Low voltage sine wave output

[dvhenry]

Hi, it.s been about 30 years since I previously had electronics as a hobby, I'm a bit rusty on the details.

I have a problem to solve, it requires a 60 KHz sine wave output at 5V peak to peak, preferably from a small 9V battery.
Voltage and frequency can vary by 5% and required amperage out is very low (the small 9V battery should hold sufficient charge for about 24 hours)

I am hoping for some advice on what chip to use, where to find appropriate info on that chip, and would greatly appreciate any tips that may be offered.

 

[BobK]

To get 5V p-p from a 9V battery you are going to need a bridged amplifier. If the current is really small (20ma or less) two op amps driven 180 degrees out of phase would do. A simple phase shift oscillator using another op amp could provide the signal. So you could build it all with one quad op amp and a few resistors and capacitors.

Bob

 

[dvhenry]

Thanks very much for the advice, can you recommend a suitable quad op amp?
I'm happy to start searching the details to get it working as desired (but may be back with further questions).

 

[BobK]

LM324 would probably work out.

Bob

 

[dvhenry]

Thank you, I will have a close look at it, your help is much appreciated.

 

[dvhenry]

Hi, back again, I have made some progress in understanding op amps and the ways to use them for various applications, but I can't help feeling I may find a simpler or more suitable solution if I first discuss the purpose and tolerances a little (something I should have done to begin with). So here goes.

I have a broken ankle that after 16 weeks is showing very little sign of healing (healing time should be 6 to 12 weeks).

There are noninvasive methods that have been shown to decrease healing time considerably.
One of these is electrical stimulation, of the electrical stimulation methods capacitive coupling, where electrodes are placed on the skin either side of the fracture and a low voltage is constantly passed at a frequency 24 hours a day has shown to be the most effective in situations like mine,

Yep. I'm skeptical about this also, but it is based on scientific evidence, including experiments done by noting bone growth increase with a DC voltage applied to 2 electrodes on a bone.
What makes me most skeptical about this is the price that is asked for these devices, they are however supported by health systems in the US and much of Europe (although it appears not Australia).

As for the tolerances I mentioned, these have produced the best results for similar situations to mine in assessments of multiple surveys.

60 KHz 5V p-p sine wave.

(the surveys included 20-200 KHz 1-10 V many without information on the wave form used)

The use of 9V battery is optional,the appropriate number of AAA 1.2V rechargeables is probably a better option.

I can do this easily with a 555 timer, but of course, not in sine wave.

Any ideas or suggestions appreciated.

 

[BobK]

I misread your OP as Hz instead of KHz.

I tried simulating my idea with an LM324 and it was not capable of enough gain at 60KHz to output 5V p-p. You would need a faster rail to rail op amp to make it work. But it does look like it would work.

I cannot think of anything simpler. You are going to need an oscillator and an amplifier.

Bob

 

[BobK]

Here is a circuit that does what you want. I produces a 5V p-p sine wave at 60KHz. The op amp used is a 5MHz GBP single supply op amp. Any op amp with similar performance should work.



You will probably have to adjust the resistors in the phase shift network to get the right frequency and the gain on the second op amp to get the right amplitude. Use trimmers to do this. You can adjust a single resistor in the 3 RC phase shift network and the feedback resistor on the gain stage.

I would also recommend using the 4th op amp in a quad package to buffer the midpoint voltage which is fed to the + inputs of the other op amps.

Bob

 

[dvhenry]

Thanks for the time and effort you have put into this so far.
That should do the job nicely, I may have more questions but I will research them first.

 

[KrisBlueNZ]

BobK, nice work! (BTW your output is 10V p-p; you could manage with a single-ended output stage, and a dual op-amp.)

 

[BobK]

I always get confused about the meaning of p-p. It seems to be used as either the single sided peak of a symmetric waveform, or from the positive to the negative peak. Looking it up on Wiki, though, you are right, I have 10V p-p and you only need one op amp to amplify if you want 5V p-p which is from -2.5V to 2.5V. You can just leave out the second op amp inverter, and take the output between the single output through a 1uF cap to ground.

