Hi, i was just wondering if anyone on here could help me.
I'm looking to do a basic guitar tuning circuit for my a-level coursework in electronics, and have got the basic idea on how it would be done, i'm just a bit stuck with a few details. I want to basically plug the guitar in, and the circuit to get the frequency and compare it with what the frequency should be (possibly using the resonant frequency of a tuned circuit?) and then to implement a comparator to determine whether to light the flat or sharp LED. What i'm not sure about is how I'd convert the frequency input to a voltage to use in the comparator ciruict. After hours of google searches, I've found nothing, and am getting desperate!! I've seen a few previous posts trying to do the samething, but the links he was given are a little complicated for what i'm looking for.

Any help would be greatly appreciated, thanks :roll:

 

by the way, a frequency to voltage converter is defined as 'Frequency-to-voltage converters accept a signal and convert its frequency to a corresponding analog voltage level'. Is this what i'll need?

 

I'm a micro-controller kind of guy, and this is what I'd look into trying first. Don't know how well it would work though....

I'd get an AVR from Atmel with an ADC on it.
Take a few samples from the ADC and run a DFT on it.
Determine the frequency its at and compare it to what it should be.
Use PWM to light up 3 led's -> top led is too high, middle is just right, bottom is too low

Someone is probably gonna come in here and say something like, "Here's how to do it with a resistor, 555, and a bubble gum wrapper" though.

So what does "A-level" mean? I've seen that term here in the last couple days several times, but never before in my life. If I had to guess I'd say it means "associates degree" but like I said I'm unsure.

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I am more of a duct tape/baling wire kind of guy. One thought - use sound card, microphone and some fairly "common software" to indicate the freuquency.

I'm sorry I can't do better than "common software" at the moment but I've downloaded some amateur radio software that contains audio analysis displays - really cool stuff. It think it's safe to presume that you can obtain other similar stuff at no or low cost.

I realize that this is hardly something you'd build from scratch. I am not sure what you are limited to so I thought I'd mention it.

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stevez

 

The guitar tuner that I have ( Sabine ZIP-700) uses a LM358P (low power dual op-amp) for the input signal, and a motorola SC413349DW 28 pin IC, and a few transistors. Maybe that would give you some sort of start.

I'm currently tracing the board to figure the diagram to find the operation of the circuit, just to see how it works.

 

The UK magazine EPE did one based on a PIC a few years ago, it looked very straightforward.

BTW, for our western members, an 'A level' (Advanced Level) is an optional exam level taken in the UK between 16 and 18 years of age. You used to take 'O Levels' (Ordinary Levels) at 16 years of age, and then optionally stay at school an extra two years and take your A Levels. The O Levels have now been renamed GCSE's or something similar.

If you've watched (or read) Harry Potter, they are taking OWL's (Ordinary Wizarding Levels) - I wonder where that idea came from?. There's somethign similar with A Levels as well, but I can't remember what they were called.

 

One problem in looking for the frequency difference is that it will take a long time to determine that the difference is zero. You will be better off to actually measure the frequency and know when it is correct.

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Wow, thanks Nigel, it's nice to finally know what the heck an A-level is.

So do they have B levels and I levels (Beginner, intermediate)? It's pretty interesting to learn about other cultures.

 

http://www.apogeekits.com/frequency%20counter.pdf

here is a kit that does what you are looking for. It requires a microcontroller, but the schematic should show you how to capture the value of the frequency. If you hard coded the values for say E,A,D,G,F,B,e you could then simply compare the digitial value from the PIC with the stored value in a table.
E=329.63
A = 440
D = 587.33
G = 783.99
B= 987.77
e = 1318.51
(all values in Hz)

You could also check to see which value the note is closest too and automatically select the string that is being tuned, and then light up an LED if is high, lower, or right on.

 

http://www.circuitcellar.com/library...rzio/index.asp

Here is another site that also contains the code that you would need to run in a PIC16F84. These are widely available and cost less then $5. The download and figure include a full schematic as well as the code necessary to run the application. It also only uses LED's to display the readings. I think this is more of what you are looking for.

Good Luck!!!

 

There are various different qualifications these days, they seem to add extra ones every few months. But back in my day you took the 11+ (at 11 years old), the result of which decided which school you went to (either a Grammer School, if you passed - or a Secondary Modern, if you failed). At Grammer school you took your O Levels at 16, and could optionally stay on and take your A Levels at 18 - these than led you on to a University Degree. At Secondary Modern schools you left at 16, you couldn't stay on till 18, and you took CSE exams (Certificate of Secondary Education) - a top mark pass at CSE was considered an equivalent of just managing an O Level pass.

I passed my 11+ and went to 'Lady Manners Grammer School' in Bakewell, this was a great culture shock! - it was a great deal larger than my previous schools (about 600 kids at the time) and some of the teachers wore gowns and mortor boards - it was like going back to an old B/W film :lol:

 

Hi

actaully, Nigel, it hasn't changed much since 'your day'

to clarify slightly:

all people stay at school until the age of 16, when they take their GCSEs

then they can go into work, go to college to do a modern apprentaship, or go to a sixth form college (usually attached to a secondary school), and do these A-levels.

A-levels can be academic, or vocational (pratical based)

if you do academic A-levels, u can have the option of going to a university, and do a degree, or a gnvq (a watered-down version of a degree)

its much the same, but a few things added along the way just to confuse you!! - and they have dropped the CSEs...

sorry about the spelling!

 

You can build this around a http://567 tone decoderhttp://www.na...LM/LMC567.html and a few resistors and caps . Use 3 and indicate under-riteon- and above tuning

 

wow...thanks everyone!!
sorry for such a late reply, iv been havin trouble with my computer
i think i will end up doing something similar to the link aevans17 gave me, but does anyone know anything about frequency to voltage converters? my teacher thinks this is the best way to do it, to turn the audio frequency into a voltage and then use a comparator. a frequency to voltage converter is just essentially a fm demodulator (possibly using a monostable) anyone have any comments?

you'll probably hear from me again if i hit any problems and will let you all know how i get on.

thanks for all your help!!

edit: just a question, Noggin, could you please explain what you mean by

'I'd get an AVR from Atmel with an ADC on it.
Take a few samples from the ADC and run a DFT on it.
Determine the frequency its at and compare it to what it should be.
Use PWM to light up 3 led's -> top led is too high, middle is just right, bottom is too low'

an AVR, a DFT and a PWM please? i'm not familiar with the abbreviations, thanks

 

That isn't really a good idea. If you convert the frequency to voltage, then measure the voltage you will not have a very precise tuner. ADC's are not 100% precise, especially if you are using an 8 bit ADC because then the value can only be between 0-255. ALos, depending on temperature, other electric noise your measurements will differ. Counting the period of the wave, and will give you an exact measure of frequency of the incomming sound. This eliminates any of the error that may arise durring conversion and ensures that you are measuring the wave form exactly. The second link that I posted does exactly this.