Thanks for a fast response guys!

I verified that a 5 pin midi cable is only 5 conductors, and I believe the middle conductor (2) is the bare wire that touches the foil shield on the inside of the cable.
5 wires plus a 6th bare wire that touches the foil would have been nice (the bare wire would connect to the plug shell on either end of the cable).

In the schematic I linked above, pin 4 is a hot signal, and pin 5 is switched to ground at the Midi message's values.
If I were to combine in and out in a single cable, I think I can do 3 pin Midi instead of 4. Basically, making in and out share a 5v line, and the two message lines will switch a transistor. Then I have two more pins for + and - power.

Seem doable? Or am I missing something?

-Matt

EDIT:
I think I figured it out. On the master (processor) pin 1 add: 5v or 9v to power other stuff in the slave (pedal), pin 2 remain: ground, pin 3 add: Midi out, pin 4 remain: Midi in 5v line that can share with the 5v line for Midi out on the slave, pin 5 remain: Midi out (signal).
That way it is still backwards compatible with regular two cable midi devices. I was planning to add this to the Midi in on the master, and Midi out on the slave, so I don't have to drill more holes.

EDIT 2:
In the first schematic I linked to:
http://www.tigoe.com/pcomp/img/midi-schem.jpg
Could pin 4 on both the Midi in and out ports on the same device, be connected together? It would still be the 5v+ -> 220Ω(out port) -> 220Ω(in port) -> Midi goodies; instead of the 5v from the other device plugged into this one, couldn't the power just be ported accross both pin 4's without damaging it? What is the point of isolating the 5v supplies between two devices like this?

Hello,

I just picked up an old A.R.T. X-15 Midi controller and an SGX2000E (already got an awesome Savatage tone out of it in the two days I've had it!), and of course, I must modify it.
The Midi controller is a pedalboard style, and it has Midi in, out, and thru. Also, it has a power port. (duh)

Now, my goal is to fit Midi in, out, and power onto a regular 5 pin midi cable so I can wire the X-15 to the processor with one wire, instead of 3. I don't want to use a 7 pin cable, otherwise I will need backups of those, whereas all my other Midi stuff uses 5 pin cables.

http://www.tigoe.com/pcomp/img/midi-schem.jpg

I was looking at this general schematic for Midi, and I noticed that there is a (source?) and a (sink?) for the input, and the output looks like a single line and a 5v+ output.
I'm assuming it's sort of a remote switching mechanism?
Could someone tell me if I could wire the 5 pin cord to be setup as Midi input, output, + and - power, summing up to 4 pins used, then having an Arduino on either end to do the "switching" that I stated above, whilst providing power to the pedalboard? Or is the Midi input a Clock & Data style setup? If its the first, then I suppose I'm basically doing uart at the Midi baud-rate.

One other question, the 5 pin midi cord, is it actually 5 conductors, or is it 6 (5 isolated wires and a bare wire touching the shielded foil) ?
I would assume it is the latter, and that would be why a lot of devices have the ground lift if their chassis is made of metal. But you know what they say when you assume..

Thanks!
-Matt

Thanks for the input.

I considered running another cable alongside the guitar's cable, which would be easily doable. However, if said cable ever crapped out while playing live, the most common cable on hand is a mono 1/4 cable. I suppose building my own cable would be the simplest.

I could do the fm thing, as long as its above 20khz honestly. 2.4ghz was just more readily available.
Given the circumstance (guitar cables defeat 1+ ghz), if I used a stereo guitar cable, I could have power over the cable instead of only onboard battery power, but could I use that as a two way communication line as well? For instance, on the left channel (tip) would be audio, on the right channel (ring) would be power to the arduino, and communication to and from the pedalboard.

As long as it wouldn't be heard or interfere with the audio signal, would provide reliable power and communication, would this be doable without building a proprietary cable?
It would be nice to be backwards compatible with a regular mono 1/4" cable when I choose to play it like a regular guitar, so I would be limited to using a 1/4" mono or stereo.
Also, I am going for a sleek look on the guitar, so having multiple ports for different scenarios is not my preference.

