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Old 6th March 2010, 04:08 PM   #31
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When you suggest to capacitively couple the coil I take it you mean by winding one coil directly over the other? Can you explain your comment above "that capacitively coupling will obtain the same results". I think that if a decent size transformer (VA rating) is used it should be able to handle a 555 at full output. You are probably right that a short duration pulse is a good logical place to start for a project like this then experiment later once things are working.
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Old 6th March 2010, 04:37 PM   #32
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By capacitive coupling i only meant using a capacitor to couple the 555 output to the coil.
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Old 6th March 2010, 04:49 PM   #33
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Default CD player used as generator

Hi analog_sa,
Quote:
Originally Posted by analog_sa View Post
A good beginning would be to open the commercial unit and take a few pics. As it appears from Scott's link, the coil is not very critical and i would think, neither is the waveform. As i prefer having a frequency display, or at least a source of an accurate frequency i will forgo the 555 and rather use a microcontroller.
I try different solutions for a Schumann resonator.
The first was my function generator. With this equipment, the frequency change with temperature. Even if Schumann resonance is 7.83Hz +/- 0.5 Hz, you can hear difference when varying the frequency from 0.01 Hz.
For an accurate frequency, I use an old CD player where I burn a continuous 7.83Hz sine wave. For the antenna, I put a 10mH inductor (from my stock) with a 600 ohm serial resistor onto the analog output.

I plan to build a generator with microcontroller, more friendly than CD player.

Correct me if I'm wrong, but the 555 is not able to provide a signal with 50% duty cycle. It generates 7.83 HZ with other high frequency.
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Last edited by Eric Juaneda; 6th March 2010 at 05:17 PM.
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Old 6th March 2010, 05:58 PM   #34
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These two site have lots of info on the 555 device. What size of area coverage do you get using the single 10mH coil? I will look forward to any and all micro controlled designs that may spring from this thread as I said that type of design is beyond my skills in electronics. I would be useful to have a device with multiple frequency settings and perhaps even various wave form settings. Thanks for the input Eric.

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Old 6th March 2010, 09:25 PM   #35
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Quote:
Originally Posted by Eric Juaneda View Post
Correct me if I'm wrong, but the 555 is not able to provide a signal with 50% duty cycle. It generates 7.83 HZ with other high frequency.


Some designs definitely use a 555. Acoustic Revive, otoh, do not. Just reversed their circuit (from pics in the review) and will draw and up it tomorrow if laziness does not prevail. The 8 pin device seen on the pics turned out to be a dual opamp. First half works as a relaxation oscillator and the second as a bandpass filter in order to turn the square waves into something prettier. A low pass should be equally effective. Split power is derived from the incoming 12v dc from two zeners and a virtual ground, so effective PS is probably +-4.7v. It seems AR gets better reviews than simple square wave generators so a sine wave is probably better. The pcb seems quite nice but component cost is way below $10 with the PS. Add a pcb and a case and total manufacturing cost is still under $40. No idea how much advertising and net buzz cost but they seem to operate on a pretty healthy markup.
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Old 7th March 2010, 03:24 AM   #36
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Old 7th March 2010, 07:29 AM   #37
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Hello Moray,
Quote:
Originally Posted by moray james View Post
What size of area coverage do you get using the single 10mH coil?
Oh, I see that I don't use 10mH but 1.2mH inductor! Sorry. The size of coil is:
- external diameter 44mm
- height 21mm.
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Old 7th March 2010, 07:37 AM   #38
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Hi analog_sa,
Quote:
Originally Posted by analog_sa View Post
...Just reversed their circuit (from pics in the review) and will draw and up it tomorrow if laziness does not prevail. The 8 pin device seen on the pics turned out to be a dual opamp. First half works as a relaxation oscillator and the second as a bandpass filter...
I already do this search .
In this schematic, the oscillation frequency can vary with the value of the power supply and temperature.
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Old 7th March 2010, 07:38 AM   #39
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Forgive me I was not clear in asking my question. I was wondering what size of radiating area that you have found your device to have? How far physically can you be away from the device and still perceive its impact?
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Old 7th March 2010, 10:50 AM   #40
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Here is the AR circuit. Some component values can be seen from the published pics but all should be easy to calculate as these are standard textbook curcuits. Opamp has a fet input and needs to have a low voltage offset. Output waveform is a modified square wave.
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File Type: pdf AR.pdf (12.4 KB, 819 views)
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