The idea is that most MCUs have an in-built EEPROM memory, that you can use to write and read from. Its actually simple if you use MPLAB and the XC8 compiler. All you need is to change some bits in a register and send the data to the EEPROM or read it from it. The information will stay in the EEPROM after the MCU is turned off.

 

In that case, it would be much better to use a simple potentiometer. The potentiometer will always remember the value, so to speak.

That might actually make for a reasonably simple solution. The tuner wouldn't automatically capture the tuning of the master instrument, but it could be quickly calibrated to match it. You just need a trim pot, a few comparators, a few LEDs...

The workflow would be:

• Adjust trim pot until neither sharp nor flat LED is lit, indicating that tuner matches master instrument.
• Take tuner to each other instrument and tune it until you've got a match.

It replaces the original button push idea with a little bit of knob turning, but it might be the best option if microcontrollers are ruled out.

 

In that case, it would be much better to use a simple potentiometer. The potentiometer will always remember the value, so to speak.

How could I use a pot?
Could I turn it to the “master” frequency and set?

 

That might actually make for a reasonably simple solution. The tuner wouldn't automatically capture the tuning of the master instrument, but it could be quickly calibrated to match it. You just need a trim pot, a few comparators, a few LEDs...

The workflow would be:

• Adjust trim pot until neither sharp nor flat LED is lit, indicating that tuner matches master instrument.
• Take tuner to each other instrument and tune it until you've got a match.

It replaces the original button push idea with a little bit of knob turning, but it might be the best option if microcontrollers are ruled out.

That sounds like a good idea, any chance of a circuit diagram?

 

That sounds like a good idea, any chance of a circuit diagram?

No promises on timing... it'll probably be a few days, maybe more, before I can draw anything up. First though, I'll need a few numbers from you.

• What voltage(s) is/are available for powering additional circuitry? 5V, 12V, some other voltage?
• You said earlier that you could tap into the signal inside this meter to get a voltage corresponding to pitch. I need to know what voltages you get for pitches near the top and bottom end of the scale.

A very rough, conceptual schematic could be created without these numbers, but if you want useful part numbers and component values I'll need the requested voltages.

 

I've also previously requested those voltages.
The meter voltage should be taken across the meter, and from each meter terminal to the battery minus terminal for at least a half-scale reading of the meter.

 

No promises on timing... it'll probably be a few days, maybe more, before I can draw anything up. First though, I'll need a few numbers from you.

• What voltage(s) is/are available for powering additional circuitry? 5V, 12V, some other voltage?
• You said earlier that you could tap into the signal inside this meter to get a voltage corresponding to pitch. I need to know what voltages you get for pitches near the top and bottom end of the scale.

A very rough, conceptual schematic could be created without these numbers, but if you want useful part numbers and component values I'll need the requested voltages.

I’ll try to get that info to you tonight as best I can

 

No promises on timing... it'll probably be a few days, maybe more, before I can draw anything up. First though, I'll need a few numbers from you.

• What voltage(s) is/are available for powering additional circuitry? 5V, 12V, some other voltage?
• You said earlier that you could tap into the signal inside this meter to get a voltage corresponding to pitch. I need to know what voltages you get for pitches near the top and bottom end of the scale.

A very rough, conceptual schematic could be created without these numbers, but if you want useful part numbers and component values I'll need the requested voltages.

ok guys,
ive got some numbers

the meter is powered off a single 9v battery

The voltage between the positive input of the terminal to the negative of the battery is 3.063v
The voltage between the negative input of the terminal to the negative of the battery is 3.135v

the range we would be looking at would be between 470hz and 490hz
I put my meter across the terminals of the meter and measured at 1hz intervals using a tone generator in front of the mic as follows

470 0.147v
471 0.157v
472 0.166v
473 0.176v
474 0.186v
475 0.195v
476 0.205v
477 0.215v
478 0.225v
479 0.234v
480 0.244v
481 0.254v
482 0.263v
483 0.273v
484 0.283v
485 0.292v
486 0.302v
487 0.312v
488 0.322v
489 0.331v
490 0.341v

hope this is enough info, let me know if you require any more and I will provide if I can

thanks so much

 

ok guys,
ive got some numbers

the meter is powered off a single 9v battery

The voltage between the positive input of the terminal to the negative of the battery is 3.063v
The voltage between the negative input of the terminal to the negative of the battery is 3.135v

the range we would be looking at would be between 470hz and 490hz
I put my meter across the terminals of the meter and measured at 1hz intervals using a tone generator in front of the mic as follows

470 0.147v
471 0.157v
472 0.166v
473 0.176v
474 0.186v
475 0.195v
476 0.205v
477 0.215v
478 0.225v
479 0.234v
480 0.244v
481 0.254v
482 0.263v
483 0.273v
484 0.283v
485 0.292v
486 0.302v
487 0.312v
488 0.322v
489 0.331v
490 0.341v

hope this is enough info, let me know if you require any more and I will provide if I can

thanks so much

That's great info! It's very interesting. I'm intrigued by the ~3V offset. I'm wondering if either terminal on the meter stays constant. If the 3.063 or the 3.135 never changes, then it's potentially a simpler circuit, since we would only need to pull one signal out and do comparisons.

If both voltages move, and it's only the difference between them which is meaningful, then the first stage of the new circuit would need to be a differential amp. I don't have a problem with that, but it would make the circuit a little more complicated and expensive.

Either way, I'm glad to see a very nice, linear frequency to voltage relationship. Should be reasonably easy to work with.