-Matt

Mike, thank you for answering my question.

Do you know of a better module than to use the NRF24 in this circuit?

I basically wanted a >1ghz fm communication line that wasn't going to cost me an arm and a leg, would work for a good distance(the farther the better), and would work over the guitar cable rather than through the air.
I was only thinking to use the NRF's because I have a few of them lying around, and they are really cheap in price, good distance, etc.

-Matt

EDIT:

I understand the NRF24 does not transmit an analog signal. A DAC/ADC combo would be necessary for that.

The attached picture shows the diagram.

In the future I plan to make a 2-way wireless guitar adapter. 2-way is necessary for guitar's and pedalboard's arduinos to communicate, while still passing the analog signal.
This would need to be backwards compatible with a regular guitar cable, and work on any guitar.

My idea for the wireless guitar thingy: (any)guitar->ADC->NRF24->air->NRF24->DAC->amp/pedals/whatever.
So with the NRF equipped guitars, it would be: arduino-->nrf24->(in parallel with guitar signal)->guitar cable->pedalboard->(splits to nrf24->arduino and guitar signal->pedals).
In this case, with the 'wireless guitar thingy', I could directly swap out the guitar cable with it.

I cannot have the nrf24's go through the air, it must be through the guitar cable. (will have no interference if I turn and am between the two nrf24s, physical objects in between the two will not affect performance, better asthetics, not having a 4 inch antenna sticking out of my guitar and having 2 of them when I go full wireless, etc.)
Overall, its better for it to be hidden and operate on a specific line, rather than the airwaves.

Does this make sense?
If the signal goes through the guitar cable, there will not be anything in the way of the transmitted signal, and there won't be outside interference due to the cable's shielding.

Sorry for the confusion.

So, my main question: will a very very low voltage AC signal hurt the nrf24s? I would assume not, since it is well below its operating voltage (even if its AC).

-Matt

Hi,

First, I have a few of these:
http://www.exp-tech.de/images/product_images/original_images/b9e551faebe0bf1227bc08d1b19f285e.image.550x550.jpg

http://www.emartee.com/Images/websites/emartee.com/RF24013.jpg

My question, is I plan to put one of these in my guitar, and one in my pedalboard. So the voltage will be +/- 1VAC.
Will there be an issue with having the antenna directly attached to either of the AC wires?
Meaning, will an AC voltage that low mess up the NRF24L01+?

I have considered using diodes to prevent flow to the antenna, but wouldn't that make it so neither chip could listen, only speak?

I think the audio signal would be fine, considering the nordic chip communicates at 2.4 ghz and would be far out of the range of human hearing. I will also put a filter for above 1ghz to save my pedalboard and amp.

Thanks!
-Matt

I see what you mean. Better to have tried and failed than to have wondered what if. 

I think I may default to using a stereo cable instead of mono. I'm trying to make something that would be easy to incorporate into guitars without much circuitry. Thought I'd try if it would just be something simple like a cap in line, you know?

But as for the stereo cable, I just need to make a sensing circuit for the pedalboard so it will stop supplying 9v power to the 2nd lead on the cable if a mono is plugged in. In this way, if the 1/4" stereo plug is used with a mono cable, the 2nd lug will connect to ground. I haven't decided on which method I may use: Use arduino to sense current, resistance, or voltage(I think voltage may be the easiest), or to just use a relay that will switch itself given the ground signal returns 9v, and then it will sustain itself there, then when powered off it will reset itself, or along the lines of that..
Can't really think of much else than that.
But if I used the arduino's analog input to determine the voltage(with a voltage divider of course), would the AC signal hurt the input if only for a short moment? I would like to not use an inductor if possible, unwanted distortion and low freq. loss through the arduino to ground.

