Building a Guitar Tuner with a 555 Timer IC to Generate 440Hz Tone

Please review my blog posts on Science 2.0 here and here regarding my trial and error building a 440Hz tone generator out of a 555 time IC.

I'm trying to build the circuit with as few components as possible. Am I headed in the right direction using the CSS555C?

Seems to me the 555 wouldn't be temperature stable enough, not even with high quality resistors and an NPO capacitor. And, also, wouldn't you want it to output a sinewave?

I would use a crystal oscillator, instead. Like a 32768 Hz and divide it down to 8 Hz (using, for instance, a CD4060) and then use a Phase Lock Loop (PLL) [CD4046] to multiply it by 55. That way, you can use a voltage controlled sinewave oscillator (XR2206CP) for the output that would be synced to 440Hz by the crystal oscillator.

You might also want to throw a variable cap on the crystal to tweak it into compliance.

Or, you could generate the sinewave with a ROM that feeds a DAC.

Or, do it with a microcontroller -- with a microcontroller you have the oscillator, prescalers and timers that could be used to get 440 Hz and then PLL to a sinewave output, or even use PWM to an RC filter to get a sinewave (it will have a bit of distortion, but that should be fine for this application). OR, rather than PWM, a serial feed to a serial input DAC.

If using a PIC, most of the 8bit pics have TIMER 1 that has it's own oscillator. Use the 32768Hz crystal to run Timer 1 and then use the internal osc (typically 8Mhz) to run the logic. Not all of them have both, so use the selection guide at Microchip:

* http://www.microchip.com/maps/microcontroller.aspx

PIC 16F872 has three timers



The operating mode is determined by the clock select
bit, TMR1CS (T1CON).


In Timer mode, Timer1 increments every instruction
cycle. In Counter mode, it increments on every rising
edge of the external clock input.
Timer1 can be enabled/disabled by setting/clearing
control bit TMR1ON (T1CON).
Timer1 also has an internal “RESET input”. This
RESET can be generated by either of the two CCP
modules (Section 8.0). Register 6-1 shows the Timer1
control register.
When the Timer1 oscillator is enabled (T1OSCEN is
set), the RC1/T1OSI/CCP2 and RC0/T1OSO/T1CKI
pins become inputs. That is, the TRISC value is
ignored, and these pins read as ‘0’.
Additional information on timer modules is available in
the PICmicro™ Mid-range MCU Family Reference
Manual (DS33023).


Using Timer0 with an External
Clock
When no prescaler is used, the external clock input is
the same as the prescaler output. The synchronization
of T0CKI with the internal phase clocks is accomplished
by sampling the prescaler output on the Q2 and
Q4 cycles of the internal phase clocks. Therefore, it is
necessary for T0CKI to be high for at least 2TOSC (and
a small RC delay of 20 ns) and low for at least 2TOSC
(and a small RC delay of 20 ns). Refer to the electrical
specification of the desired device.
5.3 Prescaler
There is only one prescaler available, which is mutually
exclusively shared between the Timer0 module and the
Watchdog Timer. A prescaler assignment for the
Timer0 module means that there is no prescaler for the
Watchdog Timer, and vice-versa. This prescaler is not
readable or writable (see Figure 5-1).
The PSA and PS2:PS0 bits (OPTION_REG)
determine the prescaler assignment and prescale ratio.
When assigned to the Timer0 module, all instructions
writing to the TMR0 register (e.g. CLRF 1, MOVWF 1,
BSF 1,x....etc.) will clear the prescaler. When assigned
to WDT, a CLRWDT instruction will clear the prescaler
along with the Watchdog Timer. The prescaler is not
readable or writable.

Timer2 is an 8-bit timer with a prescaler and a
postscaler. It can be used as the PWM time-base for
the PWM mode of the CCP module(s). The TMR2 register
is readable and writable, and is cleared on any
device RESET.
The input clock (FOSC/4) has a prescale option of 1:1,
1:4 or 1:16, selected by control bits
T2CKPS1:T2CKPS0 (T2CON).
The Timer2 module has an 8-bit period register, PR2.
Timer2 increments from 00h until it matches PR2 and
then resets to 00h on the next increment cycle. PR2 is
a readable and writable register. The PR2 register is
initialized to FFh upon RESET.
The match output of TMR2 goes through a 4-bit
postscaler (which gives a 1:1 to 1:16 scaling inclusive)
to generate a TMR2 interrupt (latched in flag bit,
TMR2IF (PIR1)).
Timer2 can be shut-off by clearing control bit TMR2ON
(T2CON) to minimize power consumption.

