Use LM3915 to meter Freq. i.s.o. Volts, Is it possible ??

[arma61]

Hi I mean is it possible to let the Leds connected to the LM 3915 move based on the frequence of the audio signal (I'm thinking specially about wahwah) instead of moving at the voltage increase/decrease ?

[Mark Hammer]

Yes, but you would need to do a frequency to voltage conversion first.  Not impossible, but the entire circuit (F-V convertor and LM3915 meter/display) would likely be more complex than the audio circuit being monitored.  If that is not an obstacle, then you're in good shape.

[arma61]

Thanks Mark for your reply, that conversion would be an obstacle for me as my electronic skills are very low. is there anything else you can suggest ? I'm building a "multi FX board" with ( 4 separate circuits) DOD250, Octave up sick box, an autoWah ( I cannot remember where it cames from I found it in the loft!), and a M3 Minisynth clone, so what I would like to have is a LED bar moving somewhere on the cover of the board, more or less according to the sound played.
Keep diying.

[Mark Hammer]

Do you simply want the bar-graph for effect or do you need it to provide you with user-critical information?  The difference between the two will help determine what direction to point you in.

[arma61]

yes just a bar-graph moving for a "light effect" (the other 4 Led, one for each effect, are multicolor RGB LEDs!!) no information needed, so just for fun and aesthetic!!

[Mark Hammer]

Ah, well in that case, you can use the "colour organ" approach, just like we used to do back in the day.

http://www.discovercircuits.com/C/color-org.htm
http://www.electronicpeasant.com/projects/ledlamps/ledcolor.html

Then, we used lightbulbs and solid-state control of varying AC sources.  Nowadays, we can do it with less hazard and lower current requirements using LEDs.  A nice selection of superbrights will get you a pleasing display that can be easily seen even though it's small.

The most straightforward thing is to take a feed from the guitar and send it to an active splitter of however many bands you want.  The splitter outputs each go to bandpass filters covering whatever ranges you want, and the filter outputs go to envelope followers.  The envelope followers, in turn, drive arrays of LEDs.  The brightness of each group of LEDs would vary with how much frequency content there is in that passband.  In theory, white noise would get you equal illumination in all LEDs.

You will note that this is not at all unlike a real-time spectrum analyzer circuit that shows intensity by frequency band, using LEDs.  There are probably old projects for them in ETI, PE, Elektor, Nuts and Volts, and the like posted around.  Certainly there was no shortage of related projects during the "golden age".

If you had enough bands, and arranged them in order of passband/frequency, it would behave like a "frequency meter".

[arma61]

The most straightforward thing is to take a feed from the guitar and send it to an active splitter of however many bands you want.  The splitter outputs each go to bandpass filters covering whatever ranges you want, and the filter outputs go to envelope followers.  The envelope followers, in turn, drive arrays of LEDs.  The brightness of each group of LEDs would vary with how much frequency content there is in that passband.  In theory, white noise would get you equal illumination in all LEDs.

thx Mark, but, unfortunately I'm lost in there, as I said before my skill in this matter is very low, I'm able to create a pcb layout from a schematic and etch, choose component and solder them, but that's all!, so when you talk about splitter, envelope followers I know almost what you're talking about but I don't have a clue where to start from! (but don't look at me as a "ready made stuff sucker!  , I like to redraw myself pcb from the schematic I find on the net !)

At your knowledge is there a shematic for a Colour Organ using LEDs, the 1st link you gave are all for lamp and the 2nd one... you know too complex!

thx again for your help and efforts

[Mark Hammer]

If you built the buffer/splitter found here:  http://www.muzique.com/lab/splitter.htm (and remember you can add more outputs, as is mentioned in the article)....

And you build bandpass filters, a different range for each output, you can stick the envelope-follower section of this circuit:
http://www.muzique.com/schem/quack.gif   on the filter output.

Probably still too complicated, eh?  I'll look around and see if there is something pre-designed on-line that suits your needs.

[arma61]

thx Mark,very kind, and yes still too complex for me, if you find something pre-designed that will be better, it's a little bit hard for me also to search 'cause sometime I don't know the right words or combination of words to look for. In the mean time I've found a picture of the vu-meter I already build unfortunately schematic is not longer available, can something be done around this to achive  what I need ?

here's the link

[img=http://img205.imageshack.us/img205/7848/lx1353df9.th.jpg]

cheers m8

[Paul Perry (Frostwave)]

Hi I mean is it possible to let the Leds connected to the LM 3915 move based on the frequence of the audio signal (I'm thinking specially about wahwah) instead of moving at the voltage increase/decrease ?

If you mean, is it possible to have a LED display give an indication of the frequency setting of the wah, the simple answer is no.
That is, if you are looking at the audio output of the wah. Because, the output frequencies will depend on the music going into the unit as well as the setting.
For example, if your guitar note is 440Hz, as you move the pedal the mix of harmonics will change, but the main frequency will probably still be 440Hz.

If you would be happy with an indication of where the wah is set, that is another matter. you could use a dual pot, with the second pot generating a DC voltage to drive the display. But I think that might be covered by a recent patent. 

[arma61]

Hi I mean is it possible to let the Leds connected to the LM 3915 move based on the frequence of the audio signal (I'm thinking specially about wahwah) instead of moving at the voltage increase/decrease ?

If you mean, is it possible to have a LED display give an indication of the frequency setting of the wah, the simple answer is no.
That is, if you are looking at the audio output of the wah. Because, the output frequencies will depend on the music going into the unit as well as the setting.
For example, if your guitar note is 440Hz, as you move the pedal the mix of harmonics will change, but the main frequency will probably still be 440Hz.

If you would be happy with an indication of where the wah is set, that is another matter. you could use a dual pot, with the second pot generating a DC voltage to drive the display. But I think that might be covered by a recent patent. 

Thx Paul, I like the dual pot idea , but as  I said the wah fx is an autowah, so no pedal involved, just a pot to set the wahhhhh opening shape, but again I like that idea for my other bigger pedal board.

cheers