# School Project - Any help requested

#### Schwhat

##### New Member
Hello everyone,

I'm new to this website as well as circuits (I'm taking a university Physics-related electronics course) and I'm seeking some guidance, so I hope I've come to the right place.

I want to create a dummy guitar tuner that only tunes to one single frequency. (Doesn't matter what that note/frequency is). I've found several guides online that are much more complex than I intend to pursue. I want my circuit to take in an audio frequency through a microphone, verify that it is that certain frequency, and output some visible function that acknowledges the frequency is correct (LED light, for example).

Several websites suggest using counters including this one. I've read through some other posts here that suggest using frequency counters and some people are against using those.

Does anyone have any ideas on how they would go about getting started on this?

Any feedback would be GREATLY appreciated.

#### dr pepper

##### Well-Known Member
Its an old chip now but its still around the Ne567, its a Phase locked loop tone decoder, and it sdesigned to do just that light an Led on a specific frequency.
It can be setup for various frequencies and bandwidths.
I'm designing a circuit with one presently, but its Rf not audio.
A more elaborate approach would be to amplify the signal to the point it clips then count the frequency with something like an arduino.

#### Nigel Goodwin

##### Super Moderator
Its an old chip now but its still around the Ne567, its a Phase locked loop tone decoder, and it sdesigned to do just that light an Led on a specific frequency.
It can be setup for various frequencies and bandwidths.
Good call, it's a VERY useful little chip, and ideal for what he needs.

#### DrG

##### Active Member
This is a serious question and not sarcasm or something else...

Code:
Harmonic lock Check for harmonic locks (phase lock between harmonics of input signal and of VCO). When Vi is a low level sine signal, the PD works in linear range, and harmonic locks can occur for VCO harmonics (the VCO signal is a squarewave, with harmonic content), that is for input frequencies fi near the VCO resting frequency (For): Fi = K For  (K = 1, 2, 3 ...). When Vi is squarewave, or a high level sine (which causes saturation in the PD), lock can occur for input frequencies which are integer multiples of For: J Fi = K For (con J, K = 1, 2, 3, ...).
from: here

It would seem that using that PLL might not work out for guitar tuning - no?

Looks like the OP must use an Arduino for the project <--sarcasm

Edit: oh wait, the harmonics wouldn't be there to be locked if the fundamental was not the correct frequency, so it would work...save the Arduino for the next project.

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#### Schwhat

##### New Member
Thanks for the speedy responses!

Okay, so I do own an Arduino Uno R3 from a little starter kit. I was thinking about adding another component to notify a user that they're hitting that particular frequency in addition to an LED light. (A motor with a tiny weight attached for vibrations). Would I be able to use the NE567 for this as well?

#### Schwhat

##### New Member
I've already created a pre-amplifier for the incoming sound waves; I've heard that the white noise can give some useless input. My biggest problem is going from a microphone to Arduino. I can't seem to find any guidance on how to program the arduino for incoming frequencies.

#### DrG

##### Active Member
Thanks for the speedy responses!

Okay, so I do own an Arduino Uno R3 from a little starter kit. I was thinking about adding another component to notify a user that they're hitting that particular frequency in addition to an LED light. (A motor with a tiny weight attached for vibrations). Would I be able to use the NE567 for this as well?
I want to create a dummy guitar tuner that only tunes to one single frequency. (Doesn't matter what that note/frequency is). I've found several guides online that are much more complex than I intend to pursue. I want my circuit to take in an audio frequency through a microphone, verify that it is that certain frequency, and output some visible function that acknowledges the frequency is correct (LED light, for example).
The 567 solution seems to be simple and elegant as long as it works and it would seem to, at least potentially, do just what you said you wanted to do. Why not give that a try first? I was being more silly than anything else by bringing up an Arduino. Now, if you change your specifications, that is another matter. In that case, maybe settle on exactly what you want to do first....and Yes, you may find yourself getting into more complex situations than you intended.

Get a 557, read the specs, build the circuit, hook it up to your mic and preamp, solving voltage issues and the like. Generate a frequency and see if you can get that to light an LED. That's what I think anyways, because that may be complicated enough. There is plenty of help online - see https://www.instructables.com/id/Sonic-Control/ for example. Then expand or try to measure frequency with the Arduino without the 567, or in addition to the 567. That's what I think anyways.

#### rjenkinsgb

##### Well-Known Member
With the 567, you also have the option of connecting a centre-zero meter between pin 2 and a potentiometer across the supply (to match the "locked", on-frequency voltage on pin 2).

That would give a low or high indication if the the 567b is locked to the incoming signal but not exactly on frequency.

#### DrG

##### Active Member
With the 567, you also have the option of connecting a centre-zero meter between pin 2 and a potentiometer across the supply (to match the "locked", on-frequency voltage on pin 2).

That would give a low or high indication if the the 567b is locked to the incoming signal but not exactly on frequency.

According to the datasheet, "Bandwidth adjustable from 0 to 14%", so it should perform well for what the OP originally said he wanted to do.

It could definitely be done with an UNO - this is actually a pretty nice looking "instructable". That project is using the guitar pickups as the "mic", but I don't see why he couldn't use it with an electret and a pre-amp. I even like the Instructable that the code is based on. While I have not looked too carefully, they both seem to be much better quality than I normally see...from those.

#### dr pepper

##### Well-Known Member
Schwat I Pm'd you a link to a guitar tuner project from a popular electronics magazine.
Its from 1982, but all the parts except one are standard, the one that isnt is the 50240.
Theres a harmonic filter on the guitar amp to remove harmonics already discussed, and it uses a frequency locked loop to compare a divided down xtal oscillator to the guitar, an interesting concept.

#### Nigel Goodwin

##### Super Moderator
There was a full guitar tuner based on a PIC in an old EPE magazine.

Here's a nice simple one, using hardly any parts:

#### dr pepper

##### Well-Known Member
Nice & simple.
If the guitar & 7555 were in sync and 90 degree shifted the led would always be out, but thats not going to happen so its a nifty and simple circuit.
I'd have posted the article I Pm'd but for some reason I thought that wasnt the done thing.