Professional Courses
Industry-relevant training in Business, Technology, and Design to help professionals and graduates upskill for real-world careers.
Categories
Interactive Games
Fun, engaging games to boost memory, math fluency, typing speed, and English skillsβperfect for learners of all ages.
Typing
Memory
Math
English Adventures
Knowledge
Interactive Audio Lesson
Listen to a student-teacher conversation explaining the topic in a relatable way.
Keyboard Configurations
Unlock Audio Lesson
Signup and Enroll to the course for listening the Audio Lesson
Today, we're diving into keyboard configurations for microcontroller interfaces. Can anyone tell me what types of keyboards might be used?
I think there are lead-per-key keyboards?
Correct! Lead-per-key keyboards are great for simple applications with few keys. What about larger applications?
Matrix keyboards! They allow for more keys by organizing them in rows and columns.
Exactly! The matrix keyboard is often used because it efficiently handles many keys. Can anyone explain how it manages multiple key presses?
The microcontroller scans each row and column to see which keys are pressed.
Great point! This scanning method is essential to determine the active key. Remember, we often need to handle contact bounce. What is contact bounce?
It's when a key press generates multiple signals due to the physical bouncing of the switch!
Exactly, and to mitigate that, we can implement debouncing. Can anyone tell me how we could do that?
Using a resistor-capacitor (RC) circuit or a Schmitt trigger. Right?
That's right! Now letβs summarize: We discussed lead-per-key, coded, and matrix keyboards and their workings. We learned how to handle contact bounce through different methods. Great participation, everyone!
Contact Bounce Considerations
Unlock Audio Lesson
Signup and Enroll to the course for listening the Audio Lesson
Today, let's focus on contact bounce issues. Why is it important to address this when interfacing keyboards?
If we don't, the microcontroller might read multiple presses when just one happened!
Exactly! High-quality keyboards provide lower bounce periods compared to cheaper options. What bounce periods should we expect?
1 to 5 milliseconds for good ones, and tens of milliseconds for low-quality ones!
Correct! To manage contact bounce, we can either use hardware or software debouncing. Can anyone describe the hardware method?
We can use an RC circuit to smooth out the signal?
Well done! This creates a delay, allowing any bouncing to settle. What about software debouncing?
We could introduce a delay after detecting a key press to ensure it's stable before processing.
Exactly! Summarizing, we learned that contact bounce can lead to incorrect readings and methods exist to handle it. Excellent discussions today!
Multiple Key Press Handling
Unlock Audio Lesson
Signup and Enroll to the course for listening the Audio Lesson
Let's discuss how keyboards handle multiple key presses. Why is it significant in keypads?
To make sure the microcontroller responds correctly to all pressed keys, right?
Exactly! Systems must avoid executing invalid inputs when multiple keys are pressed. What approaches can be taken?
Only the first valid press should be executed.
Or we follow a specific sequence or pattern!
Great details! This brings us to two concepts: **two-key lockout**, which only allows one key press at a time, and **N-key rollover**, which processes valid sequences. Can you summarize these?
Two-key lockout allows just one key, while N-key rollover can handle multiple keys but only executes valid patterns.
Excellent summary! For the final recap: we covered the significance of managing multiple key presses, highlighting two-key lockout and N-key rollover. Fantastic engagement today!
Introduction & Overview
Read a summary of the section's main ideas. Choose from Basic, Medium, or Detailed.
Quick Overview
Standard
The section elaborates on different keyboard configurations including lead-per-key, coded, and matrix keyboards, with an emphasis on practical issues like contact bounce and multiple key presses.
Detailed
Interfacing Keyboards
In microcontroller systems, keyboards play a crucial role in data entry. This section outlines three primary configurations: lead-per-key, coded, and matrix keyboards. Lead-per-key keyboards are suitable for simple inputs with fewer keys, while coded keypads are typically used in telephonic applications and can handle a maximum of 16 keys. The matrix keyboard, featuring keys arranged in rows and columns, is more prevalent when a larger number of keys (usually over 10) is needed.