Bob

 

[BobK]

Here is the circuit modified to put out a 5V p-p (-2.5 to +2.5V).



Bob

 

[dvhenry]

,Thanks Bob and Kris, I apologize for the delayed reply,

In the meantime I have ordered a budget bench top oscilloscope, it should arrive in a week or so, located and dusted off my old supply of resistors, capacitors,etc, and attempted to dust off my memory as well (It's been 30 years or so,so that last bit seems the hardest.)
Oh. and the specialist downgraded the radiologists last X-ray assessment from delayed-union (delayed healing of the fracture) to non-union, Clearly done to make my day!

But back to the subject. I've had difficulty, even with the all the great advice given so far, in identifying a suitable op amp chip.

Could someone suggest a suitable part, by part number? Then as long as I can find the data sheet for It I should be able a find a suitable chip, Well that's my theory.

Thanks.

 

[BobK]

You are right it is hard to find a single supply 5MHz op amp that will operate at 9V.

Here is one that would work.

http://www.digikey.com/product-detail/en/TLE2142CP/296-10464-5-ND/380986

Bob

 

[dvhenry]

Bob, once more, thank You.

 

[dvhenry]

Hi, it's taken awhile but the two TLE2142CP op amp chips I ordered arrived yesterday.
Before I continue with the project I would like to confirm that I have the diagrams correct and have not made an error that may damage the chip.

I found Tina-TI and am using that to make the diagrams.
The first is the block diagram of the TLE2142CP, (Tina-TI displays the op amp symbol differently to in the diagrams previously shown on this thread, with the Vcc- and Vcc+ swapping positions).


And here is my attempt to rearrange the most recent diagram made by BobK on this thread (post #12), to suit the above.


If someone could look at these and let me know if they are OK or have errors that need to be changed, and what those errors are, it would be much appreciated.

Also I'm unsure where the second output should be on this diagram.

 

[KrisBlueNZ]

That looks right to me. It's pretty hard to follow, but if you have to work with an 8-pin block instead of two op-amp symbols, it's impossible to make it clear like Bob's original drawing.

I'd suggest adding a decoupling capacitor across pins 8 and 4 of the IC. In this case, a 0.1 uF ceramic capacitor would be fine. Something like http://www.digikey.com/product-detail/en/C420C104K5R5TA7200/399-4491-1-ND/818348 (axial - one wire out each end) or http://www.digikey.com/product-detail/en/C320C104K5R5TA/399-4264-ND/818040 (radial).

It's also common practice to decouple the VCC/2 voltage; to do this, add a similar capacitor between pins 3 and 4 of the IC.

 

[dvhenry]

Hi Kris, I understand that the diagram is difficult to follow and thank you for putting in your time, effort and expertise to follow it. I did start over a few times but unfortunately that was the best I came up with.

I'd suggest adding a decoupling capacitor across pins 8 and 4 of the IC. In this case, a 0.1 uF ceramic capacitor would be fine. Something like http://www.digikey.com/product-detai...91-1-ND/818348 (axial - one wire out each end) or http://www.digikey.com/product-detai...4264-ND/818040 (radial).

It's also common practice to decouple the VCC/2 voltage; to do this, add a similar capacitor between pins 3 and 4 of the IC.

So,I add C6 and C7 here?

By the way,the software automatically changes 0.1uF to 100nF, I have no say in the matter.

While You are looking at this, where is the second output taken from?

Thanks.

 

[KrisBlueNZ]

Yes, C6 and C7 are right.

You take the other electrode from the 0V rail of your circuit, i.e. battery negative or pin 4. The output voltage appears across R8.

BTW I would use a higher value for R8 - something like 10k. That just reduces the load on the op-amp and decreases the power consumption slightly. I'm not sure why Bob specified 1k but I think he will agree that 10k would be better.

 

[dvhenry]

Thanks Kris, R8 at 10k, done.
It looks like The diagram is ready to to move to some physical testing, I still need some capacitors and a few other minor parts, but I should be able to get those locally.
I will be back here when it is at that point (hopefully with good news, but more likely with more questions).

Thanks Bob and Kris, I would have been stuck without your help.