home brew switched MIDI guitar 8D

[nix808]

Hiya,
I have a construct which is only a thought, and may remain so.
I want to make a switched midi guitar controller
What I'm thinking of doing is taking 4.8 v AC, splitting it into 6 outs and running it down 24 * 6 microswitches on a guitar fretboard.
Each switch would have a different resistor, so there would be 24 different stepped amplitude values.
-additionally the microswitches would turn of all lower frets, so the signal is not confused.
these 6 lines would be plugged into a Presonus or M-Audio soundcard.
I would read peak amplitude on Flowstone PC software and create the MIDI notes.

What sort of signal is ideal for a soundcard's line in to read? ie. impedance, voltage, wattage, amperage fellas? -and is plugging a wall-wart into a soundcard problematic?
I would need to treat the signal to a degree yeah?

Hope you like my idea! It's just a thought atm

3 folks I thought I would like to bell are:
antto
BertKoor &
aciddose(who I talked to years ago 'bout it)
--if any of you would like to talk about the signal treatment needed and feasibility of the concept, that'd be real nice

I would construct the physical instrument, and do the signal processing in PC. Should I be able to get a nice/accurate division with resistors?

[BertKoor]

these 6 lines would be plugged into a Presonus or M-Audio soundcard.
I would read peak amplitude on Flowstone PC software and create the MIDI notes.

Why not use an Arduino to handle the logic going from hardware switches to midi notes? It's made for such things!
Would you rather risk to blow up a $15 Arduino or a $150 sound card (or a $1500 laptop's USB ports)

And you can use DC instead of AC controller signals.

What sort of signal is ideal for a soundcard's line in to read?

Alternating currents of around 1 volt.

If the signal is behaving like a line signal, that's like 600 Ω. That's like 1.667 mW. For a power supply that's nothing.

But look at it like this: your mains power coming out of the wall doesn't mind whether you plug in a washing machine consuming 1000 watts, or a LED lamp consuming 1 watt.

[antto]

i'm not familiar with guitars
but it looks pretty wasteful to me, to require 6 audio input channels for this thing, when the desired end result is MIDI
why not do all the required stuff as part of the "midi controller" instead? or if you still want a certain amount of flexibility (in the form of a plugin) then at least do as much on the controller side, and somehow "compress" the amount of data you need to transfer over to the plugin..

i don't understand your button/resistor scheme, i can't comment on that
it'd help if you could draw a picture like for 5-year-olds to understand

also note that many (most?) soundcards are AC coupled, so you can't rely on feeding DC signals into them
in fact, i didn't understand what kind of signal you want to feed into those 6 audio channels and how you're planning to use it

[nix808]

1:Why not use an Arduino to handle the logic going from hardware switches to midi notes?

2:Alternating currents of around 1 volt, 600 Ω. That's like 1.667 mW.

3:But look at it like this: your mains power coming out of the wall doesn't mind whether you plug in a washing machine consuming 1000 watts, or a LED lamp consuming 1 watt.

1: I would like to use a micro-controller/PLC to implement a 5-pin DIN MIDI port within the guitar, but I would need to learn to code for it. I am fluent in Flowstone as far as the required DSP.

2: Thanks a million Bert 8D I had no idea what resistance was right

3: Is this a problem? I would use a signal generator to start with I guess, but if hardly any current is drawn, hardly any current will be drawn?-- or will a line-in on soundcard draw a large wattage?

Cheers! I'll keep this thread posted with any development

Antto- I'll just do a drawing for us

oh- maybe I can use a RDSP board for this, using DC
--here's the board-> http://www.dsprobotics.com/flowboard.html

[nix808]

heya Antto,
I drew up a rough schematic of what I want to do->

MIDI guitar circuit72dpi.png

I have a great idea for it!
I will use a signal I create in FlowStone for the input oscillator/power supply
It can be like 5000 hz, so .2 ms
Depending on how the resistors step it, it could be do-able

--so the power supply is a soundcard line-out,
are you happy with this safety-wise Bert? it sounds fine to me

The hardware guitar would require a mono line-in,
so there mounted to it would be a 7-pin DIN jack output and a ts line-in
I would break out the 7-pin with a simple passive box placed near the soundcard

The DSP I would like to do is pretty simple, I will just read peak and that will be transferred to MIDI note. Also there would be a gate just above noise. The signal would be rectified, I guess it still needs an envelope follower of some sort hmm

[antto]

okay, i'm sorry but i should have made my question clearer
i already understood that you want to have some AC signal and some buttons with resistors, so the picture doesn't clear things up for me
i don't know much about guitars, nor anything about guitar midi controllers
what do the buttons do? are there strings on this? how do you want the signal to look like for different pitch notes.. how would the plugin tell what midi note(s) is pressed/released..?

[BertKoor]

Fully agree with Antto, do as much in hardware as possible. DSP makes it much more complex than needed. For all intents & purposes, you're building a (funky) midi keyboard controller,.

Don't ever ask me (or trust me on) what's safe.

240V surely hurts, but not often kills. Or I'd be dead 10 times at least. I solve ground loops by disconnecting the 3rd prong off all power plugs. While that actually makes sense (although illegal in some parts of the world) what does not make sense is I opened up my Arp Axxe and with a multimeter could trace where the envelope generator was about. Then I was curious what current was flowing. Switched the multimeter to Ampere, and that short-circuit (multimeter switched to Ampere has no resistance) was the end of a nice analog vintage synth.

On wikipedia you can find the definition of a line level signal. It stems from telephone lines. Low output impedance of 600 ohm goes into high input impedance of 10 k ohm.

Here's a calculator for stuff like that:
http://www.bertkoor.nl/VawoCalc.html
Or a bit more modern "app" :
http://www.bertkoor.nl/VawoCalc/index.html

[nix808]

1:what do the buttons do?
2:are there strings on this?
3:how do you want the signal to look like for different pitch notes.. how would the plugin tell what midi note(s) is pressed/released..?

8D
1:the buttons control the amplitude of the sine/triangle, thus giving me an amplitude step, which I read with DSP. I can discern which MIDI note it is by reading peak amplitude after 0 crossing. The resistors will affect the peak of the triangle, more resistance = less peak value
2: no, it will turn on the lines/strings with larger, soft, nice buttons
3: I think the best signal is a 5khz triangle, the signal will have different amplitude/volume for each of the 24 notes, to read it with the plugin or .exe, I'll rectify, then take peak after/later than 0 crossing

I'll reply in a sec Bert! 8D

[nix808]

how does this look fellas?

MIDI guitar circuit_0_1.png

the switches are 6 pin, 2 position momentary,
and cost around $1 each

how would the grounds work in your estimation?-- do I just need to connect them?
==> like input ground to output ground?