Key Considerations
When interfacing keyboards, several factors must be taken into account:
1. Contact Bounce: This refers to the undesirable multiple make-and-break signals when a key is pressed. High-quality keyboards have bounce periods of 1-5 ms, while low-cost ones can have periods in the tens of milliseconds. Addressing contact bounce can be achieved through hardware (using RC or Schmitt trigger circuits) or software debouncing, typically involving a delay after a key press.
- Multiple Keys: Systems must manage valid multiple-key presses without executing invalid routines. The first valid key press should always trigger a response.
- Keyhold Types: There are two actuation methods: two-key lockout, allowing only one key press to register, and N-key rollover, which processes multiple pressed keys but only executes routines for valid patterns.
The intricate way in which keys are accessed in matrix keypads is crucial; each column remains HIGH while scanning each row to detect presses, providing a robust method for identifying which key is activated.
Youtube Videos
Audio Book
Dive deep into the subject with an immersive audiobook experience.
Keyboard Configurations
Unlock Audio Book
Signup and Enroll to the course for listening the Audio Book
Keyboards are used to enter data, values, etc., into the microcontroller system. They are generally available in three configurations, namely the lead-per-key keyboard, the matrix keyboard, and the coded keyboard. Lead-per-key or linear keyboards are used when very few keys have to be sensed. Coded keypads are generally used in telephonic applications. They are high-quality durable keyboards and permit a multiple key press to be detected easily. They are used when the number of keys is 16 or less, as they are very expensive. The most commonly used keyboard is the matrix keyboard where the keys are arranged in a matrix, with keys in the same row and column sharing the same access lines.
Detailed Explanation
There are three main configurations of keyboards that can be interfaced with a microcontroller. The first type is a lead-per-key keyboard, which is generally simple and ideal for applications with fewer keys. The second type, coded keypads, are often found in telephones and high-quality applications that require durability and can recognize multiple keys pressed at once. However, they tend to be expensive and are usually limited to 16 keys or less. The most common type of keyboard used is the matrix keyboard, which organizes the keys in a grid format. This arrangement allows for efficient use of available input lines by enabling multiple keys to be sensed through shared rows and columns.
Examples & Analogies
Think of a lead-per-key keyboard as a simple door with a single lock that only opens if you use that specific key, suitable for small applications. In contrast, envision a coded keypad as a more advanced security system, much like a heavy-duty door lock that can accept various combinations, suitable for telephones. Finally, a matrix keyboard can be likened to a computer keyboard where multiple keys share connections to save space, allowing you to input various commands efficiently.
Key Considerations When Interfacing Keyboards
Unlock Audio Book
Signup and Enroll to the course for listening the Audio Book
When the keyboards are connected to a microcontroller, following factors must be considered:
- Contact bounce. Contact bounce refers to multiple βmakeβ and βbreakβ oscillations of contact during the key-pressing operation. Good-quality keyboards have bounce periods of 1β5 ms, whereas low-cost keyboards have bounce periods of tens of milliseconds. If the bounce is not taken into consideration, the microprocessor responds as if the key has been pressed and released several times when in fact it has been pressed only once. Contact debouncing through either a hardware or a software routine is done to avoid the undesirable multiple-contact effects during a key closure, so that it appears as a single ON or OFF operation. Hardware debouncing is done using an RC circuit or a Schmitt trigger circuit.
- Multiple keys. If more than one key is pressed, then only routines corresponding to valid multiple-key presses should be executed. Also, the first valid keypress pattern is executed.
- Key hold. There are two types of keyboard actuation, namely the two-key lock-out and the N-key rollover.
Detailed Explanation
When interfacing keyboards with a microcontroller, a few critical factors must be addressed. The first factor is contact bounce, which occurs when the switch's internal contacts physically bounce when pressed, leading the microcontroller to register multiple presses instead of one. Quality keyboards minimize this issue; however, it's still essential to manage it either through hardware solutions (e.g., an RC circuit) or software routines that introduce a short delay. The second consideration is handling multiple keys being pressed at the same time; the system should recognize valid combinations and ignore invalid ones. Lastly, the type of actuation is crucial; two-key lock-out allows only one key press at a time, while N-key rollover supports registering multiple key presses simultaneously.
