Mysterious 'strip' found on keybeds of digital pianos - Page 1
Forum section: electronics / general

author: Yamin
author_rank: Frequent Contributor
timestamp: September 29, 2020, 07:31:33 pm
content: Hi guys, I have always wondered what the purpose of the mysterious strip found on the keybeds of digital pianos are. There seems to be a carbon line in the middle and soldered at both ends and in the middle. Doesn't seem to be connected to anything important :S and nothing is placed on top it when the keybed is assembled.Thanks in advance.

author: ajb
author_rank: Super Contributor
timestamp: September 29, 2020, 08:13:32 pm
content: Test strip to verify correct manufacturing? Measuring the resistance between those pads would verify that the carbon printing has bonded to the conductive tracks properly and that it's the appropriate thickness.

author: Yamin
author_rank: Frequent Contributor
timestamp: September 29, 2020, 08:31:54 pm
content: Thanks @ajb, so its a test strip? Do you happen to know any reference links online about these?Once again thanks for the help

author: floobydust
author_rank: Super Contributor
timestamp: September 29, 2020, 09:47:57 pm
content: Polyphonic aftertouch uses force-sensing resistance, those keyboards aren't just on/off switches.

author: Yamin
author_rank: Frequent Contributor
timestamp: September 30, 2020, 09:46:02 am
content: @floobydust the pressure sensor is underneath a red felt material and the keys touches that, but nothing touches these strips. The strips doesn't seem to connect to any signal lines. The schematic doesn't even show the strips.Thanks

author: tom66
author_rank: Super Contributor
timestamp: September 30, 2020, 10:03:24 am
content: I was under the impression that most music keyboards sense key pressure by precise timing between the two parts of the lever. If you hit the key harder, the time between the two contacts closing will be much shorter than a gentle press.

author: oPossum
author_rank: Super Contributor
timestamp: September 30, 2020, 10:07:30 am
content: That is velocity sensing. Pressure sensing occurs when the key is fully depressed and is used for aftertouch.

author: Yamin
author_rank: Frequent Contributor
timestamp: September 30, 2020, 10:08:58 am
content: Yep what oPossum said.

author: floobydust
author_rank: Super Contributor
timestamp: September 30, 2020, 06:46:22 pm
content: Quote from: Yamin on September 30, 2020, 09:46:02 amYou need to know if the resistive carbon-print is done properly, so I would guess it's test strip, as others have mentioned.Measuring the key-down switch resistance to determine pressure, I did see Roland use that for aftertouch sensing, although it didn't really work unless you really pushed down hard.

author: dnwheeler
author_rank: Regular Contributor
timestamp: September 30, 2020, 07:18:45 pm
content: It's also worth noting that most lower-priced keyboards (and most digital pianos - since real pianos don't have it) don't have aftertouch, and polyphonic (per-key) aftertouch is very rare.

author: Bud
author_rank: Super Contributor
timestamp: September 30, 2020, 07:32:04 pm
content: Can you measure the resistance value of the strip between the pads? May give some clues.

author: floobydust
author_rank: Super Contributor
timestamp: September 30, 2020, 08:12:31 pm
content: Aftertouch exists in piano mechanics, an entire lever system dedicated to it, from the felt getting squished. Very complicated.The hammer will hit and sit higher, I'll have to ask musicians how this translates into "expression" and why so important.

author: dnwheeler
author_rank: Regular Contributor
timestamp: October 01, 2020, 09:38:50 pm
content: Quote from: floobydust on September 30, 2020, 08:12:31 pmThat's a different kind of aftertouch. On electronic keyboards, aftertouch refers to being able to modulate the sound by changing the pressure on the key after the sound has started. On a piano, aftertouch refers to the mechanism that resets the key and doesn't modify the sound (the hammer is off the strings), though is can be felt and may influence how a player plays.