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Re: GOLDSCAN POWER
Interesting circuit. I am tinkering with one very similar using a 555 to generate the +5 supply. They do supply considearbly more current then the 7660, but also generate guite a bit of noise when switching. I have found that by running the 555 at from 1 to 3 khz I can still get enough current, and by synchronizing the transmitter pulse to the power supply it helps keep the noise spikes out of the receive time window. Needs a few more components,, but the advantage seems to be worth it. Like I said I'm still tinkering,, when I get something finalized I will post it.
Russ -
Re: GOLDSCAN POWER
Hi Russ,
With the values shown, the timer should run at 60 - 70 kHz. Not a good idea to use frequencies close to the TX rep. rate unless synchronised. Use a TLC or LMC 555 which give far less switching spikes than standard 555's. The choke L1 and its associated decoupling capacitor filter spikes trying to get back out. Pcb layout and placement of the circuit relative to the receiver is important. I don't know where L2 came from. It does not exist in the Goldscan circuit.
Eric.Comment
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Re: GOLDSCAN POWER
Hi Eric,
Is this your design? I went back and read Reg's PI write up and he mentioned Goldscan. The 740, 709, etc. sound like stuff you have mentioned before.
The schematics which are copied from units seem to have a fair number of mistakes at times, but heh thats part of the fun of building it yourself, and how people learn more about electronics and metal detectors, so don't fix em all ok?
JCComment
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Re: GOLDSCAN POWER
Hello Forum ,
It is right , L2 do not exist in Goldscan original ,it is for that i put a note : Option....
And for the mistake , you say JC , it is easy for the majority of the guys of the Forum to see if an errors exits? because of the electronic knowledge of manys and in one second they tell me an error of transcript in paper for the pot sensibility.( it is the marvelous Internet communication and it is easy also to catch misinformation).
and like i said this 100% schematic is FUNCTIONAL it's good, you can trust it , reproduce it in realtime.....and enjoy this brilliant detector.
The real thing it is to design with common sense a good printed board to optiminize his performance......
but sure you can also make smalls boards ie: the front end , pulse gene Ts555, pulse timing etc..... and hook all for test with many wires up in your labo and the result detector it still good for yours experiments..........
Have a good time all the forum .Comment
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Re: GOLDSCAN POWER
Hi alex,
Almost all schematics, even the ones made by the manufacturers have some mistake. Anyone who has ever made schematics knows how hard it can be to get every detail correct. You are right any little mistake will be found by the many on the Internet.
People often learn more from mistakes, be it life or electronics. I was just having some fun :o) I am sure there are no more mistakes on this schematic and it is functional. Good luck to all. And thanks again alex for the good information you have provided to all.
JCComment
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Re: GOLDSCAN POWER
I really had no idea that this was originally one of Eric's designs. Just never made the connection I suppose. I have been really having a great time trying different approaches to Detector design. This forum as well as the one Carl runs have been such a great source of information, and it has been a tremendous learning experience for me. When I first got interested in detector design a bit over a year ago I had a somewhat smug attitude about it, having almost 30 years electronics experience. How hard could it be?? Well my eyes have certainly been opened. I am very grateful to all the fine people who have shared their wisdom and expertise in this area. I may never build a really great detector, but the knowledge I have gained along the way in trying to do so will have made every minute spent in the attempt worthwhile.
RussComment
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Re: GOLDSCAN POWER
Hi Russ,
Yes, it is one of my designs, born after a visit to Australia in 1982. This convinced me that ground balancing was essential for a nugget hunting detector in those severe ironstone conditions. I made a shaft mounted detector called Goldscan 1, but only a few were made as the mechanics were too complicated. Goldscan 2 was next, with a chest mounted control unit with integral batteries. This was very popular and was made up till 1991. There was a high power version running off 24V which was Goldscan 3. From 1991 a return was made to a shaft mounted unit, but with a belt mounted battery pack and miniaturised lightweight electronics. It was just called Goldscan if made by me, or Goldscan 4 when made under licence by Pulse Technology. It is the schematic for this latter one that Alex has posted. There are a couple of errors in the main schematic which will prevent it working properly but any sharp eyed electronics whizz should be able to spot them.
I eventually stopped making PI's with ground balancing because most people used them on the beach where it is not generally needed. Maybe it is time to think about it again.
Eric.Comment
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Re: GOLDSCAN POWER
Hi JC,
That's correct. See my post to Russ below.
Eric.Comment
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Re: GOLDSCAN POWER
Hi Russ,
It is not too hard to build a really great detector, with all the information given and some common sense. You should be able to beat most of the commerical units as well. The best part is the understanding of exactly what your detector is doing, which often isn't completely understood in units you buy. This can go along ways to finding good targets. Also there is still room for improvements. But I have spent alot of time reading patents, schematics, building coils and electronics. Money and time wise it is easier and cheaper to just buy one. Fun and understanding wise you must build it.
JCComment
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Re: GOLDSCAN POWER
Hi Eric,
Thought this might be one of your designs after I looked at it. The diffential integrator and SAT/Autotune/ACmotionCoupling circuits are very novel. I came up with a diffinteg circuit some years ago which uses one resistor and one capacitor to do the + and - gain thereby negating any tolerance/temperature/humidity change in these parts verses using four resistors and two capacitors which will never really be close enough matched after integrating thousands of samples. The CMRR of the op amp doesn't matter with the resistors so far out of wack (i.e. 0.1% trimmed). It made a very noticable improvement in performance over the classic approach. Since the +/- is so close don't have to null it swinging in the earth field and most external periodic noise actually gets cancelled rather than some getting through due to the slight error in gain between the + and - inputs. Minelab has a second inverting op amp for the - signal fed to a single resistor and cap, this is better (maybe) but eat the offset of the second op amp which may be slow changing so doesn't matter, but there is a better way.
JCComment
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Re: GOLDSCAN POWER
Hi JC,
Tried to email you without success. Has your address changed?
Eric.Comment
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Re: GOLDSCAN POWER
Hi Eric,
You should have gotten the new email.
Changes depending on how much junk mail
I start getting on it. So every 6 months
to a year, depending on how well I guard
it.
JCComment
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Thanks JC.
Got your email OK.
Eric.Comment
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Re: goldscan pcb.
>Got your email OK.
>Eric.Comment
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