The 4028 decoder is an important component in many digital circuits and systems. In this article, we will explore what a 4028 decoder is, how it works, and some practical applications.

What is a 4028 Decoder?

A 4028 decoder is an integrated circuit (IC) that converts binary information from n input lines to a maximum of 2^n unique output lines. The 4028 contains a 5-to-32 line decoder, meaning it has 5 input pins and 32 output pins.

The truth table for a 4028 is:

So in simple terms, the 4028 takes a 5-bit binary number and activates one of the 32 outputs corresponding to that number.

How the 4028 Decoder Works

The 4028 contains logic gates internally that decode the inputs and set the appropriate output. Some key points:

• There are 5 input pins labeled A, B, C, D, E
• When all inputs are low (00000), output 1 is high
• As the binary count increases on the inputs, different output pins are activated in sequence
• The IC uses power from Vcc and ground pins to power the internal logic
• Output pins have active-low logic, meaning a low voltage indicates an active output

Applications of the 4028 Decoder

Some common uses of the 4028 decoder include:

• Driving indicator LEDs – The outputs can directly drive LEDs to show a binary count.
• Memory addressing – In memory systems, it can decode addresses to activate a particular byte or word.
• 7-segment displays – With additional logic, it can drive the segments of 7-segment LED displays.
• Digital logic – Decoders are used to generate control signals and route data between registers, counters, and other logic.

Example Circuit with 4028

Here is a simple example of using a 4028 to drive 8 LEDs:

This uses 3 input bits to generate 8 unique outputs and flash the corresponding LED when active. More complex displays and logic can be driven with the additional outputs.

Summary

• The 4028 IC provides a 5-to-32 line decoding function for digital logic systems
• It activates one of 32 outputs based on a 5-bit binary input code
• This allows it to drive displays, memory, and other components that require unique selection
• With power, ground, inputs, and outputs connected properly, the 4028 can enable a wide range of applications.

Frequently Asked Questions

What is the difference between the 4028 and similar decoder ICs like the 4514?

The main difference is the number of inputs and outputs. The 4028 has 5 inputs and 32 outputs. The 4514 has 4 inputs and 16 outputs. So the 4028 can decode more unique addresses than the 4514.

How do I activate multiple outputs on the 4028 at the same time?

The 4028 is designed to have only one output active at a time. To activate multiple outputs, you would need additional external gates or logic to combine the outputs.

Can the 4028 sink or source current on the outputs?

The 4028 can sink current on its active-low outputs. Each output can sink up to 16mA. Sourcing current requires external pull-up resistors connected to the supply voltage.

Is the 4028 compatible with microcontrollers like Arduino?

Yes, the 4028 can be driven by a microcontroller’s digital I/O pins. The 5 address lines would connect to arbitrary digital pins. The outputs could sink LEDs or drive external logic.

How fast can the 4028 operate or switch outputs?

The 4028 can operate at speeds up to 15-20 MHz typically, making it compatible with fast digital systems and microcontrollers. The propagation delay is around 25 nanoseconds.