matrix. They use software algorithms to scan the matrix, detect the key events, and generate the BCD or scan codes. Software-based keyboard encoders are more flexible and customizable than hardware-based ones, but they also require more programming skills and memory resources.

logical circuit of keyboard encoder

An example of a software-based keyboard encoder is the Arduino Keyboard Library, which allows an Arduino board to act as a USB HID (Human Interface Device) keyboard. The library uses the Arduino pins to connect to the keyboard matrix and provides functions to read the key states and send keystrokes to the computer. The library also supports modifier keys, such as SHIFT, CTRL, ALT, etc.

logical circuit of keyboard encoder

Applications of Keyboard Encoders

Keyboard encoders are widely used in various applications that require human-machine interaction through keyboards, such as:

  • Computers
  • Laptops
  • Netbooks
  • Industrial keyboards
  • Point-of-sale (POS) terminals
  • Portable devices
  • Custom keyboards

Keyboard encoders enable keyboards to communicate with different devices using standard protocols, such as USB or PS/2. They also allow keyboards to have additional features, such as macro keys, custom keys, mouse emulation, etc.

Conclusion

A keyboard encoder is a device that converts the signals from a keyboard matrix into a serial format data word that can be transmitted to an external device. There are two main types of keyboard encoders: hardware-based and software-based. Hardware-based keyboard encoders are integrated circuits that perform the encoding function using logic components, while software-based keyboard encoders are programs that run on microcontrollers or microprocessors that have access to the keyboard matrix. Keyboard encoders are widely used in various applications that require human-machine interaction through keyboards.

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