Circuit assistance request

For the electronics crowd. I have been working on this (intermittently) for a while now with not much success. What I am making is an arduino based guitar tuner, with the amp and barebones arduino on a single board. The attached eagle schematic is the result of a bare bones arduino schematic, and an amp with DC offset schematic (both found in other projects) bolted together.

With the amp/DC offset breadboarded, and connected to an arduino uno, I receive correct data in the serial monitor when playing each string, so it seems that all is well in the circuit.

As seen in the schematic, the IC used is a dual op amp with a dual supply. I only need a single op amp, and would like to use a single 9V battery power source.

So how do I make this happen, I’m guessing it isn’t as simple as selecting a different IC and deleting one of the batteries.

RBBB_Arduino_tuner.sch (378 KB)

Just to be sure I understand… The circuit works on the breadboard, but currently used two nine volt batteries in addition another power supply for the arduino. And you would like to remove one of the batteries. Is that correct?

Is it really a TL082 op amp, or just something with a similar footprint? Looking at the datasheet, I think you are mistaken about it having two different supplies. The TL082 has to op amps, but they share a single VCC and ground, pins 8 and 4.

This chip is getting 18 volts from these two batteries. I’m entirely sure what’s going on with the single line out of the middle of the two batteries.

What happens if you remove the bottom batter and connect pin 4 to ground. One effect would be drop the supply voltage down to 9 of course. But just removing it without making the ground connection definately won’t work.

It seems I have misunderstood what a “dual supply” op amp means. I was thinking dual power supply …

I’m an idiot … I mean a noob…

Anyway, the project I am building is one I found here

As I understand it (and the instructions), the chip receives 18V, and the arduino is powered off of the same supply. This is also how I built it on the breadboard

What I am attempting to do is build the amp circuit and arduino into a single board, so I don’t have to buy another arduino.

So with that in mind, before I design a board, and send it off to OSH, does this schematic look correct?

Of course you will want to do the WHOLE thing (including your barebones arduino) on the breadboard first, but it looks like it should work the way you have it. Good job.

That top 9volt battery is supplying power to the voltage regulator which is supplying 5 volts to the arduino circuit. That bottom battery is just being used by the op amp in conjunction with the unregulated 9volts from the top one before it goes into the voltage regulator to provide 18volts.

The thing to remember about voltage is that it’s all relative. Most of the time it’s relative to a common ground, so 9 volts is 9 volts. But it’s perfectly legit to have a difference from something other than ground and that’s what’s happening with that bottom battery. The positive of the top battery is 9 volts relative to ground, but 18 volts relative to the negative of the bottom battery. So the op amp chip gets to enjoy 18 volts, the voltage regulator gets 9v, and everything else 5v from the regulator.

If you do do the whole thing on a bread board, be careful of those 18 and even 9 volt bits. They will totally fry the atmega chip if you accidentally let them come into direct contact with the 5 volt parts.

If you’re really concerned about the supply, plug in an LM78L05 or LM78M05 voltage regulator circuit between +9V and 0V, outputting to the AVR power supply. If you do that and use proper capacitors, you should have plenty of power for the AVR, it’ll be smoothed out by the regulator and capacitor combination, and you will have the digital and analog supplies separated, which will decrease the noise in the audio line.

He’s got one in there already. Actually, an L4931, but it’s serving that same purpose.

I was just cautioning that while breadbording it, since this circuit has an 18 volt componant, care be taken not to accidentally let those 18 volts touch the chip.

I’m not married to the L4931, I could swap it out for a 78X05 if it would make for a cleaner audio signal.

I must have missed the L4931 in the schematic when I looked at the one on Instructables.
Or maybe Instructables misses it on the webpage, and I didn’t look close enough.

Either way, I’d use the L4931 if you can. It’s an LDO which means the battery can drop to a much lower voltage without the regulator being unable to regulate any further.

Usually I reference an LM7800 series for people who need help because its easy to use, simple to design around, and available from almost any supplier. I missed a detail here, and should have kept quiet. Sorry.

No need to apologize, I'm greener than a trashy girl on St. Patricks day when it comes to electronics. And for that reason I'm always open to suggestions.

The one on the instructables doesn’t have it because it uses a full arduino, so you didn’t miss it. It’s just in Jon’s, as part of his arduino circuit.