How do Computer Keyboards Work? 🤔⌨⌨🛠

Summary

This video script explores the engineering marvels behind basic computer keyboards, focusing on cost reduction. It dissects an inexpensive keyboard with only 8 critical parts, costing as low as $1.57 each, and explains how it functions using a simple matrix system. The script contrasts this with a high-end mechanical keyboard, costing over 50 times more, revealing the intricate mechanisms behind its tactile feedback and clicking sound. The video also touches on laptop keyboards and emphasizes the importance of engineering education.

Takeaways

• 😲 Basic computer keyboards have surprisingly impressive engineering, particularly in cost reduction.
• 💰 The inexpensive keyboard is made up of only 8 critical parts, allowing for bulk purchases as low as $1.57 each.
• 🔍 Inside the cheap keyboard: a rubber sheet with domes, three plastic sheets with conductive wires, and a simple circuit board with components.
• ⚙️ The keyboard's functionality relies on a matrix system where keys press domes to bridge conductive traces on plastic sheets.
• 🔋 The keyboard matrix uses a method of scanning columns with 3 volts and detecting row inputs to identify key presses.
• 🔌 The microprocessor sends key data to a 2.4 GHz transceiver, utilizing printed planar antennas for wireless communication.
• 💡 Mechanical keyboards, costing over 50 times more, have a different internal mechanism, including a spring and metal contacts for each key.
• 🎉 The clicking sound in mechanical keys comes from the metal contacts hitting each other when the key is pressed.
• 🛠️ Mechanical keyboards offer a more tactile feel due to their intricate internal components, which also contribute to their higher cost.
• 📱 Laptop keyboards use a scissor switch mechanism with rubber domes for a lower profile, differentiating them from desktop keyboards.

Q & A

How many critical parts are inside the inexpensive keyboard mentioned in the script?

The inexpensive keyboard has only 8 critical parts inside.

What are the main components of the inexpensive keyboard's key mechanism?

The main components of the key mechanism in the inexpensive keyboard are a rubber sheet with domes under each key and three plastic sheets, with conductive wires printed on the top and bottom sheets.

How does the inexpensive keyboard detect which key has been pressed?

The inexpensive keyboard detects which key has been pressed by bridging the connection between the top and bottom plastic sheets when a key is pressed, allowing a 3-volt signal to travel from the bottom sheet, through the pressed key, to the top sheet, and back to the microprocessor.

What is a keyboard matrix and how does it relate to the inexpensive keyboard?

A keyboard matrix is a grid-like organization of the keyboard's traces, with the bottom traces forming columns and the top traces forming rows. The inexpensive keyboard uses this matrix to determine which key is pressed by correlating the active column with the input row.

How does the inexpensive keyboard solve the problem of identifying which key is pressed when multiple keys are pressed simultaneously?

The inexpensive keyboard solves this problem by sending a cycle of pulses that turn off one column at a time to determine which key in a row is pressed, with these pulses sent for 65 microseconds to each column, once every 4 milliseconds.

What is the purpose of the 2.4 gigahertz transceiver in the inexpensive keyboard?

The 2.4 gigahertz transceiver in the inexpensive keyboard is used to send the data about which keys are pressed to the connected device using the printed planar antennas.

What is the main difference between the inexpensive keyboard and the mechanical keyboard discussed in the script?

The main difference is that the mechanical keyboard has a more complex and durable key mechanism with a tactile feel and a clicking sound, whereas the inexpensive keyboard uses a simpler and less expensive mechanism with rubber domes.

What is the function of the stem and slider in the mechanical keyboard's key mechanism?

In the mechanical keyboard's key mechanism, the stem and slider work together to move one of the metal contacts away from the other when a key is pressed, creating a connection and causing a click sound. When the key is released, the spring pushes everything back up, separating the metal contacts.

Why are mechanical keyboards more expensive than the inexpensive keyboards?

