Electronic experts or simply someone who know how to do this!

[Kaneezi]

Hi,


First of all i hope you'll excuse grammar mistakes, i'm still learning english!


I'm a member of a junior audio club and recently discovered the accoustic revive through the father of another member.

Our funds are very limited, so i plan to build a portable sine wave generator based on a schematic i found.

My plan is to make it available to others members of the club (they'll need to solder though).

My issue is that i would need help to design the circuit, the rest i can take care of.

This circuit might interest other diy enthusiasts too!

This is the link to the schematic


Thanks and take care!


Kenzi.

 

[JonSnell Electronic]

That is an ELF oscillator. Not audible. Google Colpitts/Hertley oscillator.
Colpitts Oscillator Tutorial and Colpitts Oscillator Design

 

[Kaneezi]

Hi JonSnell,

you are correct this not audible, the frequencies are meant to be broadcast via an antenna (the accoustic revive use a pcb antenna)


I don't really how to clarify/redraw the circuit and i have never used CAD.

If i posted in the wrong forum sections (Design & Build - Construction Tips) could someone move this thread?

I posted here because i found relevant informations in this thread


Thanks!

 

[wwenze]

Erm... well... hmm...

Well if you want to produce a sine wave for wireless transmission the quickest way is to follow the most common method - something that output a square wave (easier to make compared to sine) that goes through a band-pass filter. An analogue output driver for wireless at e.g. 2.4GHz would be too... well... hard to build.

But if you intend to transmit a 7.83Hz wave... wait actually it says "pulse"

the RR-77 generates a 7.83Hz Schumann frequency pulse

Well, again, multiple ways to skin a cat, textbook methods from an electronics course from the 80s may not make economic sense to the consumer now. An oscillator either sine or square + band-pass or even an MP3 player... and still cost less than the enclosure.

In short, the oscillator isn't really the issue. Getting what you intend to do sorted out first is more important (power? waveform?).

 

[Kaneezi]

Hi wwenze,

i thought about that (using a band pass filter) but doesn't know where to start! (is it difficult?)

It seems that following the schematic might be easier!

I won't try to pulse the frequency (seems more complicated)

Testing it with a breadboard is ok (a bit messy!) but i would really like a cleaner schematic and i try to follow CAD tutorials but it is a bit complex for the moment.

I already have the pcb antenna based on the accoustic revive, what matter from what i read is the sine wave at the precise frequency of 7.83hz

I chose a portable device to be placed behind the head (behind foam, while sitting) instead of a larger device.

What matter is a clean sine wave frequency tuned to 7.83hz (this is the only requirement)


Thanks!

 

[wwenze]

An MP3 player will produce cleaner and more precise-frequency sine than any textbook oscillator made up of a few passive components and some transistors.

 

[Kaneezi]

An MP3 player will produce cleaner and more precise-frequency sine than any textbook oscillator made up of a few passive components and some transistors.

Really? last year we did some tests on mp3 players (on human hearing ranges) and found distortions on lower frequencies (10hz - 8hz i think)

I don't have an oscilloscope here right now so i cannot test it.

I finished building a 555 square wave generator and tested it with a multimeter and i read 7.83hz (i chose a prototyping board but it's still very small!)

Could i use a band pass filter on this circuit to convert the square to sine wave?

I will probably have to build another one to compare the two (square and sine).

Thank you for your help, this forum is great! i will probably have all ready for class!

 

[Mooly]

An MP3 file at high enough bit rate should be very good. Remember CD distortion levels are microscopic on sine testing.

Try making your own test files. You can make MP3's or WAV etc with Audacity.
http://www.diyaudio.com/forums/soft...ing-using-audacity-get-you-started-guide.html

The tiniest amounts of distortion on a sine wave are audible as a 'harshness' creeping in. A 555 circuit will never filter down enough to get a clean sine from, certainly not without zillions of components in the filter.

 

[Kaneezi]

Hi Mooly,

if i remember correctly we tested 320kbps and used audacity (i should do it again myself to be sure)

If this is correct a simple (and very small) mp3 player should be enough! (could an amplifier be connected?)

