I can confirm that this way of sensing velocity works perfectly fine. As mentioned high-end keyboards like the Roland D-50, Alpha Juno 2, JX 10, etc. used the same method as well. No need to make things more complicated than necessary

foam on speaker wires is porobably to stop them rattling against the case

Brilliant intro, *Sick beats Dave*

That double switch arrangement has been done for velocity sensitive keyboards since forever, the thing is, that this particular model is really really cheap and the piano sound on it is absolutely phenomenal for the price. (I play piano myself) A really high end keyboards have triple contacts and mechanical hammer arrangement for the keys. The hammer mechanism simulates the feel of a real piano and three switch arrangement allows the note to re-trigger even if the key isn't lifted off completely before re-engaged, like in a real piano can be played. Since in two switch arrangement you have to lift both contacts off the board before you can press the key again, the third just allows two of the three to be off the board earlier then full travel of the key. :) It's necessary for very fast and demanding piano pieces where there are repeated notes in quick succession and there's no time to let the mechanism lift the key completely before having to press it again.

I'm glad you did this particular tear down. I just ordered a CT-X700, now I don't have to fight the urge to take it apart to see how it works. As far as your piano skills you and I are on par. Thanks for the informative video.

That blue strip does most likely serve another purpose: The highest notes on a piano are always lighter (easier to press). I bet Casio emulates that by using a slightly softer rubber for the highest octave (12 keys).

Just to confirm what others have been saying. The dual membrane contacts are a music industry standard for velocity sensing keyboards and has been since the late 80's. As was also mentioned there is occasionally a pressure sensing strip on higher end boards for channel aftertouch. Basically the rule is, if it's cheap and it works don't screw with it. Generally these sorts of contacts have a functional lifespan of about 20 to 30 years or so. A common point of failure on older boards occurs when the suction of the silicone cups sucks dust and crud into the contacts causing either the key to fail outright or else the velocity sensor goes out of whack and the key always plays at full velocity. Simple fix usually entails removing the strips and cleaning the contacts with denatured alcohol. I'd love to see a board with optronic sensors instead of membrane contacts to address this problem but as you said. If they can save a nickel on a switch the cheaper solution always wins :P

Thanks Dave. More stuff like this, please!

There is indeed a musical term for that - we refer to the black keys on a piano as "black keys". Those carbon pad boards look very similar to the ones in my M-Audio keyboard. I would be shocked if I found a budget instrument with any other technology for the velocity thing.

Almost all synth keyboards use this type of velocity sensing. Some have additional pressure sensitive strip to provide shared aftertouch functionality. Some Ensoniq synths used inductive sensing to provide continuous per key position for polyphonic aftertouch in addition to initial velocity.

@ 16.30 those strips would be to hide the joins so you cannot see the pcb between the keys.

Thanks. Troubleshooting done by myself after seeing how it's safely opened up. Wonderful content mate.

Very informative. More videos like this showing how they get the price point down is a thumbs up from me.

Velocity only needs two digital signals. It just measures the time delay, and from this, you can get perfectly accurate velocity.

I have to say I enjoy your enthusiasm. Makes the video much better. And somehow you are remind me of my london born mailman. Always happy to chat.

Simple, but clever way to create velocity effect. I like it.

I enjoyed this simple teardown! Hopefully you get some more interesting keyboards to look into!

Very informative and interesting. Thanks for doing this teardown.

Nice change of pace (no pun intended!), it's good to see how they keep the cost down, such a simple mechanical solution...

The letters stamped into the backs of the keys you mentioned refer to the pitch name of the key. You were correct. The boards are also labeled to provide a guide for where each octave of keys goes (note the big "C3", "C4", "C5", and "C6" printed on the tops of the boards). As for the odd row of 13 blue keys at the end? That's for the top octave of the keyboard because a standard keyboard includes a final, 13th "C" key at the very end.

Thank you again. You are awesome.

This kind of construction with a pair of carbon contacts is actually the most common way of making a velocity sensitive keyboard mechanism, even in very expensive high-end instruments. It was also used widely back in the 80s - I own several different vintage synthesizers which use the exact same kind of mechanism (such as a 1986 Roland JX-10), and apart from a sturdier metal construction and a resistive aftertouch strip, it is exactly the same as this cheap Casio.