Mechanical keyboards are more expensive due to the larger printed circuit board and the intricate mechanism inside each key, which provides a more tactile feel and a clicking sound when pressed.

What is the purpose of the scissor switch mechanism in laptop keyboards?

The scissor switch mechanism in laptop keyboards allows for a lower profile while still providing a key mechanism with rubber domes, making it suitable for the thinner design of laptops.

How does the inexpensive keyboard's design highlight the importance of engineering in cost reduction?

The inexpensive keyboard's design highlights the importance of engineering in cost reduction by using only 8 critical parts and a simple key mechanism, allowing the keyboard to be produced and sold at a very low cost while still being functional and durable.

Outlines

00:00

🔍 Inside the Inexpensive Keyboard: Engineering for Cost Reduction

This paragraph delves into the engineering marvels of a basic computer keyboard, focusing on cost reduction rather than high-tech features. The keyboard is composed of only 8 critical parts, which allows for mass production at an incredibly low cost of $1.57 each. The components include a rubber sheet with domes, three plastic sheets with conductive wires, and a few additional parts like batteries and a printed circuit board (PCB) with a microprocessor. The operation is based on a simple mechanism where key presses create a connection between the conductive layers, allowing the microprocessor to detect which key was pressed. The paragraph also introduces the concept of a keyboard matrix, explaining how the microprocessor uses a grid system to determine the exact key pressed, and discusses the energy-efficient method of scanning columns to identify key presses.

05:02

🎥 Exploring the High-End Mechanical Keyboard: A World of Difference

The second paragraph contrasts the inexpensive keyboard with a high-end mechanical keyboard, which costs over 50 times more. It describes the internal components of the mechanical keyboard, which include a large PCB with mechanical keys, LEDs for lighting, and a unique tactile and auditory feedback mechanism. Each key in a mechanical keyboard contains a stem, slider, switch housing, spring, and metal contacts that create a clicking sound when pressed. The paragraph explains how the key press engages the slider, causing the metal contacts to connect and create a click, and how the spring mechanism resets the key. It also touches on the practicality and preferences that justify the higher cost of mechanical keyboards and briefly mentions laptop keyboards with scissor switch mechanisms.

10:02

📚 Engineering Education: The Backbone of Technological Advancement

The final paragraph serves as a conclusion and a call to action for engineering education. It emphasizes the importance of understanding the cost differences and engineering behind everyday technologies like keyboards. The paragraph also acknowledges the support from Patreon and YouTube Membership Sponsors, which enables the creation of educational content. It encourages viewers to subscribe, like, and share the video, and provides a prompt to watch more videos by Branch Education, which produces 3D animations to explore the technology behind modern innovations.

Keywords

💡Engineering

Engineering refers to the application of scientific principles to design, build, and maintain structures, machines, devices, systems, materials, and processes. In the context of the video, engineering is discussed in terms of cost reduction and the design of a basic computer keyboard that is both durable and functional at a minimal cost. The video highlights how engineering has made it possible to produce keyboards with only 8 critical parts, significantly reducing production costs.

💡Cost Reduction

Cost reduction is the process of minimizing expenses or production costs while maintaining quality. The video emphasizes the impressive engineering feat of cost reduction in keyboard manufacturing, where the number of components has been minimized to produce keyboards at a very low cost, as low as $1.57 each. This is achieved by reducing the number of parts and simplifying the design.

💡Critical Parts

Critical parts are essential components that are vital for the functioning of a device. The video mentions that the inexpensive keyboard has only 8 critical parts, including a rubber sheet with domes, three plastic sheets with conductive wires, batteries, a clamping bracket, and a printed circuit board with a microprocessor. These parts are crucial for the keyboard's functionality and are highlighted as the core of the engineering that allows for cost reduction.