How low (frequencies) can a mp3 play? i don't find informations sources on this (i find mention of binaural beats but nothing more)

I know that i wrote that i think it is maybe too complicated but what about pulsed frequencies with audacity, is it possible?

A 555 circuit will never filter down enough to get a clean sine from, certainly not without zillions of components in the filter.

Well i'm happy to have made it, even if a mp3 player is the best choice!

I don't really understand the need of larger devices if an mp3 player and amplifier can play clean low frequencies, is there a reason?

 

[Mooly]

I suspect cheap MP3 players will vary a lot and probably not go down all that far. My cheapo Philips spec gives 45Hz to 16Khz as the response. A PC soundcard will be much much better than that and should go down to around 5Hz or lower.

 

[Kaneezi]

So mp3 players are not the solution! (except expensive ones it seems!)

What are the alternatives? i know that a dds signal generator such as the ones on ebay are a possibility (small & portable so this good) but the price is an issue for 10+ people.

I understand that designing a circuit based on the schematic will take time, is there an online service who do that?

 

[Mooly]

If you have access to a scope then just try some MP3 files and see how they look at low frequency. Don't take anything on trust... try it and see You might be pleasantly surprised.

 

[Nico Ras]

If you already made a 555 square wave then you can pass this through a low pass filter to make it sine wave.
The simplest way to get a very low distortion is to use a multi-pole filter. Here is an 8 pole elliptical filter in a single component with only a few external components and includes an uncommitted op-amp.


http://datasheets.maximintegrated.com/en/ds/MAX293-MAX297.pdf

 

[Kaneezi]

Mooly,

I will definitely try that!

Nico Ras,

I looked at the datasheet (a bit complex for me) but very interesting!

I looked at low pass filters and what i read is that the results is close to very close to sine wave but not described as pure.

What i see from schematics and actual circuits trying to reproduce the revive are generating square and not sine waves (which is not the case of the accoustic revive)

(even if this seems very complete is there a cheaper alternative than the max293/297?)

In just a day i already learned so much, thanks!

 

[jcx]

some DAP have "capacitorless" outputs - the 1st iPod Shuffle would go down to single digit Hz

output DC blocking caps in single supply portable likely will be no bigger than needed for audio
but when driving a high Z >10 kOhm any should go low

however many Audio DAC chips include internal digital highpass filter of a few Hz

you simply have to test - but with .flac or .wav - a codec has no reason to keep sub 20 Hz content

 

[cbdb]

Why don't you spend time on something that actually might improve your audio?

 

[Kaneezi]

Hi jcx,

you simply have to test - but with .flac or .wav - a codec has no reason to keep sub 20 Hz content

Most mp3 players (the cheap ones) support mp3 and wma do you think they could filter lower frequencies? (i will try to find more informations on those models)

Hi cbdb,

club members are all happy to participate as well as our music teacher, and this is fun i'm learning many new things!

(maybe i'm not understanding your message, is it a question?)

 

[Mooly]

No promises but if I have the time I'll try it tomorrow on an MP3 player and look at the result on a scope. I'll also record a pure 440Hz tone from a synthesized digital function generator and from a traditional Wien bridge oscillator and let you see if you hear the difference.

 

[Kaneezi]

No promises but if I have the time I'll try it tomorrow on an MP3 player and look at the result on a scope. I'll also record a pure 440Hz tone from a synthesized digital function generator and from a traditional Wien bridge oscillator and let you see if you hear the difference.

Wow! that's so nice of you!

Thanks Mooly!

 

[wwenze]

The codecs themselves can be forced to go as low as you want, here's the options in LAME for example, but this is just for the sake of saying.

The DAC would be the bottleneck. Load would be high anyway - since the generators/DACs by themselves wont drive an antenna at 7.83Hz and even if they can the passive components would be huge - so you'd need an active filter.

What i see from schematics and actual circuits trying to reproduce the revive are generating square and not sine waves (which is not the case of the accoustic revive)

This I forgot to consider - did anybody measure the output of acoustic revive? (Or even a schematic so it can be predicted?)

We might be trying too hard here. Considering most antennae have a narrow frequency range and won't even see much of the 2nd harmonic, even a square wave would work.