You are not the 8bit guy!!!

Glad I saw this vid. I’m a pianist and keyboardist, been playing for over 35 years now. I’ve owned many keyboards over the years. One of my current keyboards is Casio’s highest arranger workstation (MZ-X500). Casio has been using this keybed across their line for years now. It’s considered one of the lowest quality set of keys out there too. I’ve been wanting to take my very expensive Casio apart (which costs $1,100) to see how cheap the keys really are and your vid saved me the hassle. I’m shocked at how low the quality is on those keys! I know a lot of keyboard players that own Casio’s more pro oriented models that would love to see this vid just for the disassembly of the keys. We knew they were cheap, but damn!!!!!

About your question regarding the labeling inside the keys. I've had some piano-lessons as a kid and I still remember the basic octave-layout: C # D # E F # G # A # B the key-section you first took out provided the D, F and A keys, so the labeling simply identifies the notes they are meant for. (simply a case of better safe than sorry)

Casios are the best! If you run some on low voltage, you can get a kind of "circuit bending" effect on them. Random sounds playing when you press a key. Something to try. :) EDIT: I used to plug the audio output of my casio keyboard into a control for a radio-controlled car to broadcast music on both the AM and FM bands (on several broadcast harmonics). I could broadcast music to the whole house and even managed to pick it up on the television, albeit with very low reception.

And now, for your listening pleasure: the fantastical musical stylings of Dave!!!

As someone who didn't know what a scale was (or a musical Key for that matter) until quite a few decades in to his life, can strongly recommend that you take up the piano. It will help your brain as you age... learning new, complex skills that combine motor coordination, memory, etc. It's interesting how many benefits it has. It's given me a new appreciation for musicians and musical engineers. It also imposes a level of discipline and provides a reward system for that discipline that you often don't get in daily life.

Yup, that's pretty much how they all work. It just measures the difference in time between both carbon contacts being pressed. The most interesting pressure and position sensing devices are on much more expensive instruments like the Haken Continuum or the LinnStrument. Roger Linn talked about designing those pads during his interview on Embedded.fm podcast. www.embedded.fm/episodes/236

Excellent channel! Greetings from México

Very interesting how they measure the pressure (=velocity) on the keys. Thanks for sharing !

That was interesting, cheers Dave!

Masking so you can’t see the green PCB through the gaps between the keys. Should have used a black PCB, but probably costs more?

I love to find old Casio keyboards that people junk at the local consignment shops and circuit bend the hell out of them. The keyboards are junk, but circuit bending them at least makes them into something interesting and fun.

I have opened up a few keyboards in my time and I believe that the sponge strip on the back of the main panel is purely to reduce vibration against the case when it's being played.

I just picked one up the other day, for the quality of sounds the price is hard to beat.

That's some clever cost-cutting construction there. It won't sound great to a professional or hobbyist, but for someone who would just use it to practice piano (or for a children's piano lesson recital), this is pretty great.

Velocity sensitivity is done by timing the interval between the two contacts firing. Even the high-end keybeds do it this way. There are other ways, especially in older stuff, but this is definitely the way the majority are done today. Many older keybeds (80's, 90's) need the carbon replaced on those contacts. The more expensive keyboards let you adjust the timing curve between those to change the response of the keybed. Aftertouch (technically called channel pressure), which this doesn't do, is usually accomplished through a sensing strip that goes across the full length of the keybed. This is why the vast majority of keybeds only do *channel* pressure, meaning they apply the pressure to every key, vs individual or polyphonic expression. That limitation has gotten under enough people's skin that we recently voted to approve the MIDI Polyphonic Expression standard (MPE). Where did they save money? - Main thing is reuse across their product lines. - Keys are in octave units, so they can make the keybed as big or small as they want. Likely reused across many of their consumer keybeds - Printed carbon resistors for the board (because they already had to print carbon). - No springs on the keybed. They just used the plastic hinge effect. - No weights on the keys - No poly pressure on the keybed - No classic DIN MIDI input or output (saves a couple connectors, an opto-isolator, and a serial connection or two) - Surely reuse that logic board across a number of their keyboards - Cheap screen :) Other than any labor, the most expensive thing here that is specific to this one keyboard is the molding for the bottom of the body. I bet even the top is sectional so they can reuse the speaker moldings across bigger/smaller and only need to replace the center molding

If you want a real treat to teardown is a Yamaha CS80, analog core with a digital back end and only 800 units were made around the end of the 70s.