But onto the communication/wireless. I picked up 4 nrf24l01+'s on ebay for <$8, so my evil idea is to communicate the ardy's with a pair(1 on pedalboard, 1 on guitar) and then transmit that directly on the audio wire rather than air. I just wonder, from the theory you have taught me thus far, I could run the 2.4ghz signal over the audio lines and the +9v line, without issue, right? Or would I be better off running it on the ground line?

Now for the possibly crazy idea. For wireless, run that into another pair of nrf24l01+'s, but with an antenna. I don't know how I would go about amplifying that signal just yet though. Off to google I go!

I had an idea to do something similar before. My goal was to be able to swap guitar pedal order digitally.

I think you may have a good combination, however the max4549 is a triple 3x2 setup, which may be overkill depending on how many things you have hooked up. Converting the audio signal to digital before the crosspoint switch, and then back to analog afterwards *sounds* doable. I haven't tried it though, as I abandoned my idea(my pedals decided they only liked a specific order).

I'd say one thing to be sure of is most chips won't like a negative AC voltage, and a guitar (pedal) can sometimes have a swing > 0.3 to 0.3v. Just bias the signal to bring it into a positive area to work with. The datasheet for the max4549 says it has internal voltage dividers for a bias.

Your ADC/DAC combo has a different input and output quality, but both are more than enough to achieve good audio quality. Depending on the signal you are throwing through this, you may only require something much lower quality. Unless you can find the chip for cheap, and find a DIP version or can solder SMD chips well, reconsidering is also an option.

Some things to consider. Good luck!

p.s. you can type [ url ] (your url here) [ /url ] but without the spaces in the "[]" areas, to give a hyperlink to the webpage, or click the 2nd row, 3rd from the left button (under the underline button), rather than having to copy/paste to open it.

As of yet, a few things I have discovered.

1. The power supply was the culprit in disabling all audio signal. (It also powers my processor/preamp)
Not sure theoretically how an AC audio signal would cancel the digital signal through the processor's power(maybe inverted phase cancellation?)
I had to run a separate power supply to get it to work.

2. I have only been able to get any sound with ceramic disc caps. I've tried electrolytic caps back to back(+ - +), metal film caps, and polyester film caps.

3. The more resistance, the stronger the signal is. (Because its a bigger load?)

4. The capacitance didn't seem to change sound level. I used as small as a 1nf, and as much as 0.5uf with no noticable difference.

5. Multiple caps in series seemed to increase the sound level just barely. While multiple in parallel greatly decreased it.

As for the variable resistor, it seemed to not make a difference. And the RLC method is for a low pass filter isn't it? I could try an LC method, but not sure how I would incorporate the resistance. Also, I've read places that a guitar's pickup is basically an inductor in series with a cap and resistor in parallel(RLC)

The op-amp circuit you describe.. by which you mean as a buffer to keep a specific resistance? That may be a good idea to try out, but would be sensitive to different pedal layouts(different IO impedance).

There also seems to not be any 20hz high pass filters available in a small package. I found this schematic however:
http://www.eeweb.com/blog/circuit_projects/20hz-to-200hz-variable-high-pass-filter
May be useable, but the schematic states 15v input voltage, and the tl072 is rated ±15v.
Could I just swap for a lower voltage chip, or just run this with 9v?

Thanks for the help Far-seeker, you have really helped me out so far.

My circuit so far:

EDIT:
https://www.dropbox.com/s/x4vxufqmuqc145b/ArdyForum1.bmp
The insert image thing didn't work.

But the minimum load can be as low as a few hundrew ohms (volume control) or less.
The new guitar I am installing this into(hopefully) will have selective bypass resistance which will cut out of the pickups.
I forgot to include that info originally, since I was testing it on my currently built guitar.

As for the diagram, it will look like I'm adding pointless DC power to the signal. I just decided to leave out the rest of the circuit (guitar-side arduino) for simplicities sake; its a proof of concept. I just need a 9v DC supply between the two capacitors, basically.

