subtitle

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

eight critical parts inside essentially

removing all the components costs so

that you can buy them in bulk for as

little as

1.57 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

eight 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 four components are two

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 guide how do they work well the

main idea is that the batteries and

microprocessor apply three 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 three 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 sheets 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 unpressed 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 three volts along

each column while actively monitoring

the inputs along each row with this

reorganization you can more easily see

that as you press the y key three volts

is sent out along the fourth column and

returned along the second row and thus

the processor can tell that the y key

was pressed or with the b key three

volts is output along the eighth column

and input through the first row with 11

columns and 12 rows we can have a

maximum of 100 written 32 Keys which

works out well because the keyboard only

has 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 three volts

will return along a row however because

each of these columns output the same

three 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 three 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 three volts across

the columns which takes power thereby

draining the batteries so instead we

found that it's more practical to have

three volts on each column and when the

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

four milliseconds therefore if the G key

were pressed then the third row would

see an input that looks like this

whereas if the t l and a key were

pressed then the second and sixth 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

live stream keysight will be exploring

batteries DC to DC converters and a wide

range of iot devices through Hands-On

design analysis and Q 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

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 live stream using a

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 a 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

Cross Point 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 the key back up and

the slider re-engages 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 fraction 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 the

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 who 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

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