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henq
Joined: Nov 29, 2006 Posts: 23 Location: holland
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Posted: Sat Jan 27, 2007 4:14 am Post subject:
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hmm, my camera got broken and i still have to get a new one...
but i'll try to get some pics soon.
ill check all the switches, and maybe i can get them all to 190 ohm by soldering some resistors to them...
thanks for the reply. |
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Uncle Krunkus
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Joined: Jul 11, 2005 Posts: 4761 Location: Sydney, Australia
Audio files: 52
G2 patch files: 1
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Posted: Sat Jan 27, 2007 5:53 am Post subject:
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If there aren't resistors already in series with those switches, then there's something seriously wrong with them. A closed switch shouldn't read anymore than 2-3 ohms, (and that would be the resistance of the meter leads! ) _________________ What makes a space ours, is what we put there, and what we do there. |
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henq
Joined: Nov 29, 2006 Posts: 23 Location: holland
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Posted: Sat Jan 27, 2007 8:13 am Post subject:
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i just went out to get a new camera, as soon as the battery is charged, ill take some pics...
but i'm already guessing i had better chosen the matrix decoder thing...
anyway, if that is the case, i'm going to convert an old guitar into a single bus synth controller anyway, so i can still use the circuit.
i just opted for this one because i thought it would be easyer to make, and there was a stripboard layout for it and not for the matrix decoder (hint ) |
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blue hell
Site Admin
Joined: Apr 03, 2004 Posts: 24079 Location: The Netherlands, Enschede
Audio files: 278
G2 patch files: 320
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Posted: Sat Jan 27, 2007 9:10 am Post subject:
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Uncle Krunkus wrote: | If there aren't resistors already in series with those switches, then there's something seriously wrong with them. A closed switch shouldn't read anymore than 2-3 ohms, (and that would be the resistance of the meter leads! ) |
Don't know for sure, but maybe, when it has rubber contacts, the on resistance could be pretty shitty.
I don't know how the keyboard circuit is constructed, but when it's a resistor chain where the contacts just have to select a tap and give the voltage to a high impedance sample and hold a bad on resistance might not matter too much. (links we need more links here )
When the keyboard is set up in a matrix some serious trace hacking might be needed. _________________ Jan
also .. could someone please turn down the thermostat a bit.
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henq
Joined: Nov 29, 2006 Posts: 23 Location: holland
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henq
Joined: Nov 29, 2006 Posts: 23 Location: holland
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henq
Joined: Nov 29, 2006 Posts: 23 Location: holland
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Uncle Krunkus
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Joined: Jul 11, 2005 Posts: 4761 Location: Sydney, Australia
Audio files: 52
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Posted: Sat Jan 27, 2007 4:39 pm Post subject:
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Blue Hell wrote: | Don't know for sure, but maybe, when it has rubber contacts, the on resistance could be pretty shitty.
I don't know how the keyboard circuit is constructed, but when it's a resistor chain where the contacts just have to select a tap and give the voltage to a high impedance sample and hold a bad on resistance might not matter too much.)
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Now that I've seen it, I agree with Jan on both these points.
So,..... clear each switch from any outside connections, run a common connection to each switch, and loop a chain of 100R resistors across points which connect to the common. And,..... see what happens. If there's a problem, you may be able to increase the input impedance of the S&H, and the option of pulling it all off and trying the matrix solution is still there. _________________ What makes a space ours, is what we put there, and what we do there. |
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blue hell
Site Admin
Joined: Apr 03, 2004 Posts: 24079 Location: The Netherlands, Enschede
Audio files: 278
G2 patch files: 320
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Posted: Sat Jan 27, 2007 4:48 pm Post subject:
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Uncle Krunkus wrote: | Now that I've seen it, I agree with Jan on both these points. |
Me too _________________ Jan
also .. could someone please turn down the thermostat a bit.
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henq
Joined: Nov 29, 2006 Posts: 23 Location: holland
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Posted: Sun Jan 28, 2007 2:51 am Post subject:
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it was a 4 octave keyboard that i cut to be 3 ovtaves, so i'll try with the spare octave first...
but i think it could never be in tune, because the resistance of each button is different... |
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Uncle Krunkus
Moderator
Joined: Jul 11, 2005 Posts: 4761 Location: Sydney, Australia
Audio files: 52
G2 patch files: 1
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Posted: Sun Jan 28, 2007 4:40 am Post subject:
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Like Jan pointed out, if the input impedance of the S&H chip is sufficiently high, the voltage potential at that point of the resistor chain will be correctly carried across the resistance of the switch.
Trust us, we're doctors!
(Well,... Jan's a doctor, I'm just an inturn, but I do like chopping things up to see if I can put them back together.
"Uncle!...
Uncle!!....
I need another brain for my experiments!!"
"Yes master!......
I think I need one too!") _________________ What makes a space ours, is what we put there, and what we do there. |
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blue hell
Site Admin
Joined: Apr 03, 2004 Posts: 24079 Location: The Netherlands, Enschede
Audio files: 278
G2 patch files: 320
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Posted: Sun Jan 28, 2007 6:58 am Post subject:
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Uncle Krunkus wrote: | Trust us, we're doctors!