💡Mechanical Keyboard

A mechanical keyboard is a type of keyboard that uses mechanical switches to provide tactile feedback and audible clicks when keys are pressed. In the video, a comparison is made between the inexpensive keyboard and a mechanical keyboard that costs over 50 times more. The mechanical keyboard is shown to have a more complex internal mechanism, including a keycap, stem, slider, switch housing, spring, and metal contacts, which contribute to its higher cost and different tactile feel.

💡Rubber Dome

A rubber dome is a flexible membrane that, when pressed, completes an electrical circuit, triggering a keypress. The video explains that the inexpensive keyboard uses a rubber sheet with domes under each key, which, when pressed, pushes a conductive circle from the top sheet into the bottom sheet, creating a connection that signals a keypress to the microprocessor.

💡Conductive Wires

Conductive wires are wires that allow the flow of electric current. In the video, conductive wires are printed onto the top and bottom plastic sheets of the keyboard. These wires, along with the rubber domes and the microprocessor, form a circuit that detects when a key is pressed and sends the corresponding signal.

💡Microprocessor

A microprocessor is a small computer on a single integrated circuit that processes data and controls operations in electronic devices. The video describes how the microprocessor in the keyboard's printed circuit board applies voltage to the traces on the bottom sheet and monitors the top sheet for keypresses. It plays a central role in detecting which key is pressed and sending that information to the computer.

💡Keyboard Matrix

A keyboard matrix is a grid layout of the keyboard's keys, with rows and columns that correspond to the electrical connections for each key. The video uses the concept of a keyboard matrix to explain how the microprocessor can determine which key is pressed by monitoring the voltage along the columns and rows. This grid system allows for a compact and cost-effective design.

💡2.4 Gigahertz Transceiver

A 2.4 gigahertz transceiver is a device that sends and receives signals in the 2.4 GHz frequency band, commonly used for wireless communication. The video mentions that the microprocessor sends keypress data to the 2.4 GHz transceiver, which then communicates wirelessly with the computer. This component is part of what allows the keyboard to function without physical connections to the computer.

💡Scissor Switch Mechanism

A scissor switch mechanism is a type of keyswitch used in some laptop keyboards that provides a stable and low-profile keystroke. The video briefly mentions this mechanism in the context of laptop keyboards, which, along with rubber domes, allows for a thinner keyboard design. This mechanism is different from the mechanical switches found in mechanical keyboards and contributes to the lower profile and cost of laptop keyboards.

Highlights

Basic computer keyboards have surprisingly impressive engineering for cost reduction.

A cost-effective keyboard has only 8 critical parts inside.

These keyboards can be bought in bulk for as little as $1.57 each.

The engineering feat is creating durable, functional keyboards at nearly zero cost.

The keyboard consists of 148 parts, with 8 being critical.

Components include a rubber sheet with domes, three plastic sheets, and a few electronic parts.

The top and bottom plastic sheets have conductive wires printed on them.

The middle sheet acts as a spacer with holes cut out.

The remaining components are batteries, a clamping bracket, and a small printed circuit board.

The microprocessor applies 3 volts to the traces on the bottom sheet.

When a key is pressed, it bridges the connection between the top and bottom sheets.

The keyboard matrix is visualized as a grid with columns and rows.

The microprocessor uses a scanning method to determine which key is pressed.

The mechanical keyboard is opened to compare with the inexpensive keyboard.

Mechanical keyboards have a different tactile feel and make a clicking sound.

Inside mechanical keys, there's a stem, slider, switch housing, spring, and metal contacts.

The slider's unique shape pushes one contact away from the other when a key is pressed.

The stem and slider allow for a small distance of travel before engagement.

Laptop keyboards use a scissor switch mechanism with rubber domes.

The video highlights the cost difference and engineering in two similar items.