Well worth the look

I think if you look closely the rubber membrane is stepped, with the front contact being shorter than the rear one.

The alternating moldings for the white keys: to avoid adjacent keys sticking to one another when they're being molded?

I just realised, you could slide a thin double sided PCB between the battery and it's terminal for a meter to read the current consumption.

2 contacts for if you hit the note hard you get a lower volume so only the one that is not the same size, longer one touch and if you really hit the note hard than it's the other one that touch, shortest one, and the sound is than louder ( Louder input). Usually it's for that reason, i'm not saying that this is the case for this one but usually it is the reason why there are 2 of them different longer. Thank's for your very instructive videos Dave.

Didn't know you could play Schoenberg so well, really impressed.

For not working on key beds, you figured the workings very quick. Almost all keyboards use this kind of arrangement since the mid '80s. For aftertouch they typically use a force sensitive resistor strip that each key can make contact with which allows variable modulation control depending how hard you press down on any key AFTER you initially TOUCH it.

Dave, it is not about the angle of the key determining which contact is pressed first. If you look closely into the rubber molding, you will see that there are two pins, and they are of different length / depth. The longer one will make contact first with carbon tracks on a PCB, the shorter one will make a contact next. Casio (and their ASIC) knows geometry, and difference in heights of these pins, so can easily calculate absolute physical velocity of the key, and calibrate the rest, and do processing.

The plastics being done in sections will also be to reduce costs, they can then use smaller moulds (which are easier to make and tune) and can also run in smaller injection moulding machines. Also some parts could be used across different models, effectively reducing the cost even further.

start on 2:12 .... in one tone key there are two rubber contacts (1st and 2nd contacs). the distance between 1st and 2nd will be a logic (timing), the stronger you press is to faster the timings, and the voice will gets stronger

17:33 Had that same exact kind of construction on a 1993 Roland E-16, just different mouldings.

Very awesome Dave! Membrane keyboards are interesting to me. I've been sorta pretending to fix a MSFT keyboard (the control board is single sided and has a Cyprus controller chip), but I haven't because I'm a bit distracted by other things!

I've seen people press the black keys, too, and it makes it sound better.

Moulded channels on the undetside: That's a structural consideration. It "corrugates" the case for stiffness and provides two vertical walls to support the piano key fulcrums. If there weren't channels in the bottom of the case, there would have to have been either a single flimsy thin walled fulcrum bar or a separate moulded fulcrum part that may not have been as stiff as using the whole case.

Dave, if you look closely at the dual carbon contacts under each key, you should see that one contact is maybe a millimetre closer to the pcb than the other (shown at 17:19 on the video). That’s where the offset is, and the timing between them is how they track velocity. I’ve got an old Rhodes (Roland) 660 that I’m repairing at the moment, and that has an almost identical setup, and also has a membrane that senses all the key’s backstop position for aftertouch.

High expectations for US$280, Dave. These things are amazing examples of cost-reduction through industrial design. I didn’t realise that the two ‘sensors’ ;) were quite that close together, though. I would have thought that the variability from key to key would be quite high by having them so close together - my expectation was at least 15 mm between each. But I guess it is ‘good enough’, and reduces the cost a bit. The considerably more expensive ‘digital pianos’ have clever key designs, but they’re a huge PITA to disassemble. If this one gave you trouble and you decide to pull apart one of those, then maybe hand it off to David - ‘student job’. :D

The two-contact method has been used ever since velocity sensitivity came along, and it's used in every single keyboard because it simply works. No one bothers with distance sensors, that's just silly and expensive. They work exactly as you guessed, measuring the time difference. Actually, exactly the same thing is happening in electronic organs, just with a single contact because there's no need for velocity sensitivity there. The ASIC is most likely doing what everyone else's doing, especially at the cost, which is playing back old regular WAV files, recorded from a grand piano for each key separately and at 4 different velocities. They're then played back and crossfaded together for the intermediate velocities. There's also likely a DSP there for reverb.

