- Keyboard Encoder Definition: A keyboard encoder is a device that converts signals from a keyboard matrix into serial data for external devices.
- Types of Encoders: There are hardware-based and software-based keyboard encoders.
- Hardware-Based Encoders: These use integrated circuits for fast and reliable encoding but are less flexible.
- Software-Based Encoders: These run on microcontrollers, offering flexibility and customization.
- Applications: Keyboard encoders are used in various devices, including computers, industrial keyboards, and custom keyboards.
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 regularly to detect which key is pressed or released, then encodes the event for the external device. Numeric keypads often use binary-coded decimal (BCD), a four-bit representation of a digit from 0 to 9, while full keyboards use scan codes that uniquely identify each key. The code travels to the host over USB or PS/2.
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 use logic gates, diodes, resistors, capacitors and flip-flops to encode signals. Built for specific keyboard layouts, they map row and column coordinates to BCD or scan codes through fixed matrix tables. Fast and reliable, they give up flexibility and need extra components to talk to external devices.
One hardware example is the SK5120, a low-power programmable encoder IC with USB and PS/2 support. It can be programmed for custom keyboard layouts and can emulate mouse actions from key presses, with support for an external PS/2 pointing device.
Another example is the KE24, a programmable PS/2 interface that scans a matrix up to 12 x 12 or 24 individual inputs, with an RS-232 serial port alongside. Custom keystrokes and macro sequences load into it through Windows® software.
Software-Based Keyboard Encoders
Software-based keyboard encoders are programs running on microcontrollers or microprocessors with access to the keyboard matrix. Software algorithms scan the matrix, detect key events and generate BCD or scan codes. These encoders are more flexible and customizable than hardware ones but need more programming skills and memory resources.
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.
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 turns the raw grid of a keyboard matrix into codes a host understands, whether that happens in dedicated silicon or in software on a microcontroller. Hardware encoders trade flexibility for speed and simplicity; software encoders do the opposite. Between them they sit inside everything from laptops and POS terminals to custom mechanical keyboards.
