PIC Synthesiser??

[Jaicen_solo]

Maybe i'm crazy, but I was thinking today that it might be possible to use a PIC with some sort of frequency lookup table, connecting ground to the low E string, and using the Frets as switches, to create a bass synthesiser. Hs anybody here got any ideas if this is feasible???
I figured it would be possible with a simple 555 osc, with the frets as voltage dividers, but I figure the frequency would drift with temp/voltage. A lookup table will produce a fixed frequency all the time, so I guess that's preferable.

So, am I crazy, or would it work??

[pjwhite]

How were you thinking of triggering the sound?  Simple, but maybe not useful would be sounding your synthesized notes whenever the E string touches a fret.  (Also, if the bridge is metal and not insulated from the other strings, you may have trouble).  A possibly more useful method of triggering would be to have a pushbutton on the guitar that you can press to trigger the selected note.  Or, you could use a grounded metal pick...
As far as the sound generation, a PIC is probably not going to be powerful enough to generate complex waveforms -- you may have to stick with simple (digital) pulse waveforms.
Interesting idea, though.

[demonstar]

I've thought about this before too so I'd be very interested to hear how you get on if you decide to give it a go. I'm currently getting to grips with PICs in hope of making something similar to that so please keep us informed with how you get on.

Good Luck!

[Jaicen_solo]

I figured that the triggering would be easy. Since the strings are grounded, if  the frets are normally held high, touching to a string would give a low state, just like a synth key.
Obviously, that would only work for one string. If the strings were to be isolated, and the frets grounded, that would allow six note poly I guess.
Alternatively, if a bipolar supply was used, the low E could be -'ve and the A string +'ve.
Maybe it would be possible to split the frets into 6 conductors (all strings as ground). I'm not sure it's worth the engineering to make it work, but it would be a fun project!

[demonstar]

Could the wiring me run down the hole for the truss rod? I wouldn't imagine the strings would need much tension in them as they wouldn't have to vibrate. I'm sure I've seen a video of someone who'd made a guitar synth like you mention before. I'd be really good for playing rainbow style lead keyboard parts.   

I would trigger the sounds rather than just have it sound upon contact with frets. That way you can get a rhythm without having to hammer on with your fretting hand constantly. As a trigger for the picking hand you could have a IR beam between the bridge and base of neck (A phototransistor in bridge and a diode in end of neck).  When the beam is broken the by your picking action it would trigger the synth (Kind of like air guitar on the right hand). For that to work you would need to terminate the strings at the end of the neck (22 fret end) so that they aren't in the way of your picking action. That wouldn't be and issue as the strings aren't going to be picked or vibrate. So you'd have a bridge at the 22 fret where the strings are terminated and a bridge in normal position to hold the phototransistor. This is all sounding do-able and the PIC could easily control the triggering side of things and do some wacky stuff. Anyone fancy LED inlays flashing in time to the picking? Imagine that shredding.

You could have amplitude of the sound produced proportional to the amplitude of the picking action. Id imagine if you used a series of dioes and phottransistors you could maybe achieve this. How about pick with a magnetic pick and have some coils of wire in the guitar body. The faster you pick then the greater the induced emf so that could control the amplitude. Unfortunately I don't think neodymium picks are readily available in most local guitar stores. 

Okay... Okay... I gotta' stop dreaming. Anyone else see where I was coming from with the ideas (I know some of them such as the magnetic pick are silly but you never know). I think it'd be hard coming up with a method of detecting how hard the pick stroke is and relating it to the volume. Your making me want to try all this now! It's one of these things I will try when I get time.

[Jaicen_solo]

To be honest, if you were to make a monophonic synth triggered by a guitar, it is in theory pretty simple.
The frets and and strings can be set up to work like a keyboard matrix  with either low or high note priority (ie, 6x22 'switches'). The magnetic pickup output could then be fed to some sort of envelope detector, to provide some dynamic control; no sound produced till the pickup signal exceeds a set threshold for example. Some sort of rudimentary pitch detection could also be applied to allow for string bending as well, with some sort of dead-band before it's applied to avoid glitching.
Once this hardware is in place, it would be a trivial thing to produce a PIC based keyboard to MIDI design, so it wouldn't be limited to a dedicated synth. My guess is that such a system is well within the reach of a competent DIY'er. The circuitry is pretty simple (in theory), and the hardware would not be all that difficult to achieve if you have some experience with luthiery.
I also think that it would be a very playable instrument, since there'd be little to no trigger latency (assuming a fast MIDI device is used). I've seen complete PIC driven synths with latencies as low a 20uS (!), so that's not too big an isssue!! Check out MIDIBox.org to see what I mean.

[levon]

There was someone doing this exact thing over on midibox.org forums a while ago.

[snufkin]

and here is a pre built guitar ready to use
http://cgi.ebay.co.uk/Ultra-Rare-1970s-Ovation-Condor-Hammond-Synth-Guitar_W0QQitemZ220336510793QQcmdZViewItemQQptZUK_Musical_Instruments_Guitars_CV?hash=item220336510793&_trksid=p3286.c0.m14&_trkparms=72%3A1298%7C66%3A2%7C65%3A12%7C39%3A1%7C240%3A1318

it has split frets because it you to be paired with the organ generator from a guitar organ

EDIT actually I'm not sure this one has split frets but there are some that do

in the usa you can probably find one for a reasonable price

[Marc.yo]

i've been thinking about this and working on it with an IBM engineer. why not just use an AND gate/command for the sounding of the note. the signal comes from a piezo or electromagnetic bridge and it doesn't trigger until the AND gate recieves a signal from the string and the fret. ya got me?