Reminds me of the Casio CTK-4200 that I used to have a few years ago, it had similar features for the price

My first teardown of something like that was a Concertina I found at the local dump. My dad actually let me BRING something home from the dump. It had some sticky keys and I decided to try and fix it. The bellows were made of cardboard, tissue paper and cloth coverings. They used beeswax to hold things together. Sadly, I forgot and left it outside over night and it got rained on. I decided to leave it out all day in the hot summer sun to dry it. Well instead, the wax melted and everything fell apart. Apparently, the glue holding it together was water based becase it immediately began to fall to pieces as soon As I picked it up. Then the wax got hot and melted, causing it to stick together. The reeds inside fell out, the bellows un wrapped and the keys all fell off the board,and low and behold, all these tiny springs began jumping out from under the keys. This explained why the keys would stick and as soon as you worked the bellows. My parents actually bought the octagon shaped one for my sister for christmas a. I actually learned how to play it as it was much like playing my harmonica, without blowing into it. I got pretty good at playing it too. I sold it years ago now. I still have my harmonica and once in a while, haul it out and play it.

My guess is that all the bits of foam are needed to keep parts from buzzing when notes near their resonant frequency are played.

Same style of mechanism is used on the Yamaha DX7, one of the most popular professional synths of all time, even!

You should try and get hold of an M-Audio Axiom series midi controller (such as the Axiom 49), not only do the do velocity with their keys they also allow for after touch for vibrato. When you monitor the MIDI output they are constantly measuring the pressure on each key so you can change the volume of a synth on the fly or add extra effects as you add or remove pressure.

Time to watch the video. Wanna know if it uses dsp's haha. Thanks Dave for taking it apart! edit: got to the part when the board is shown my dissapointment is inmeasurable

I have a ctx700 and always wandered how it was inside. Thnks for your video.

The alphanumeric markings on the backs of the white (major) keys denote the note within the diatonic scale (A to G) and presumably the black (minor) keys have similar markings.

The bottom 3 sections are removable for cleaning, the keys will get sticky and dirt etc will get stuck under during use, take those off, clean the hair and dirt, just like new again! :D

The patron saint of teardowns does it again. Are subbing in for The 8 Bit Guy while he is on holiday?

I remember requesting a CASIO KEYBOARD TEARDOWN just a few weeks ago on *EEVblog #1102 - Casio FX730P 1980's BASIC Scientific Computer* and _YOU HAVE DELIVERED!!_ I feel like a celebrity now (well, not really) Any how, YOU ARE THE MAN!!

Probably been said a lot, but that's a pretty bog standard velocity detection system, and it tends to get the job done pretty well. Just as you had said, you just use the timing of the two presses to get a delta for your velocity.

very good !

I have a relatively high end stage piano that uses the same method to detect velocity.

When I saw the thumbnail, I thought it was 8-bit keys for a sec. You should check him out, Dave, but you'd probably like his main channel, the 8-bit guy even more.

That board looks EXACTLY the same as a cheap "non-brand" I repaired a few years ago. Unfortunately I forgot the name of that one, but looks like Casio also rebrand stuff or maybe they all use the same "datasheet schematic"

Foam maybe for buzz rattle control.

17:45 the stepped pads are visible on the carbon side - in the silicone mold one is shorter than the other. The key pressed both at the same time but they are different height. (Visible at 17:25)

17:25 - These looks like time-delayed carbon pads to detect the "velocity" of the keys. The faster you press the key, the less of a time delay there is between the first and second one making contact, so it produces a higher amplitude note.

Hey Dave ... not sure if you spotted it but the PCB of the volume pot looks like it was manufactured as a whole with the board; routed out and rat bites put in so they could easily snap it off and flip it over.

13:00 All low price keyboards use this kind of keys, I would like them to make the joints with steel strap, so they would never break. When a model becomes old, it may be impossible to get the matching keys.

Ohey, EEVKeys uploaded!

"Somebody had a little bit of fun" 🤣🤣🤣

I had a Casio CT650 that I bought at a local charity shop. cost £7.50. was a good keyboard.

