monitor a guitar signal strength, then output a DC level?

[HankMcSpank]

Don't fall into the trap that a PIC is a panacea for all your problems... half the forum thinks that way and then they discover after a lot of wasted time and effort these little things sometimes need external help to accomplish some tasks - and multi-channel complex signal processing is one of them.

0603 size Resistors and Diodes are still very much hand solderable with a pair of tweezers and a steady hand. You quickly tack one end with a soldering iron so it anchors, solder the other end properly, then go back and solder the first end properly. If you're building a one-off it won't matter. Trust me, you WILL need to rectify and filter those inputs. You are going to waste a shed-load of time and effort and end up with mediocre results going down the route you plan.

The final output from the Guitar to the Amp is a sum of the individual strings anyway. You can always build an external 'in-line' box which has the added advantage that it can be fitted to any Guitar without voiding manufacturers warranties etc. If you do it using Thermionic Valves (a single ECC83 or any twin-triode equivallent will make an eminent AGC and pre-amp) you will have a queue of people breaking your door down to get one (since valves and stage gear are very much in vogue).

Just seen your reply (before I made my posting immediately above).

This PIC circuit is not for a guitar output...but for a guitar sustainer (ie feed the guitar signal back into a circuit which drives a coild to keep the string virating ...there's no combining any output here...the normal (mono) guitar signal still goes to the amp as normal. The only combining would possibly of a hex pickup into my circui to feed a sustainer driver coil.

The reason I initially want handle 'six' strings, is becuase there are quite a few guitar variants out there that have hex pickups (one pickup per string), but like I say, I can sume these & then treat them as one. The sustainer needs an AGC, a threshold, a limit & an attack/release 'user definable' input parameters...this makes a PIC ideal.

I don't think a PIC is a panacea...but in this instance it could be very useful - what I don't have any knowledge about - is how hard they can be pushed. For example is carrying out AtoD every 20us for 13ms, then repeating again in 130ms afterwards that onerous for a PIC?

I'm assuming not, as I'm only talking about 32 samples at 1.4khz for 13ms on one input pin ...then repeating every 130ms (& I can't imagine Microchip would have been able to call its converters 'AtoD converters' if they struggle at this relatively low sample rate & base frequency!)

[Melanie]

Read the DATASHEET for your PIC... especially the ADC section.

Instruction Cycle is FOsc/4 so a 4MHz chip has 1uS Instruction Cycles.

It will probably take you 60uS to do ONE ADC (aquisition plus external housekeeping, retrieval, storage etc). Your worst case scenario is 1.4kHz... that means one complete sine-wave in 714uS... you'll be lucky to do six acquisitions per half wave... if you're lucky you'll hit peak, if you're unlucky your best shot will have missed peak by 15 Degrees. So doing my Nostradamus bit and predicting the future, you'll have a resultant randomly waving about like a pr**k in distress by upto 15 degrees of Sinus.

Oh... and you know you're talking about not having any (or minimal) external components... unless your input has a DC bias (more components needed), half your input will be negative going... so for 357uS out of the 714uS the PIC isn't going to see anything, but worse, it's internal protection circuitry on it's pins may well load and distort your input signal during the negative half-cycle, so unless the signal is buffered (more components), you'll distort the output of your Guitar by the simple act of connecting up.

But don't let me put a damper on things... it's your life...

[Jerson]

I'm sure this is best done in discrete analog. Doing what you want with a PIC and the way you want is going to be a tough one. But as Melanie said, you have to make that call.

[HankMcSpank]

I'm sure this is best done in discrete analog. Doing what you want with a PIC and the way you want is going to be a tough one. But as Melanie said, you have to make that call.

Ok, after sleeping on this...you're right (& there's little point asking for advice, if you're not going to heed it from those that know!).

Many thanks for taking time to respond.

rgds,
Hank.