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Old 6th March 2015, 07:56 AM   #1
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Default Electronic experts or simply someone who know how to do this!

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.
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Old 6th March 2015, 11:33 AM   #2
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That is an ELF oscillator. Not audible. Google Colpitts/Hertley oscillator.
Colpitts Oscillator Tutorial and Colpitts Oscillator Design
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Old 6th March 2015, 12:16 PM   #3
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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!
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Old 7th March 2015, 05:39 AM   #4
wwenze is offline wwenze  Singapore
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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"

Quote:
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?).
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Old 7th March 2015, 06:36 AM   #5
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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!
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Old 7th March 2015, 08:59 AM   #6
wwenze is offline wwenze  Singapore
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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.
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Old 7th March 2015, 11:18 AM   #7
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Quote:
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!
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Old 7th March 2015, 11:35 AM   #8
Mooly is offline Mooly  United Kingdom
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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.
Installing and using Audacity. A get you started guide.

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.
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Old 7th March 2015, 12:31 PM   #9
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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?

Quote:
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?
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Old 7th March 2015, 01:24 PM   #10
Mooly is offline Mooly  United Kingdom
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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.
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