Your getting a bit confused Steve with 8 bit timer2, 8Mhz, FOSC/4 , watchdog timer and timer zero

Its risk achitecture so external to internal instruction time clock is FOSC/4 and you set the desired prescale to further increment on clock in ratios of

1 : 2
1 : 4
1 : 8
1 : 16
1 : 32
1 : 64
1 : 128
1 : 256

Typically if oscillator frequency is 4mhz for example then timer ferquency 3921.50 Hz

So an interrupt occurs every 255 counts of timer0 for example having an instuction time of 1 us with prescaler ratio set to 1.1

Try this to work out your prescaler settings plus shows you how you can derive various interrupts

Vary usefull little tool this

If you are intending to use assembler this is also a very usefull little tool for creating delays

makes programming alot lot easier for those of you who like to waste time you see like me Thats if you enjoy wasting time writing code in order to learn something new

Then after youve wasted all this time you can go create you see like microsoft do and earn stacks of money and get barred from maplins for a whole year because youve upset the management with a question , which would help them to develop sales and become that much more interesting to talk too and buy goods from

Two years later you can even get a letter of appology from them as well

You can even buy pic micros from them as well
As long as you buy pic micros from them and pay cash thats ok but dont come back to the store because your barred

Classic !!

Good isnt it

Still Never mind !! Nothing to worry about

All true this All good news

Good isnt it

Still Never mind !! Nothing to worry about

All true this All good news this

Or after you’ve wasted so many years or so and have learnt most of Microsoft’s software which you pay dearly for and having learnt all the backdoors and how they crack serial numbers which is a security floor in Microsoft’s software Then what you can look forward to as a degree student on very low support and being very intelligent You can look forward to being fined £5000 by Microsoft

That’s intelligence for you Not as you might think offer him a job he’s brilliant No lets fine him

What do you reckon on that attitude then isn’t that just so positively clever , such fantastic encouragement not so Collin ??

What do you reckon on that then Collin

Do you think this works then I mean its good for business isn’t it creates employment certainly makes people want to learn . good positive attitudes some of you hmmm Super

Those are people I would employ straight away i wouldn’t even contest this They are this brilliant They can find those mistakes in my software that I’m using with which im going to possibly develop applications for banks , executive companies with the end risk of if i don’t know what those flaws are

The country risks being completely bankrupted over night

Or better still my Military of defense , my last final wall between the enemy and my country has just been infiltrated and they’ve managed to launch 12 nuclear war heads

Thos are people you look after encourage not fine £5000 or as you put Collin , “Why waste your time writing software “ especially when there is no employment or very little work or people stuck with no skills

I’m staggered at these attitudes

Or lets puts some reporter into prison because theyve managed to hack thier mobile phones all because theyve been exposed downloading pornographic matarial as in the latest scandal surrounding news reporters Even though the police pay people "Known fact " to do just that hack thier phones

Wouldn’t it be nice if we got a couple of these blokes , women mustn’t be sexist,” Got to be ever so careful these days you just never know do you ” , to infiltrate the defense institution of South Korea just as they are about to launch and redirect their missiles back at them even better right back into their Silo’s

And how do you think people communicate in secret then Collin by mail , maybe but then mail gets intercepted What about inside an integrated circuit then Collin

No not thought about this then , Or maybe that information is embedded into your processor on your PC or mobile phone and through a series of GSM commands unknown to you they watch and listen to every call , message etc you make

That’s quite important I would have thought particularly defense applications banking applications security aware applications Or do you think that’s a waste of time too especially when it comes to emergency calls or

What’s going to happen if when you produce a controlled environment application and they manage to hack the streams and all of a sudden you wind up with bills in your home in excess of a couple of thousand pounds not knowing how this has happened all because you didn’t bother to get your software tested

How you going to do this without wasting your time writing software for embedded architecture

Im going to let you think about this hard , very hard

I was referring to the Timer1's capability to drive it's own crystal.

