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So Ron, just curious how long it is until your patience with this guy runs out, with his WIREs and COILs and all.
Does anyone even know what the hell he's doing with this stuff? any idea what the application is, what the physical configuration of these WIREs and COILs and whatnot is? what he's trying to control here?
All I can say is, you're a better man than I ...
I mainly trying to control Cameras at a distance, [...]
Well, OK, that tells us a little about your application, but not much. Controlling cameras based on what? proximity of something to a long wire or a coil? (I ASS-U-ME that by "WIRE" you basically mean a long length of wire connected at only one end, essentially an antenna?) And what form/shape does the "COIL" take? Is it in proximity to whatever you're trying to capture with the camera?
It would really help to know this stuff. Of course, speaking for the congregation here, we understand that you might not want to disclose proprietary information. But barring that, any details you can give--especially the physical layout of this setup--would help to give you better answers here.
And you know, you don't really need to capitalize "WIRE" and "COIL" in your descriptions; we can figure out what you're referring to.
I know that a darlington has a very low input current so its input resistance is very high.
I simulated an ordinary transistor and a darlington that uses the same collector and emitter resistors. The gain of the darlington is half the gain of the ordinary transistor.
A Jfet does not have much voltage gain. Why don't you use an audio opamp that has Jfet inputs (like a TL071 or OPA134)? Its input impedance is extremely high and it has as much gain as you need.
It sounds like you need an automatic-volume-control like were used on some tape recorders. It is also called a compressor/limiter and is used by radio stations.
Usually it is very noticeable because when the sounds are low then it boosts their level and the level of noise. When sudden loud sounds occur then the AVC circuit responds too slowly giving a blast of very loud sound before it reduces the level. When the sounds suddenly go to a low level then they cannot be heard until the AVC circuit resonds by increasing the gain.
Correct me if I'm wrong, but I think you are trying to servo on the amplitude of the 2 circuits? So whatever the gain you have on one you need on the other.
Since you have a micro I think I would just clamp the output to the A to D at 5 volts then let the micro set the gain to the input stages to bring them into optimum range (2.5 volts). (calibration) This of course would require a new design, but it's probably a requirement anyway. The next step would be to determine the maximum and minimum signal from the 2 different COILS when the gain is the same but they are at maximum and minimum distance from the WIRE. This spec. will limit how far away from the Wire the COILS can be, which may be another problem?
It really would help if you could explain how you would like the whole system to work.
A bit of explanation of what I do, as I keep getting asked: I photograph wildlife and anything interesting, and have been interested in electronics for a long time, but never mastered it as you can see. I wanted to adjust Cameras at a distance and at first used radio control and Binoculars, then Wifi, with my sons help. Then I tried relaying the signal to get the long range. The WIREs seemed best, so here we are. I am also interested in Generators and I have designed a linear Engine with a Motor engineer. While he gets on with the engine side, my side is to design the electical side, this is where the coil experiments help my understanding. This technology lends itself to many ideas, and WIRE following has been suggested and sounds interesting, so these circuits might come in handy for that too. So now you know more than I do about what I'm up to, I hope it helps.
So you basically want to remotely control a digital camera from a distance, correct?
Sheesh. What a wild goose chase this whole agonizing exercise in ADD has been.
Don't you realize that there are perfectly good, tested and debugged solutions for this available?
What kind of distance are we talking about here, anyhow? yards? hundreds of yards? miles?
Your AGC circuit has too many things wrong for me to fix it. Look in Google for a good one that uses a single polarity supply.
Your "clamp" diode allows the input of the comparator to go too low below ground which messes up its output polarity.