Honestly it shouldn't be over your head.  It's true deriving the the RC time constant formula involves calculus.  However using it to get a capacitor value in this case only requires solving for a single unknown using algebra. This is only 7th or 8th grade math, and you've demonstrated a grasp of mathematical concepts at least as, if not more, difficult in this thread.

I never took calculus nor have I seen that equation before, so I didn't have any background info on what was what. (I'm still new to AC concepts and combining them with DC and whatnot). Thats what I meant by over my head. lol

DC is basically zero frequency, but the confusion is really my fault.  I'm an EE that doesn't work with audio much.  Off hand, I do know that the range of human hearing is kilohertz in magnitude, but I didn't double check the exact range.  So for my example in an effort to get something that would yield some fairly easy numbers, I ended up choosing a frequency for the high pass filter that would actually exclude the entire audiable range for most human beings. smiley-red  The math is still sound, but you probably want to try something around 20 Hz , 0.05 seconds, instead.

The corrected example:
τ = R * C
τ = 0.05 s (20 Hz, inverted)
R = 8000 Ω (lowest possible load is the worst case)
Solve for C

C = 0.05 s / 8000 Ω = 6.25 μF

Ah, that will be of much help. I picked up a few caps from radioshack(way overpriced, if not for my discount) and I will give them a try tonight.

It's my understanding that we were discussing overlaying AC on the DC power, not on any of the wires going directly I/O (should never be done because the Arduino microprocessors can only withstand about -0.5 V on these pins).  If that is correct, the communication between the Arduinos will be on another wire or using wireless radio.  Therefore, barring electromagnetic interference (which can be mitigated if it occurs), this AC signal shouldn't affect the Arduino serial communication by either means.

That is correct, I will isolate the Arduino IO pins from any AC signal. The onboard ardy is going to control each pickup's(what I call presence: fades between full series to a ratio of series/parallel/bypass then to a bypass state.) and will also control the LEDs on it(vine fretboard hollowed out and has RGB LEDs in it; should look good I think). The mcu will only share a communication and power line with the actual guitar's signal.

One thing though I hadn't thought of earlier. FM signals, dependent of amplification power, potential distance will vary. But if its through a shielded wire directly to a reciever, would there be such a distance factor? Or is a 'typically' low distance longer than about 30~ feet?


EDIT:
I tried with a few different size caps, and the dc signal still cuts out any sound. I even tried up to 300uf in caps both parallel and series. The only thing that would make sound is when I would have atleast 200uf and be connecting another cap. When the leads would touch it would make a sound kind of like plugging in a guitar. So I think I may be getting closer, but how much higher would I need to go? Or is there another aspect I may be missing?

Yea, I would figure there would be no humanly-noticeable difference. But I guess it came down to myself being a tone-whore. haha
The last thing I want is for it to sound worse than it does now with just a cable.
My own ears seem to be more sensitive to higher frequencies than most other people it seems, so I tend to like a lot of high end freq.

It sounds more "open" to me; would the bit depth/sample rate make so little of a difference in the amount of headroom it has?(not only the sound quality)

But I could care less about any thing altering the sound out of the audible range. As long as it doesn't alter the communication.
My goal is to have the guitar signal within audible range(20hz to 20khz right?), then block between 20khz and my Guitar-to-pedalboard Serial freq, block between that and the Pedalboard-to-guitar frequency, then isolate those from the DC.

If this is the case, I may be able to lower the required audio quality in my ADC/DAC combo and it may be easier to create.

Thanks Brandon!

I don't have a scope unfortunately. And I tried that, but it did the same thing. I think I just can't find the right cap/resistor combination.
On my breadboard I had it like this:
To pedaboard, Cap leg with resistor to ground, Cap leg to DC power, DC power, DC power to Cap leg, Cap leg w/ resistor to ground, to guitar;
and of course common ground between the AC signal and DC power. I tried with smaller caps, but it would just cut out sound, and larger caps in parallel let more sound through, but as soon as DC was applied there was no sound at all, minus an oscillating whine.