From the 16F616 datasheet regarding the Timer 1 Osc:

bq). *6.4 Timer1 Oscillator*
A low-power 32.768 kHz crystal oscillator is built-in
between pins OSC1 (input) and OSC2 (output). The
oscillator is enabled by setting the T1OSCEN control
bit of the T1CON register.

This is separate from Fosc. Also, I was talking about a more "Modern" PIC like the 16F616 which has it's own internal osc (Fosc)

But, I was way off on using a 32768 osc to achieve 440! Instead, use a crystal on the Oscillator Module (Osc1 and Osc2 inputs) (or perhaps the internal osc is stable enough). This will be Fosc. And then use the timers to work out the timing for something like one of the following scenarios:

1. A 440Hz square wave on a CCP output (set to PWM and 50% duty cycle)
2. A serial stream to a serial input DAC
3. An 8-bit/10-bit/12-bit parallel output to an 8-bit/10-bit/12-bit DAC
4. A modulated PWM output that will produce a near sinewave when RC filtered.
5. A stream of 1s and 0s that will produce a quasi-sine wave using the technique outlined here:

* http://www.romanblack.com/BTc_alg.htm

Other inspiration:

* http://www.romanblack.com/onesec/SineDDS.htm

.......

Mark, you often provide a wealth of pertinent information in your replys, but, dang, what is all this other crap that is totally unrelated to the question? I wouldn't mind, except that it fills my inbox with junk that I have to sift through, and it fills these threads with junk that people will have to sift through to get to the related material! Indeed, some of it is rather funny and some of it is worth saying, BUT NOT ON THIS FORUM!

You're making a mess out of these posts!

Is it Steve tell me what are your youngsters going to do when they leave school whi wull design for you then

Who will rebiuld the future if this is your idea of technical standards

What do you think of this then have a look at the latest technical schematic on Makita drill chargers and tell me what you think about this

This is fully serviceable down to component level Yes its surface mount components but what do you call this

How do you classify this as engineering ? ,"Quote the reply I received not that this is the fault of the employee but

This is all the technical information they get from Japan "Its pathetic " might as well employ under age school children " Tell you what why even bother to educate them at this rate

This is not enngineering Steve this is just rubbish

What exacty does this teach you to do except replace a bourd "how degrading can this get " Would you classify this as engineering I dont

Even you know better than this

End price £74.51 RS Components

Component cost worst ways probabaly about £10.00 But we dont repair these anymore Ebay price $66.00

Why dont we just kiss engineering goodbye might as well

Thats RS out of bussiness

Drill price anywhere btw £99.00 to £159.00
inclusive charger and we wondering why we have such a economic problem

Rents for shop keepers London alone on average £600 plus per week Rates £ 50 plus perweek Poltax on shop £25 per week Electric £20.00 per week Water rates £10.00 per week

Thats a small shop No employees , No wages , No stock and finally we get to this stage


Honestly what are we teaching people to do these days


Makita by the way is quite q well known brand of power tool not cheap or wasnt till the advent of the net Then we arrive also at the so called summits to discuss the level of poverty etc not to mention recycled equipment and of course polution

Here is a copy of the email

Hi

I am sorry but that is the only drawing that we are supplied from Japan.

Regards

Mark Banyard

Well come on steve your the big shot you tell me what this teaches people to do other than use a screwdriver

Pop over to india quckly or china , or tiawan you can even buy yourself a worker aged 12 maybe possibly slightly older that you can exploit

Yes thats what this amount too


See below

I think: _What the f*** does any of this have to do with advising a guy on making a minimal component guitar tuner?_

Next Steve your a good engineer tell me what’s wrong with this schematic Why is this making popping noises and why are the United states reluctant to allow people here to modify this amplifier After all its class D shouldn’t making popping noises should it

Why won’t the United states co operate when we ask for service information including Hifonics USA

No your are the big shots here You tell me what’s wrong with this so I can go back to over 100 distributors and explain why this does this and why we cant get answers out of the United stares after all your top notch engineers Aren’t you

Well You are though so you tell us


Diagrams below

Id like a full report on this as well Consider this your opportunity to prove me wrong

Whats this got to fo with a guitar tuner quite a bit I would have thought seeing as you cant even get this right and another company is about to go bankrupt as a result of this so called technical expertise

Minimul component guitar tuner ?? Hmmm

Fast Fourier transformations might be the right answer usng amicus 18 developement bourds

That what I might classify as providing key training keeping people up to date and showing them how to do this the right way instead of this backward development path

Another possibility:

The PIC16F1455 and PIC16F1459 (also the PIC16LF1455 and PIC16LF1459) both have a 5-bit DAC that could be used to produce a crude sinewave -- still better than a square wave, and because only one frequency is being produced, it would be an easy low-pass filter.