Always enjoy electronic musical instrument teardowns. I've done a few myself. The velocity keyboard configuration is very common, and has been used for at least 30 years. I did a video on my channel repairing the keys on a Roland GAIA SH-01 synthesizer, and you'll see the same 2 carbon contact pads under each key. The interesting difference is the spring mechanism on the Casio is just using the plastic, as you point out may not be a long-life solution. The Roland keyboard I repaired had actual springs, and although it is also very "plasticy", it has a little bit more quality to it. Let me know if you want me to link it :)

I think that white silicone thing under the key is used to slow down key's up movement. Similarly as it is done in cassette deck.

From memory, the Sequential Prophet T8 has a fairly convoluted optical sensor setup for velocity sensing and polyphonic aftertouch. Quite a bit less attainable than a Casio consumer keyboard unfortunately.

Maybe they use the change in resistance from pressure on the pads too, at least as a hint

there may be some amplifier related problems with newer and even some older versions of the ym2612. A chip that was later integrated into an asic. If you have anything on the yamaha side (infinite instruments, but 90% sound like ringing or bass guitar.) it would be interesting to see if their asic has the signature over amplifying distortion compared to a working opl2 or 3 chip

Dave, quic trick - play only black keys. They always will sound right and you will look like you know what you're doing :P

Yes, very interesting.

I heard the keys had this time sense based on the 2 sensors. I think by definition, there must be a time where the first one is being still pushed in as the 2nd is moving. So I guess at least one of the switches has an elastic on state, that has to be durable. I've got an M-Audio 88es, a Casio LK230 66 key with an octave less, but it lights up when you play midi through it or play it, and a Casio CZ-101 with small keys. The CZ-101 is pretty useless but you can play a lot at the same time because the keys are so small. It has some nostalgia value because some early DM used it.

15:30 - Maybe those printed carbon resistors are for 'pedency-matching :) Now that I viewed the rest, I must agree with you, David! ;0

Are the blue ones easier to push down? They might have tried a grand piano weighting where the upper keys have a lighter touch.

Reminds me of that one time I had to Re-Carbon all those damned contacts on a Roland Juno D. All I had was graphite spray and some toothpicks. Good times :D

Looks quite like what I see on my Yamaha Clavinova (CLP-150), except for a more complex mechanic to mimit a piano key (they basically build the hammer mechanic but ignore the hammer and take the measurement as shown in the video). You mentioned the problem of getting the plastic right: Yamaha failed on the Clavinova in this regard, i.e. keys tend to break after a while and become sticky. You can buy replacements for 15€ each plus assembly, if you cannot to this yourself. So the plastic is a weak point, if not done right. However, after almost 20 years I only had to replace one key.

It looks like there's a hight difference between both contact? That would make it very easy do determine the speed of the keypress.

Do u have any idea how to add USB port and/or Pitch Bend on this keyboard? The only different beetween Casio ctx700 and ctx800 are ctx700 doesnt have Pitch band and USB port.. Can you do some modifications to add (at least) Pitch bend?

13:31 - "D", "F" and "A" refer to the notes they are. The "56" I'm not so sure about.

Did a quick browse of the comments, so couldn't find an explanation for the carbon resistors underneath the keys. I'm willing to bet that they are used for multi-level logic. You can push down as many keys as you like and the keyboard registers all of them, like a computer keyboard with n-key rollover. And yet there aren't 61 (with velocity, 122!) wires going from the keyboard to the processor, so resistors are used to divide the logic into multiple levels. I've seen this before myself, disassembling my car's steering wheel. All the buttons on the wheel are going back to the computer through one wire, with resistors on each to allow the computer to deduce which buttons are pressed.

So my prediction was a rubber pad striking a piezo strip, then the shape of the strike signal was then applied to the sample. I suppose this required infinitely less cost though.

I Have an EZ220 Casio which is a couple of year old model which i picked up broken for next to nothing and repaired by re-soldering a couple of bad joints. The construction of the key mechanism/velocity control etc is identical. The only real difference is the pannel section and the processor board. I guess they are making a huge saving by reusing already designed (and paid for) moulds etc. Actually not quite identical... in the EZ220 they still used connectors on the ends of the ribbon cables

Hi Dave I am curious. After tearing this CT-X700 down, did you assemble it again or went it straight to the garbage bin? I don’t like it when music instruments are getting brutalised.

That intro it was like Mozart Incarnate!