Falcon MD20

[Friiman]

Think it´s 0.20mm wire, showing 0.22mm.
Its hard to measure so tiny wire when i cant grab it so good.
Need to calculate the coil winding now, not my best skill. But there is plenty calculator for it, but i dont know how to enter the information to get it to show 140 or 150uh and the resistance at about 2ohm
Somebody know how to make the search coil?

[kt315]

i do not see on-line calculator for a coil on ferrite rod, as there noticed it is hard to calculate. so i did calculate without
ferrite. it give me 80-90 turns for 100 uH - i decrease 150 to 100 because ferrite increases the L value.
so you may wind same and after measure, then wind off turns step by step while you would get this 140-150uH.

[WM6]

If coil inner diameter is 5.1mm (9.7 - (2.3+2.3) = 5.1) and wire gauge AWG32 (0.20mm),
then to get inductance of about 140uH you need about 1040 turns.

[Thomas]

http://coil32.net/online-calculators...alculator.html

[Friiman]

Thanks a lot, that gave me an idea to make the coil.
Nice finding someone who can answer this questions.
So now I will order som wire and see how it goes

[Friiman]

Think I was a bit unclear, the coils inner must be 9,7 or like 10mm because the ferrite rod is 9,7mm thick. Or am I thinking wrong, what would the winding be if the coils inner diameter is 10mm?

[kt315]

If coil inner diameter is 5.1mm (9.7 - (2.3+2.3) = 5.1) and wire gauge AWG32 (0.20mm),
then to get inductance of about 140uH you need about 1040 turns.

is the FERRITE rod diameter (only ferrite) 5 mm? i did calculate for 9.7.
i tell again - NOWHERE is a calculator for a coil with ferrite. you have to take 100uH approx value.

[Qiaozhi]

Try this ->
http://coil32.net/ferrite-rod-core-coil.html

[WM6]

Think I was a bit unclear, the coils inner must be 9,7 or like 10mm because the ferrite rod is 9,7mm thick. Or am I thinking wrong, what would the winding be if the coils inner diameter is 10mm?

My calculations was for air core coil.

In case of ferrite core there is no calculator as correct KT315 say, cause ferrite rods characteristic are uneven.

With ferrite you need other approach, by examination test, but you need inductance meter.

First you need to wound some testing turns of wire on your ferrite: say 30 turns or so (more turns more exact results at the end).

After testing coil (of say 30 turns) is wound, you need to measure its inductance.

If your testing coil of 30 turns has measured inductance of (say) 20uH, then you need per 1uH (30/20=1.5) 1.5 turns of wire.

According given results, you need for 140uH (140x1.5=210) 210 turns of wire (210 in this example approach of course).

[Noro]

This is photo of MD falcon test ,Friiman your coil is shelted in tinker cooper foil ? tnx for photo!

[Friiman]

This is photo of MD falcon test ,Friiman your coil is shelted in tinker cooper foil ? tnx for photo![ATTACH]34863[/ATTACH][ATTACH]34864[/ATTACH]

Yes Noro it's shelted in some copper foil. Is the pcb image of your md falcon design?
I have tested winding some coils and i am almost there with the count of winding.
Anybody know if a resistor in the pcb with a different tolerance will be a bad choice. I have tested resistors with 1% tolerance and 5% on the prototype pcb. What can be different with other tolerance?

[Noro]

Friiman you have a schematic? because i I suppose my schematic is wrong.Regard Noro.(
it does not fit for this forum schematic)

[Friiman]

Friiman you have a schematic? because i I suppose my schematic is wrong.Regard Noro.(
it does not fit for this forum schematic)[ATTACH]34865[/ATTACH]

I posted it earlier in this thread.

[Noro]

for example pin of 5 of ci 555 is free but in your schematic is galvanic coupled to colector Q5!
C5 33 micro in schematic is couple to ground, but in pcb is coupling to sensibiliti potentiometer

[Teleno]

The Falcon MD20 is extremely simple and depth is ridiculous, yet my first ever gold nugget was found using this device. It was on the slate bedrock of a ditch next to a primary deposit (gold-bearing arsenopyrite in quartz - Teleno peak - León - Spain).

Working principle: mineral or a metallic objects near the ferrite head change its inductance which causes a change in the amplitude of a Colpitt's oscillator. This kind of oscillator varies its amplitude with frequency. Metals increase the frequency and decrease the amplitude, minerals do the opposite. The waveform is then rectified and used to modulate a buzzer.

Because this machine has its well defined niche in locating superficial small gold and gold specks embedded in rock, I've decided to build my own version with the following (radical) modifications.

- Vackar oscillator at 400 MHz (amplitude is rather constant with frequency)
- Frequency counter based on ATtiny85.

It will work by continously measuring the frequency and comparing it to a sliding-window time-average. The MCU can be used to produce a sound indication (wavetable) and/or visual indication.

Will keep you posted.