Mark, as noted you sometimes do have good ideas but there is so much repetitive rant that I no longer read anything you write, so anything useful you say is lost completely.

Perhaps you could condense your rant into one large document that we could access at if we really need some random ranting.

At this point my biggest disincentive for visiting this site is your contributions. Is it your intention to drive people away from this site?

Believe it or not this is not a vindictive personal assault. You have every right to your ideas. I however have a right not to have them forced on me in the guise of answering technical questions.

could you just use a low pass filter on the square wave itself?

I wouldnt bother we finished anyway why should you worry so dont bother but then also dont bother to learn anything new either after all why would i ever want to do bussiness with the USA given these attitudes Hopefully after weve taken someo f your companies to the cleaners in the Uk they wont bother either

There you go easily solved That’s my answer and since these companies actions and failure to c operate with people in the Uk is going to cost them their homes I can therefore determine from this that these actions can be considered as an act or war against the UK

So as far as so called allies are concerned I can now regard the USA as enemy number one

Thats also fair comment as well

Yes you can. But it's a trade off between how pure the tone is (i.e. how much harmonic content) and the complexity of the filter(i.e. order and type). A square wave is composed of the fundamental frequency and odd harmonics. Being that the next harmonic is 4x the fundamental, it is a little simpler to filter than, say, a sawtooth wave and you might get away with a first order filter (i.e. a simple resister and capacitor), and, in fact, if you set the cross-over frequency lower than 440Hz, you'll get a better result, with the drawback of reduced amplitude (i.e. you might need an amplifier after the filter).

But, a sinewave approximation from a DAC (even a 5-bit DAC) will filter better. And, PWM should also produce a resonable result, especially if the carrier frequency is much higher than 440 and even better if it's a harmonic of 440.

But, it all depends on how pure the tone needs to be.

Make that 3 times the fundamental -- analog is not my strong suit

Actually, temperature is not too much of an issue. I'm usually using it at home at room temperature. Now, if I was on a campout up in the mountains then the temperature change could come into play.

As far as using crystal oscillators are concerned, I'm actually trying to build as simple a circuit as possible so that anyone from 8 to 80+ could build it--from second grader to octagenerian.

The PICAXE 08M microcontroller can generate 440HZ tone with a couple lines of code--but it seems a waste of a microcontroller. Nonetheless, thanks for giving me an material for a later article.

duplicate post.

Well, then, it is probably fine. I wonder about component tolerances, though. Haven't done the math, but you might want to research the resistor, capacitor, and 555 tolerances and how much they would affect frequency. In other words, is 1% tight enough to keep the frequency from ranging beyond what someone can detect with their ear? How about if you combine a 1% resistor with, say a 2% capacitor? And then add in the variances in a 555.

The 555 is fairly stable and fairly immune to supply voltage changes (perhaps use a regulator if not good enough), but the human ear can be pretty sensitive to frequency differences -- down to 2 Hz at 440Hz.

Ok. here is the simplest circuit I could build--it makes a 247 HZ tone (after adjusting the 100K pot about half way) which is the open B string on a guitar:

So, this assumes that the builder/user has the means to set the tuner to 247 Hz -- will that necessarily be the case?

Also, I would add a resistor in series with the pot and reduce the pots value (e.g. 42K resistor in series with a 20K pot), so it is easier to tune it to 247 Hz and also make it less vulnerable to drift -- or are there other frequencies it needs to be tunable to?

And, as Colin pointed out, the piezo will probably detune and otherwise alter the tone (might even modulate it). If so, then try adding a voltage follower transistor amp between the cap and the piezo.

Voltage follower: http://en.wikipedia.org/wiki/Common_collector

The piezo device can go in place of Re.