Frequency detector/decoder

[KMS]

I have some ideas about making a new sound device (top secret for now) but it would help me to find some schematics on some existing frequency detector/decoders.  Some schemo that will detect preset and/or variable LFO or HFO frequencies and then actuate a relay or CMOS flip flop once the selected frequency is detected...... I need to get a handle on this.

Does anyone have a reference/link for this type of info?

Maybe there is an IC all set up for it?  If so the schematic for the IC would help.

Thanks,

Kurt

[KMS]

Thinking out-loud here....

One idea I have is using a discrete notch booster and then run the output from the filter into a flip flop or a nand gate which would turn on an LED once the desired frequency was detected.

Does that sound doable?  I guess I could wire it up and see but it would be nice to get some DIY discussion first or a link with some info so I could see what some of my options are.

[KMS]

Oh and try to guess what I'm trying to build 

OK....I'll tell you.

An Auto Octivator...that turns on and then off for preset frequencies.

[TELEFUNKON]

http://cache.national.com/ds/LM/LM567.pdf

discontinued, but still available

[Paul Perry (Frostwave)]

It's very difficult to do, if you have a signal with more than one frequency in it. Even with only a single note, it is difficult because of the overtones changing as the note rings out. Plus, it has to decide pretty quic, making the problem more difficult still.
But, why not try with something based around the filters used in a "color organ", those kits that drive colored lights depending on frequency? You could compare the levels of the detected bands to decide when to switch.

[KMS]

Thanks guys,

The color organ idea.....good.  I built one when I was 14...1974...my first etch too.  I don't know why I didn't think of that.....blank spots in my old age.

I know that there will be overtones.  My hope is to set it up so it triggers when the frequency has max output...which should be when I play the chosen note.  It will no doubt be easier for low frequency notes.

I might put a variable pot (with foot control) to assist with adjusting the level of the detected signal prior to the nand gate or flip flop as the detected trigger level will change with different chosen frequencies.

I think I can make it work for at least one note for a given song and then set it up (preset) for the next song. Would be real hard to do on the fly. Seldom would I use the device, but it would be nice to have for real high one note octaves that are otherwise impossible to hit on cue.

I could stomp it on at a convenient spot just prior to the desired note and then conveniently stomp it back off (or lower the detected level with foot pot) after the Octave is no longer needed and hopefully avoid false triggers.

[KMS]

The LM576 idea..the link didnot work...but I found it anyway...that looks good also and brought me to finding some other stuff

Found here http://www.reconnsworld.com/audio_tonedecode.html

I can see that the RC section is a notch filter and I could use this set up and build variable filters for several bands or ranges (the more quantity smaller bands the better accuracy of the notches) with the bands set up on a rotary switch to choose different ranges while using only one IC.

Thanks

[calpolyengineer]

There is actually a little circuit based on the 555 chip that I have in a Forrest Mims book. It is set up so that you can turn frequency into voltage, sounds like that would be pretty much what you need. Unfortunately, I just went home for spring break and left the Mims book at school. If you still would like to see it, I'll get it up eventually.

-Joe

[Paul Perry (Frostwave)]

Those frequency decoder circuits (like the one based on the 555) only work on good clean single frequencies. Otherwise you have all the same troubles you have with a Blue Box or similar octave divider.

[calpolyengineer]

Yeah, I thought you might say that.

Well, I was looking around at other stuff and found this: http://www.diystompboxes.com/smfforum/index.php?topic=34250.0

I have read that at hammer.ampage.org but didn't even think of it when I saw this thread.

-Joe