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 Forum index » DIY Hardware and Software » Circuit Bending
Matrix Keyboard/Trigger/Circuit Bending Question
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smmpcomposer



Joined: Oct 17, 2018
Posts: 7
Location: Brighton

PostPosted: Tue Mar 08, 2022 6:52 pm    Post subject: Matrix Keyboard/Trigger/Circuit Bending Question Reply with quote  Mark this post and the followings unread

Hi everyone,

I have been trying to think of ways to get a trigger signal from key presses on circuit bent machines, so that I could build simple EG to shape the sounds or the filters.

I know it's probably an easy and obvious question for many experienced people here. I am sure I have the answer in front of my eyes, and probaby it's a bit pointless since many sounds on those machines are already with a default envelope generator embedded. But I can't think of any easy way.

Is the easy way to go and use microcontrollers in order to scan and decode the keyboard matrix etc?

Someone built this amazing sytnh a while ago and uses Atmega8 microC.

Is it worth using lots of IC as in MFOS article?

http://musicfromouterspace.com/analogsynth_new/OLDIESBUTGOODIES/CONTROLLERS/scanningmatrixkeyboard2.html#

True that the try to get CV as well in there.

I have been circuit bending for a number of years, circuit bending and also trying to augment some cool keyboards such as the Yamaha PSS-80, nice little polyphonic beauty. Trying to get an EG working and in place is one of the things I have really been missing.

I would be realy grateful if someone could help, and if I built and do videos or post schematics I will obviously quote you in case, at the very least.

Thanks a lot and big hugs!

Samu
SMMP
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PHOBoS



Joined: Jan 14, 2010
Posts: 5591
Location: Moon Base
Audio files: 705

PostPosted: Wed Mar 09, 2022 2:09 pm    Post subject: Reply with quote  Mark this post and the followings unread

I don't know if it's easy but it should be possible.
btw I am assuming you don't just want to use the keys for something else but add it to the whole device.

With a scanning matrix keyboard you'd first have to figure out how it is scanning the keys. Does it send out signals
to the rows and read columns or the other way around ? does it use high or low level detection ie does it send out a
low signal for the row/column it wants to read or a high signal. Since it will be running at a very high frequency it's
probably not the easiest thing to figure out without a logic analyser or at least high frequency oscilloscope.
Though maybe using a binary divider (to lower the frequency) with a buffer/amp and speaker would make it possible
to detect.

Once you figured out how the matrix works it could be possible to tap into the signals and use them to create triggers.
For example if it sends out a high signal over the rows and then reads the columns you should be able to connect a
circuit to the columns to detect when a key is pressed. Basically doing the same as the CPU. Then you have to turn it
into suitable trigger signals which can get tricky.

Pressing a (single) key in the example above would result in high frequency pulses on one of the rows untill the key is released.
This doesn't really tell you which key is pressed but that shouldn't matter if you just want a trigger whenever a key is pressed.
If you use an SR-latch it is possible to turn these pulses into a single pulse. The tricky part is that you will have to reset this latch
when the key is released.

For this it might be possible to use a simple low pass filter and a comparator to create what is basically a gate signal.
This gate signal (or rather the inverse of it) can then be used to reset the latch when the key is released. The problem with this
method is that if you play multiple keys in succession without releasing them in between the 'gate' signal would stay high
and as a result you won't get any new triggers.


another way, which might be easier, is to use a micro processor that runs faster than the CPU of whatever device you want
to use and read the signals of both rows and columns and derive triggers from that.

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smmpcomposer



Joined: Oct 17, 2018
Posts: 7
Location: Brighton

PostPosted: Wed Mar 09, 2022 4:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey PHOBoS, thank you so much for replying, I appreciate it! Your name came across many of my google search ha! (love your Dronoscope btw..)

So, basically, if I understand right, the best and easier way is to use a microprocessor such as the AtMega8, which makes life easier anyway and will probably give better results..

I love the funky solution of using a binary divide to have a slow motion version of reality ha!

My purpose was to keep on using the keys as they were intended to, but to tap some kind of signal from key presses in order to then generate triggers for envelope generators (even if not perfect or clean, because of all the reasons you explained before). Besides, I guess that with circuit bending stuff, part of the charm is the lack of perfection (at least from my perspective).

I will have to deal with programming controllers which is somehow frightening...is it that complicated?

Thanks for your answer and your help PHOBoS, much appreciated!
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PHOBoS



Joined: Jan 14, 2010
Posts: 5591
Location: Moon Base
Audio files: 705

PostPosted: Sat Mar 12, 2022 4:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

Microprocessors are easier in the sense that it's easier to make adjustments and add functionality by just changing the code,
instead of having to add more components. And of course generally need less hardware to begin with.

Downside is that you have to deal with a limited processing speed (and memory) which can mess things up.
But if it is riunning fast enough it shouldn't be too hard to detect the signals and derive triggers from it.
also bugs, lot's of bugs often as a result of silly mistakes.

Though even with a microprocessor you will still have to figure out how the keys are wired and read.


If you've never programmed anything it can be quite daunting but if you go with an arduino and the arduino IDE
there is a lot of information available to help you get started.

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