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Offline gizmo
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« Reply #20 on: May 16, 2010, 12:10:17 pm »
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can these boards be used with a prexisting coil? Idea

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Offline darkkitten2000Topic starter
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« Reply #21 on: May 16, 2010, 12:52:25 pm »
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Hmm, yes if in 1.1mH inductivity range 10% up or down may be tolerated.

regards,
d.

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« Reply #22 on: August 01, 2015, 10:34:02 am »
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Hi everyone,

i finished building the ETI561 but i have some problems.... it works only when i put my hand close to IC2, when i remove my hand it starts ticking slowly until it stops and i don't hear anything from the speaker. also when i touch one of the search coil wires with my finger at the pcb board and another finger on IC2 it works even better. what could be the problem?Huh?? any idea Huh?


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« Reply #23 on: August 01, 2015, 06:57:00 pm »
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   Check everything around IC 2...    The Oscillator is not working it sounds like.   Bad Cap is my bet.   Or X is sick.     

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« Reply #24 on: August 31, 2015, 02:50:02 am »
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i like to build that too but styroseal capacitors are not available to our country csn you sdvice any capacitor i might use?



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« Reply #25 on: August 31, 2015, 07:09:53 am »
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    Aluminized Mylar should do the job.

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« Reply #26 on: May 17, 2016, 02:51:29 am »
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hi i want to build 50cm loop or coil

please Tell us a few ohms and several micro-Henry؟

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« Reply #27 on: July 03, 2016, 05:44:22 pm »
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Hey!
I´m new here. I´ve built the ETI561 with some modifications. First I tried a Discrimination but it DOESN´T worked, the eddy currents are bigger than the flux changes due to ferromaterial. Ferromagnetic metal causes increasing frequency, non-ferrous metal causes also increasing f. Only a ferrite rod decreases frequency  Cheesy

I added two voltage stabilicers to the circuit, one for the search oscillator the other one for the detection circuit and reference oscillator. I hope this will isolate the oscillators better than the original circuit. Now one battery is enough. I changed the dual 4013 for the crystal divider to a 4024, now you have a more universal divider by 2,4,8,16,32,64,128 switcheable via jumpers. This is great for experimentation, using different crystals, coils etc.

Sensitivity is good, 1€ at 20cm in free air, 18cm coil.

I want to make some professional PCBs. Is anybody interested? PCB is 35x100mm, I want to buy a batch of 20 from ITEAD but don`t need them all.

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« Reply #28 on: July 05, 2016, 12:57:29 am »
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Hi
Another newbie here -first post.
I also made one of these a few weeks ago just out of curiosity.  Sourcing the polystyrene caps in the oscillator proved to be the most difficult part as I could not find any online. In the end I resorted to paralleling several odd values from the junk box to get close to the required values.
It worked quite well in a 'cobbled together' form and I plan to wind a small 70 - 100 mm diam coil to see if it could be made into a pin-pointer when I get more spare time. Unfortunately it is going to have to wait for now as the other repair jobs are piling up and I keep getting side-tracked. Nice to hear that others are still building  this design though!


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« Reply #29 on: July 06, 2016, 05:46:38 am »
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The circuit has a big disadvantage: The tuning of the oscillator by adjusting the bias! This is easy but not the perfect way. The bias should be at 1/2 Vcc for best working, not below and not above. At the lowest and highest end it is very unstable and the little tuning range is sometimes annoying when testing different coils. A piece of shielded wire for the search coil has big effect in frequency change due to parasitic capacitance. A bigger tuning range from low to end would be more useful.
But what about a varactor? BB112 could do the job. Is something against a varactor in the search oscillator?

Making different coils is very time intensive. You have to wound a few turns, shield it, tape it. THEN you can measure it > Mostly the frequency is not right > dismantle the coil, remove some windings, shield it again and so on...
A bigger tuning range would be more practicable, definetely.

Maybe it is possible to change the styro capacitors by NP0 ceramic capacitors. Or polypropylen (MKP,FKP) capacitors.

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« Last Edit: July 06, 2016, 05:49:53 am by horstiborsti »
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