Examples & Analogies
Imagine a crowded elevator where people press multiple buttons. If everyone tries to press their button at once, it can result in confusion - the system might falsely register multiple requests. Proper debouncing is like employing a rule where only the first button pressed is registered, while the elevator maintains its efficiency without being overwhelmed by multiple simultaneous commands.
Connection of Matrix Keypad
Unlock Audio Book
Signup and Enroll to the course for listening the Audio Book
Figure 14.29 shows the connection of a 16-key matrix keypad with a microcontroller. Here, each column and row access line is connected to the microcontroller pin. The columns are generally at a HIGH level. The row lines are configured as output lines and the column lines are used as scan lines. The key actuation is sensed by sending a LOW to each row one at a time through a software routine via the row1, row2, row3, and row4 lines. The column lines are checked for each row to see whether any of the normally HIGH column lines are pulled LOW.
Detailed Explanation
In interfacing a matrix keypad, the setup involves connecting each column and row of keys to the microcontroller. The columns are usually maintained at a HIGH state, while the rows are set as outputs. To determine which key is pressed, the microcontroller sequentially sends a LOW signal to each row. By monitoring the column lines for a change to LOW while a row is active, it can identify which specific key has been pressed based on the active row and column combination.
Examples & Analogies
Think of the matrix keypad as a group of light switches connected to a single circuit. When you want to find out which switch is on, you turn off each line one at a time and check to see which light responds. This technique of focusing on one switch at a time allows you to effectively pinpoint exactly which switch is turned on without getting confused by the others.
Definitions & Key Concepts
Learn essential terms and foundational ideas that form the basis of the topic.
Key Concepts
-
Keyboard Configurations: Different types including lead-per-key, coded, and matrix keyboards are essential for various applications.
-
Contact Bounce: A critical issue in key interfacing that must be managed to ensure accurate keypress readings.
-
Debouncing Techniques: Methods for eliminating contact bounce effects include hardware and software approaches.
-
Multiple Key Press Handling: Specific strategies such as two-key lockout and N-key rollover ensure proper input processing.
Examples & Real-Life Applications
See how the concepts apply in real-world scenarios to understand their practical implications.
Examples
-
A lead-per-key keyboard might be used in a simple calculator, where each key directly connects to a microcontroller pin.
-
A matrix keypad configuration might be utilized in an ATM machine where numerous keys are required for user interaction.
Memory Aids
Use mnemonics, acronyms, or visual cues to help remember key information more easily.
π΅ Rhymes Time
-
Keypressed just once, / No bouncing to punch. / Two-key lockout, / Clear? Let's shout!
π Fascinating Stories
-
Imagine a busy bank teller who needs to quickly enter data using a matrix keyboard. To avoid chaos from multiple key presses, they only allow valid transactions, efficiently processing customers' requests one by one.
π§ Other Memory Gems
-
Remember B.D.K.: Bounce -> Debounce -> Keys. Each step ensures clear communication with the microcontroller.
π― Super Acronyms
MEMOKEY
- Manage Every Multiple Operation with a KEYboard interface
- ensuring efficiency.
Flash Cards
Review key concepts with flashcards.
Glossary of Terms
Review the Definitions for terms.
-
Term: Leadperkey keyboard
Definition:
A simple keyboard design where each key has its own physical connection to the microcontroller.
-
Term: Coded keypad
Definition:
A high-quality keyboard used in applications like telephony, supporting 16 or fewer keys.
-
Term: Matrix keyboard
Definition:
A configuration where keys are arranged in a matrix of rows and columns for efficient scanning.
-
Term: Contact bounce
Definition:
The rapid on-off switching that occurs when a key is pressed, leading to multiple signals to the microcontroller.
-
Term: Debouncing
Definition:
Techniques used to eliminate the effects of contact bounce.
-
Term: Twokey lockout
Definition:
A key actuation method that allows only one key press to register at a time.
-
Term: Nkey rollover
Definition:
A method permitting multiple keys to be pressed simultaneously but registering only valid sequences.