Date: Sun, 20 Aug 2000 19:57:34 +0100 From: Gavin D. To: FG Cc: keely Subject: [FG]: Hodowanec Circuit Hi all, for a while I have been an avid coiler, but have now decided to embark upon the exploration of more subtle energies. So I have turned away from the scene of high voltage currents to the realm of strange electronics. Naturally my first port of call was Hodowanec's work on gravity wave detectors. I have built the circuit on breadboard to see what exactly it did, but may build a "fixed" version on strip-board; full details of the circuit can be fond in the file grav3.html, otherwise I'll send a pcx file of the circuit to anybody who is interested. Anyway, the results. I first built the simple circuit but found it rather insufficient so I moved on to building the "improved circuit" as described in the grav3 file, this circuit gave better results due to greater total gain. Now, in the circuit diagram the value of sensing capacitor was stated to be 0.22, this could mean 220nF or 220pF, most likely 220nF considering standard notation. However, due to some of the frequencies stated in the file, I decided that 220pF was more likely.......I was wrong; I think the term is "ego-driven modifications"; 220nF works just fine! With the 220nF and the QND capacitor out of circuit, the output was low amplitude noise when the Gain potentiometer (RV2) was set to minimum (i.e. the wiper was right round to near ground). As the potentiometer was turned to maximum, there was a clear tone of around 750Hz (the out but of the circuit was connected to both a scope and simple audio amplifier). By adjusting the other potentiometer (the one in the feedback path from the first op-amps output to the inverting input, from now on RV1) this tone change in pitch, upto around 1.5KHz. When Gain RV2 was set between Tone and Noise, the signal sounded something like morse code. There was a general ELF signal modulated upon this tone, although it was not well defined. When the QND capacitor was connected into circuit, the out was pure noise. When the 220nF sensing capacitor was removed, the noise disappeared (only low level mains hum present), so the sensing capacitor was definitely the source of the noise (not the 741 op-amp which makes an excellent noise source in it's own right :-) ). Adjusting RV1 only influenced the general tone of the white/pink noise. I tried replacing the 220nF sensing capacitor with a 1000uF electrolytic as suggested in file grav3, this did not work to great. The signal sounded like a low frequency pulse train (say around 5Hz or so). However on the virtual scope (which tended to inject it's own noise, i.e the switch mode PSU for the laptop, around 3kHz) the signal was found to be a train of impulses or spikes, also amplitude modulated with the strange ELF signal. As spikes contain harmonics, the addition of the QND capacitor made no difference at all, the pulsing remained. I then tried a 100uF cap, this was best of all. Without the QND capacitor the output was again pulsing and the frequency of this could be altered by adjusting RV1. When the QND capacitor was connected, the pulsing only really ceased when both RV1 and RV2 were set to particular point (more of a certain minimum, i.e. a 3rd of the way round, when the frequency and gain were low enough but a signal was still present) When this was achieved, lower frequency pink noise was present at the output. This pink noise definitely had some structured, yet complex, signal deep within it. Just to check, I tried replacing the sensing capacitor with other components. First I left it open circuit, this resulted in very low level mains hum; the same as when a 220pF capacitor is connected. The I tried shorting to ground, this resulted in no signal what so ever, apart from some very low level noise from the op-amps. In contrast to this I connect a 10M resistor, this resulted in again low level mains hum. The most amazing result was achieved by replacing the capacitor with a piezo-electric element. After tuning my head to stop the acoustic feed-back to the headphones, I could hear every movement I made. When I dropped a softish item on the table, I heard a massive thud. Not only this, but I could hear a conversation from next door; I live in a detached house!! I also replaced the capacitor with two electrodes inserted into the ground. With both electrodes it was no different to shorting the inverting input to ground (as mentioned above). However, after removing the earth electrode connected the circuit ground, with only the inverting input connected to a earth electrode; the circuit gave a tone similar to when the 100uF capacitor was connected. The frequency of this tone altered as I raised the whole breadboard from the ground, increasing in frequency with height (obvious capacitive coupling, but at 100uF!?), it was only after a foot or so that I began to hear mains hum and typical natural earth current activity; all through a single wire. The best sensing capacitor was found to be a disc ceramic 220nF, other 220nF capacitors were tried. Well, that's it, read grav3 and give it a try. Regards, Gavin