Transcripts

You might not think it, but basic computer  keyboards have a surprisingly impressive  

amount of engineering inside. We’re not  talking about incredible engineering  

like a rocket that can land itself or a  stealth aircraft that can evade radar;  

rather, we’re talking about the engineering of  cost reduction. Specifically, this keyboard has  

only 8 critical parts inside, essentially removing  all the components’ costs so that you can buy them  

in bulk for as little as 1 dollar and 57 cents  each! Engineering something that is durable,  

functional, and costing next to nothing is  indeed a feat on its own. So, let’s look inside  

this dirt-cheap keyboard and see how only a few  critical components enables it to work. After that  

we’ll open a mechanical keyboard that costs over  50 times as much and see the difference as well as  

find out what causes that clicking sound inside  the mechanical keys. So, let’s jump right in. 

This inexpensive keyboard is assembled from 148  parts, and almost all the parts are the keys,  

screws, and the top and bottom plastic casing,  leaving us only 8 critical parts inside. These  

components are a rubber sheet with domes under  each key and three plastic sheets. The top and  

bottom sheets have conductive wires printed  onto them, with dots under each key, and the  

middle sheet acts as a spacer with holes cut out  of it. The remaining 4 components are 2 batteries,  

a bracket to clamp down the plastic sheets,  and a small printed circuit board which has a  

simple microprocessor, a crystal oscillator,  a switch, a 2.4 gigahertz planar antenna,  

a pair of wires to connect to the batteries, and  a set of conductive lines to connect to the wires  

printed on the top and bottom plastic sheets. So now that we’ve seen the few components inside,  

how do they work? Well, the main idea is that  the batteries and microprocessor apply 3 volts  

to all the traces on the bottom sheet, while  all the traces on the top sheet are actively  

being monitored by the processor on the PCB. When  a key is pressed, it presses on the rubber dome,  

which pushes the conductive circle from the top  sheet down through the air gap created by the  

middle sheet and into the circle on the bottom  sheet, thereby bridging the connection between  

top and bottom plastic sheets. The 3 volts then  travels along the conductive trace of the bottom  

sheet through the hole of the key that has been  pressed, and into the top sheet’s trace, and then  

returns back to the PCB and microprocessor where  it’s sensed. When you let your finger off the key,  

the rubber dome returns the key to the un-pressed  position thereby opening the connection. 

On the top sheet of plastic are 12 traces  and on the bottom sheet are 11 traces,  

with each trace traveling to a different set of  keys. It’s visually hard to see here, so let’s  

reorganize these traces into a grid, also called  a keyboard matrix, with the bottom traces forming  

the columns and the top traces forming the rows.  Just as before the microprocessor outputs 3 volts  

along each column while actively monitoring the  in-puts along each row. With this reorganization,  

you can more easily see that, as you press the  Y key, 3 volts is sent out along the 4th column,  

and returned along the 2nd row, and thus the  processor can tell that the Y key was pressed.  

Or with the B key, 3 volts is output along  the 8th column, and input through the 1st  

row. With 11 columns and 12 rows, we can have  a maximum of 132 keys, which works out well,  

because the keyboard has only 111 keys. However, if you haven’t noticed, there’s  

actually a major problem with this keyboard  matrix. That is: if we have 3 volts running  

along all these columns and we press a key, 3  volts will return along a row. However, because  

each of these columns output the same 3 volts, how  do we know which key in the row was pressed? Well,  

there are a few solutions to this problem. One  solution is to quickly scan 3 volts along each  

of the 11 columns, so that at any given time  only one column is active. By correlating the  

active column with when voltage is received on the  input row, we can determine the exact intersection  

of column and row and thus which key is pressed.  However, with this solution, we’re continuously  

scanning 3 volts across the columns, which takes  power thereby draining the batteries. So instead,  

we found that it’s more practical to have 3 volts  on each column, and when a key is pressed, a cycle  

of pulses of turning off one column at a time is  sent to determine which key in a row is pressed.  

