Digital Electronics - Keyboard Encoders

A keyboard encoder is an electronic device used in computer peripherals, mainly in keyboards, to convert keystrokes into digital signals. In this chapter, we will discuss the definition, types, and applications of keyboard encoders. Lets start with the basic introduction to keyboard encoders.

What is a Keyboard Encoder?

An electronic circuit which is used to translate keystrokes from physical keyboards into digital signals that a processing device can understand and process is known as a keyboard encoder. It is basically a type of encoder that encodes the information represented in alphanumeric form into digital or binary form.

A keyboard encoder acts as an interface between the physical keyboard and the processing unit of a computing system. The primary function of a keyboard encoder is to detect the key presses and encode them into binary format. This encoded signal is then sent to the processing system through a communication interface like USB, Bluetooth, etc.

Keyboard encoders are essential components in input devices like keyboards as they allow conversion of human data in machine language.

Applications of Keyboard Encoders

Keyboard encoders are mainly used in input devices like keyboards to convert physical keystrokes into digital signals that a processing device can process.

Here are some examples of applications of keyboard encoders −

• Keyboards used in desktop computers and laptops.
• Keyboard encoders are also used in gaming peripherals like gaming keyboards.
• Keyboard encoders are also used in control panels and human-machine interfaces used in industrial control systems and automation equipment.
• Keyboard encoders are also equipped in various medical devices such as medical imaging devices, patient monitoring devices, diagnostic systems, etc.
• Keyboard encoders are also important components in point-of-sales (POS) devices.
• Keyboard encoders are utilized in data entry devices like scanners, handheld devices, etc.

Keyboard encoders are essential component in input devices allowing users to input data into a processing system. They create an interface between the input hardware and digital processing unit. The above section highlights some common examples where the keyboard encoders are used.

Let us understand the circuit and working of a typical 8421 BCD keyboard encoder which is an important element in various keyboard designs. The 8421 BCD keyboard encoder provides a simple and efficient way of encoding decimal digit into binary format for processing using digital systems like microcontrollers.

8421 BCD Keyboard Encoder

The 8421 BCD keyboard encoder is a type of encoder used in keyboards and many other digital devices where decimal digits are need to be converted into a binary format or BCD (binary-coded decimal).

The diode matrix of the 8421 BCD keyboard encoder is shown in the following figure −

This keyboard encoder uses SR flip-flops to store the BCD output bits designated as Q₈Q₄Q₂Q₁.

When a key corresponding to any decimal digit between "0" and "9" is pressed, the power supply V_CC turns ON the appropriate diodes which are further connected to the SET (S) and RESET (R) inputs of the flip-flops.

In this circuit, all the diodes are connected in a manner that each SR flip-flop SET or RESET to produce a combination of 4-bits representing the corresponding decimal digit in BCD format.

Let us take an example to understand the working of this 8421 BCD keyboard encoder.

When we press the key "0", the diodes connected to the R inputs of the flip-flops Q₈, Q₄, Q₂, and Q₁ are forward biased. Hence, the output will be 0000.

Similarly, when we press the key "3", the diodes connected to the R inputs of Q₈ and Q₄ are forward biased and the diodes connected to the S inputs of Q₂ and Q₁ are forwards. Hence, this produces an output as 0011.

The keyboard encoder also works in the same way for all other decimal digits.

Conclusion

In this chapter, we explained the functions and applications of keyboard encoder. Also, we highlighted the construction and working of a simple 8421 BCD keyboard encoder which is used in various small electronic devices like ATMs, POS terminals, mobile phones, and many other electronic devices.