 

That's great info! It's very interesting. I'm intrigued by the ~3V offset. I'm wondering if either terminal on the meter stays constant. If the 3.063 or the 3.135 never changes, then it's potentially a simpler circuit, since we would only need to pull one signal out and do comparisons.

If both voltages move, and it's only the difference between them which is meaningful, then the first stage of the new circuit would need to be a differential amp. I don't have a problem with that, but it would make the circuit a little more complicated and expensive.

Either way, I'm glad to see a very nice, linear frequency to voltage relationship. Should be reasonably easy to work with.

Do you need me to check anything else?

 

If

Do you need me to check anything else?

If you could spot check the reading from each terminal to battery negative for just a few frequencies, that would be great. Maybe 470, 480, 490Hz? That should tell me whether the new circuit needs to monitor the positive input terminal, the negative one, or both. Thanks for gathering this data. Good stuff!

 

Do you need me to check anything else?

At what frequency does the meter show zero mechanical movement?
What is the mechanical meter reading for 490Hz.
Need to know the meter voltage for the maximum meter reading you will ever likely have.
Does the meter have a center zero or starts it start from the left of the dial?

 

At what frequency does the meter show zero mechanical movement?
What is the mechanical meter reading for 490Hz.
Need to know the meter voltage for the maximum meter reading you will ever likely have.
Does the meter have a center zero or starts it start from the left of the dial?

I only need to deal with between 470 and 490

 

If

If you could spot check the reading from each terminal to battery negative for just a few frequencies, that would be great. Maybe 470, 480, 490Hz? That should tell me whether the new circuit needs to monitor the positive input terminal, the negative one, or both. Thanks for gathering this data. Good stuff!

ok,
the positive terminal on the meter input to negative doesn't change from 3.063
however the negative terminal on the meter to negative reads as follows for 470 480 and 490
470 2.917v
480 2.821v
490 2.725v

hope this helps

 

ok,
the positive terminal on the meter input to negative doesn't change from 3.063
however the negative terminal on the meter to negative reads as follows for 470 480 and 490
470 2.917v
480 2.821v
490 2.725v

hope this helps

Sweet! I think that's all I need for now.

Gonna be busy probably the rest of the night, but I'll let you know when I've got something... or if I realize I still have questions.

 

Sweet! I think that's all I need for now.

Gonna be busy probably the rest of the night, but I'll let you know when I've got something... or if I realize I still have questions.

thank you so much for your help

 

thank you so much for your help

Ok, this one may be annoying, but I realized there's one more detail that would help determine the best approach. I need to know if that stable 3.063 voltage (or any of the others) varies significantly depending on battery voltage, or if all the internal working voltages are regulated. A 9V battery can range from almost 10V brand new to less than 7V before many "9V" circuits stop working.

If the signal levels change in relation to battery voltage, we can make this circuit scale in a similar way. If it doesn't, then we can use regulated reference levels.

The best way I can think to check this would be to measure the battery voltage, and double check that the positive meter terminal voltage is still near 3.063V. Hopefully the current battery reads significantly lower voltage than a new battery so we can see the change. Then put a brand new battery in and measure its voltage, then measure the positive meter terminal again (all of these measurements relative to battery negative terminal)

Sorry to be a pain, but I'd hate for this circuit to give wildly unpredictable results depending on the battery state of charge, and there's no way to know how the existing circuit behaves without testing it.

I've done a rough simulation of the concept I have in mind, and everything's working great so far. Once I know how battery life affects signal readings, I should be able to fine tune things a little more and share the basic circuit simulation.

The first schematic will be in LTspice simulation software and will neglect some generic background details like decoupling caps. Once we're happy with that circuit concept, I can draw a cleaner, easier to read version with all the extra components in DipTrace.

 

Ok, this one may be annoying, but I realized there's one more detail that would help determine the best approach. I need to know if that stable 3.063 voltage (or any of the others) varies significantly depending on battery voltage, or if all the internal working voltages are regulated. A 9V battery can range from almost 10V brand new to less than 7V before many "9V" circuits stop working.

If the signal levels change in relation to battery voltage, we can make this circuit scale in a similar way. If it doesn't, then we can use regulated reference levels.

The best way I can think to check this would be to measure the battery voltage, and double check that the positive meter terminal voltage is still near 3.063V. Hopefully the current battery reads significantly lower voltage than a new battery so we can see the change. Then put a brand new battery in and measure its voltage, then measure the positive meter terminal again (all of these measurements relative to battery negative terminal)

Sorry to be a pain, but I'd hate for this circuit to give wildly unpredictable results depending on the battery state of charge, and there's no way to know how the existing circuit behaves without testing it.

I've done a rough simulation of the concept I have in mind, and everything's working great so far. Once I know how battery life affects signal readings, I should be able to fine tune things a little more and share the basic circuit simulation.

The first schematic will be in LTspice simulation software and will neglect some generic background details like decoupling caps. Once we're happy with that circuit concept, I can draw a cleaner, easier to read version with all the extra components in DipTrace.

Ok, so the current battery reads 8.66v and it gives 3.064

A brand new battery reads 9.77v and also gives 3.064

 

Ok, so the current battery reads 8.66v and it gives 3.064

A brand new battery reads 9.77v and also gives 3.064

Excellent! Thanks for more good data. The good news is that your whole system should be very stable - the bad news is I need to rework the reference side of the circuit just a little. Pretty close though...

 

Excellent! Thanks for more good data. The good news is that your whole system should be very stable - the bad news is I need to rework the reference side of the circuit just a little. Pretty close though...

that's great news,
thanks