These pulses are sent for 65 microseconds to each  column, once every 4 milliseconds. Therefore, if  

the G key were pressed, then the 3rd row would see  an input that looks like this. Whereas if the T,  

L, and A key were pressed, then the 2nd and 6th  row inputs would see a voltage that looks like  

this, and all the other rows would see nothing. Now that the microprocessor knows which keys are  

pressed, it sends the data to the 2.4 gigahertz  transceiver using these printed planar antennas. 

We’ll cover these antennas as well as the  oscillator in another video, but for now let’s  

close this inexpensive keyboard and look inside a  mechanical keyboard that costs over 50 times more. 

But before exploring mechanical keyboards,  the next portion of this video is sponsored  

by Keysight’s virtual event, Keysight World:  Live from the Lab. In this livestream, Keysight  

will be exploring batteries, DC to DC converters,  and a wide range of IoT devices through hands-on  

design analysis and Q and A sessions with industry  experts. Sign up quickly because the next Keysight  

Live event is May 16th, and by attending this live  stream you’ll be entered to win an oscilloscope  

in their test gear giveaway. In fact, the only way  we were able to reverse engineer this keyboard was  

with an oscilloscope just like this one, where  we could easily see the cycling of OFF pulses  

whenever a key is pressed. At Keysight’s upcoming  Live from the Lab event, you’ll learn many useful  

tools such as how temperature can affect battery  and device life as well as techniques and tricks  

for using DC to DC converters in your designs. Whether you’re an expert engineer or electronics  

newbie, there’ll be plenty of opportunities to  learn new things. Hurry up and register for the  

May 16th Keysight World livestream using  the Branch Education link, and you’ll get  

an extra entry into Keysight’s huge test gear  giveaway. Go check it out! But now let’s get  

back to the inside of this mechanical keyboard. Instead of seeing plastic sheets, we find a rather  

large, printed circuit board, with mechanical keys  soldered to it. This PCB functions similarly to  

the keyboard matrix, but now we have an LED under  each key to create attractive designs. However,  

quite noticeable with the mechanical keyboard  is that these keys have a different tactile feel  

and make a clicking sound when pressed. So, let’s look inside one of these keys where  

we find a keycap on top, the stem and slider  below that, a top and bottom switch housing,  

and inside are a spring and two metal  contacts which are also called metal  

contact leaves or gold crosspoint contacts. The main mechanism is that when you press a  

key down, it moves the stem and slider. The  slider is uniquely shaped such that it pushes  

one of the contacts away from the other, and, when  pressed down, the slider moves out of the way,  

allowing for one of the metal contacts to spring  outwards and hit the other, thus creating a  

connection between the two pieces of metal and  causing a click sound when they hit. When you  

release the key, the spring pushes the slider,  the stem, and key back up and the slider reengages  

the metal contact, thus separating the two metal  contacts and opening the connection between them. 

The stem and slider are separate components, so  that if you accidentally brush a key, the keycap  

and stem can travel a small distance down before  the slider is engaged. However, once the slider is  

pushed a frac-tion of a millimeter down, the metal  contact quickly forces the slider to jump out of  

the way allowing the metal contacts to engage. By having such a mechanism, each key has a more  

tactile feel when pressed, different from  the key hitting the rubber dome. That said,  

having a large PCB such as this, as well as an  intricate mechanism inside each key, causes this  

keyboard to be significantly more expensive, but  depending on your preferences, it can be worth it. 

Finally, there are laptop keyboards which  have a scissor switch mechanism along with  

rubber domes to allow it to have a lower  profile, but let’s wrap it up for now. 

This topic is moderately simple, but we think  it properly highlights the cost difference and  

engineering in two similar items. We’re working on  more videos that dive deeper into the engineering  

inside computer architecture and other complex  technologies, so be sure to subscribe, hit that  

like button, and share this video with others. We believe the future will require a strong  

emphasis on engineering education and we’re  thankful to all our Patreon and YouTube Membership  

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you can find the links in the description. This is Branch Education, and we create 3D  

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