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OMG
_________________ Jan
also .. could someone please turn down the thermostat a bit.
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henq
Joined: Nov 29, 2006 Posts: 23 Location: holland
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Posted: Sun Jan 28, 2007 9:30 am Post subject:
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ill give it a go.
(first i have to get 2 more ICs in the mail, and find some time)
i wish i knew a bit more about impedance... |
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Uncle Krunkus
Moderator
Joined: Jul 11, 2005 Posts: 4761 Location: Sydney, Australia
Audio files: 52
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Posted: Sun Jan 28, 2007 4:22 pm Post subject:
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A bit of background info; -
Impedance is AC resistance. Sounds simple, but AC has many possible frequencies, and impedance is dependant on the frequency of the signal. So a certain component, or group of components, has an impedance of X ohms @ Y Hz. The same component will have a different impedance if you change the frequency of the signal across it.
Now, Jan and I are talking about the impedance of the Op-Amp in this circuit, because Op-Amps are often used for AC applications. In this situation however, the op-amp is buffering a DC voltage from the resistor chain. So it would be just as useful to speak of the op-amp's input resistance.
If it's relatively low (1K-5K), the resistance of the switch would effectively be part of a voltage divider, and would have a big impact on the buffered DC level coming out of the op-amp. If it is relatively high (5M-10M) then the 100 or so ohms of each switch will only have a tiny part of the signal dropped across them (.002%) and the rest will be accurately buffered by the op-amp.
Does that help? _________________ What makes a space ours, is what we put there, and what we do there. |
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henq
Joined: Nov 29, 2006 Posts: 23 Location: holland
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Posted: Sun Jan 28, 2007 10:09 pm Post subject:
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Uncle Krunkus wrote: | ...
Does that help? |
i think it does...
at least i understand it a little, i'm not sure if i can implement this knowledge, but tomorrow i think i'll have some time to look at the circuit again. |
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Ohmu
Joined: Jul 30, 2009 Posts: 11 Location: France
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Posted: Sun Aug 23, 2009 11:17 am Post subject:
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What kind of keyboard we have to use with the single bus? |
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Uncle Krunkus
Moderator
Joined: Jul 11, 2005 Posts: 4761 Location: Sydney, Australia
Audio files: 52
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Posted: Sun Aug 23, 2009 4:38 pm Post subject:
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A single bus keyboard!
In other words, there needs to be a common connection to all keys, (single bus) and each key needs another connection which is shorted to the common bus when pressed. _________________ What makes a space ours, is what we put there, and what we do there. |
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Ohmu
Joined: Jul 30, 2009 Posts: 11 Location: France
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Posted: Mon Aug 24, 2009 1:22 am Post subject:
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Thank for yout answer but is there a model/mark in particulary? |
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Uncle Krunkus
Moderator
Joined: Jul 11, 2005 Posts: 4761 Location: Sydney, Australia
Audio files: 52
G2 patch files: 1
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Posted: Mon Aug 24, 2009 6:08 am Post subject:
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Sorry, I don't know.
I made one with an old organ keyboard. _________________ What makes a space ours, is what we put there, and what we do there. |
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mikebike
Joined: Apr 06, 2010 Posts: 6 Location: MPLS
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Posted: Fri Apr 16, 2010 3:23 pm Post subject:
firtst post! |
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hey everyone!
long time lurker, firrst time poster
where is V+, V-, earth?
where do the key switches conect? the bus from the keyboard? |
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El Mop
Joined: Aug 20, 2012 Posts: 56 Location: Germany
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Posted: Tue Oct 02, 2012 11:21 am Post subject:
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I thought this layout had been made from this:
But since it doesn´t seem to fit and the fact that this post is from 2005,
maybe there had been something changed meanwhile?!
Anyway, can I anyone send me the right values for this layout?
Thank you
@mikebike
V+, V- and ground can be found on the left side in the middle (There are signs for +/- and ground).
There are two points in the layout labeled "Busbar" and "Ladder", where you connect the keyboard. |
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El Mop
Joined: Aug 20, 2012 Posts: 56 Location: Germany
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Posted: Thu Oct 04, 2012 6:48 am Post subject:
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The link didn´t work, now it does. |
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El Mop
Joined: Aug 20, 2012 Posts: 56 Location: Germany
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Posted: Sat Oct 06, 2012 5:22 am Post subject:
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Nobody knows anything about this?
Don´t believe it! |
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El Mop
Joined: Aug 20, 2012 Posts: 56 Location: Germany
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Posted: Thu Oct 11, 2012 1:59 am Post subject:
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If the schematic of this layout doesn´t exist and the even the creator of this layout doesn´t seem to know anything about it, this layout is pretty much useless, isn´t it? |
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El Mop
Joined: Aug 20, 2012 Posts: 56 Location: Germany
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Posted: Sat Nov 10, 2012 7:50 am Post subject:
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Found the schematic today by accident.
But by now it´s too late...
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