I have been considering other cables. *sigh* I have so many mono 1/4 cables as backup, I'd hate to have to switch to another type.
As for a midi cable, that is a good idea; but the music I play, we tend to not have any use for midi..(YET! until I build a midi tracker for my guitar, but thats another story).
I have considered using a Stereo 1/4 cable. On the tip would be the guitar's signal, ring would have the ground, and the shield would have power.
I would swap the ground and power only if it wouldn't make it sound horrible. And all I would need is a short sensing circuit on my pedalboard, basically measuring the resistance between the DC and ground. The arduino would do a test on startup and make sure the resistance is >100 ohms, then enable the DC power. So it could sense a mono cable plugged in instead, and automatically disable the power.
But then I'd have to buy some Stereo cables, and they may be less common on stage.

The math for this is fairly simple,

This is the math:
  |
  V _________
---/  d(0.0)b   \--->
            ^
Right over my head.. ha
How would I know which frequency to drown out for the AC? I may be wrong, but I though DC was a low frequency.

τ = R * C
τ = 5*10-5 s (I got this by inverting 20 kHz, your target value could be different)
R = 8000 Ω (lowest possible load is the worst case)
Solve for C

C = 5*10-5 s / 8000 Ω = 6.25 nF

How did you invert 20khz into 5*10^-5 ?
And to what scale would I use the resistor to ground the cap?
Since it would be a cutoff for (above?) 20khz, would that alter all sound above it? (fm frequencies for communication between arduinos)

Thanks for your patience, I appreciate it!

For the AC over DC, that makes me feel better about whether or not it would fry my arduino. The only thing though, I was unable to effectively do capacitive coupling for the guitar's signal. When I would apply the DC to it, it would just stop any sound. I was using a small cap (don't have any 1 farad non-polarized lying around) so that may be the issue, but if not, have I then done something wrong?

I would prefer to utilize a single mono cable (They are easy to come by, and if anything happens on stage I can easily swap it out; To make it backwards compatible without adding a proprietary jack beside the 1/4"; I don't want to use a Stereo 1/4" because I worry a roadie would put a mono in by accident and it would short my 9v to ground/I would have to add short circuit sensing circuitry to my pedalboard, which I find overkill if there is a better solution to just using a mono cable).
And I would go for the Due, only I would need 16 bit ADC and DAC at a minimum and would preferably use a 24 bit set, and space is an issue. I would need a Due the size of the Nano or Pro Mini to fit in the guitar. I could use it as my pedal board's processor though. I will look into that, thanks!

Current question: what would be the correct value cap to use for a 9v powered system(I may use diodes to half/full rectify the signal to stay at about 10v then regulate it before the arduino, or figure something out), that also has a min resistance of 8k ohms, max of 25k ohms?

In response to the AC blocking for the DC power to the arduino, this post has given me insight:

http://arduino.cc/forum/index.php?topic=124522.0

The act of converting AC into DC is called rectification.

There are two basic types of rectification: full wave, and half wave.

Full wave rectification takes 4 diodes and flips the lower half of an AC waveform upside down and superimposes it over the upper half:



Half wave rectification only uses 1 diode, and effectively cuts off the lower half of the waveform:



The Arduino has a single diode in-line with the power input jack to protect the system against reverse polarity connections.  This diode acts like a half wave rectifier.

A capacitor after a rectifier smooths off the peaks and troughs of the waveform:



If the ripple voltage remains above the minimum level of the voltage regulator, then all will be well.  The ripple voltage, however, is a function of the current drawn - the more current you draw the faster the capacitor will discharge and the more ripple you will get.

You will be fine running with an AC adaptor at low currents, but there will be a cut-off level where you will start to get glitches and voltage drops on the 5V line when you draw too much current.

So my question is, is that will I need to bias the guitar's AC signal into a positive AC signal instead of a +/- 0-1v or should that not matter? It will be sharing a 9V DC line, so it will still have power, I just don't want the guitar's AC signal to mess up my arduino.