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I guess another name for this would be a frequency generator. Anyway, I have gone through several ideas with my dad (Electronics Engineer). The first was to use a 555 timer chip with resistors. I want a specific value of frequency though, and was lectured about the standard resistor values and the inefficiencies of the design. So he made on involving a PLL chip. You know, the ones for touch tone dialing? So That involved binary counters and a PLL, and a quartz crystal. But that isn't the best way to do it, because the binary counters would require button, and I want it so you can just play a tone, and a comparator can determine which value is greater and light up an indicator LED to show whether sharp or flat. So, is there any easy and practical way to do this without the purchase or making of a programmer (as my budget is too small for such a thing)? The people at Cemetech aren't familiar enought with PLL's to help me. I need to get the design solid before I waste money on parts. An IC is not my first choice. I want to make that clear. I have a SIMPLE AVR programmer that I made for the robot I designed. It only programs using the 6 pin programming method. Size is also a factor. I would greatly prefer something pocket sized over something desktop sized. I'm already familiar with surface mount soldering and PCB design. Any designs made in ExpressPCB, Eagle, or some other free PCB software are acceptable as help. THIS IS NOT COMMERCIAL! It's for my girlfriend, a musician like me. It's for her birthday. I want it to actually be accurate. So those are the criteria in the Engineering Design Process. The Constraints are pocket sized, and under $50 for parts (not resistors, capacitors, or other common stuff. I have plenty of those). So you professional design engineers that are here, help my design come into fruition. Thanks!

Off the top of my head, why not use a frequency to voltage converter (LM2917 I think). Feed the analog V out to the micro. You could then do math to figure out what note the input is closest to, then display how far off it is on an LED bargraph.

HEY!  That could be a design idea!  *chuckle*

OMG!! You just solved a problem I've been working for 2 weeks to think of how to use it! At times I wish I had a college education, but that's years in the future... :D So thanks John for the answer. If I need help on using it, I'll post again.

Well, it may not be the answer, as I said it was just off the top of my head (and without rereading the datasheet).

Unless she plays a flute I imagine some input filtering is going to be required. Input gain could be tricky, and AGC circuit trickier. But ... I think it could be made to work.

I'm a bit confused as to what you want.

If it's just an audio frequency generator, that's easy.

If you want to know the exact frequency of a tone, that's easy too.

You say you don't want any programmable devices but you already have an AVR programmer and a microcontroller is just what you need, even if it's just a simple tone generator. You can use a crystal for accurate frequency control so it never needs adjusting and it's easy to generate a squarewave with a known frequency out of an I/O port which can directly drive a piezo sounder.

To find the frequency of a tone is a little more tricky but it's still pretty simple. It should be pretty easy to convert the audio signal to a squarewave to monitor the fundamental frequency, decide on a tolerance and display the not being played. I'd  use the timer, for low frequencies you count the MCU's clock (or a division of it) over the period of the signal being monitored, for higher frequencies you count the periods within a clock interval.


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