TF-900_TM800

[Jose]

Very well Ivconic.

[ivconic]

Very well Ivconic.

[sinclairuser]

well done mate.

[ivconic]

well done mate.

[Qiaozhi]

It would be interesting if George could model the addition of the shorted TX loop. Specifying the resistance of the loop would be tricky ... skin effect would play a part.
I'm thinking the loop would behave like adding a parallel resistor across the 13mH/33nF combination,
example if the loop resistance = 100 mR, this would equate to 75 x 75 x 0.1 = 560R. on LC .
X_C = X_L = 690R, for comparison.

I tried adding a 4th inductor with L=1uH and a parallel resistor R=1mR.
Then changed the coupling coefficient to 0.85 and included L4.
There was then V=19.35mV rms across the aluminium rod (L4) with a current of 9.35A rms.
Does that sound reasonable?

[ivconic]

I used two green toroids. I measured two identical pieces of wire, the same length. Approximately 1.7m. And wound on toroids.
I didn't count exactly, I think there were about 65-70 windings. Both measures about 12.xx (closer to 13) mH. I wound 2x14 turns coils on the TX toroid. And that is that.
I had to switch to the "Slow motion" position. Due to the proximity of so many metal objects and "active" sources of interference.
Now I am waiting for 2 pairs of 3-pin connectors to arrive from the store.
In the meantime, I've done some mechanical work. On TX and RX pcb soldered good and "thick" coaxial cables with 2 internal leads and a very good copper shield.
I glued the scale to the box where it was.
I opened two holes on the sides for the connectors.
Refreshed all metal parts with black spray paint.
I have the impression that the device works well. I have had two TM-808s so far, one Gemini II and I can compare.
It will take me some time to draw the correct schematic from the pcb draft.
And there's a distinctive switch with 4 segments x 4 positions. Which is the same one found in many White's models.
The other day i obtained White's Coinmaster 5000 GEB/D with exactly the same type of switch.
BTW that CM5000 is the next on my bench to be serviced and retraced.
In a future copy, the switch should be replaced with a better solution.
I plan to replace the aluminum pipes with copper ones in a future copy.
Instead of screws, soldering these pipes will be easier and more reliable.
Instead of a square shape, I think a circular shape is better.
LCD and Atmega can come instead of a scale.
The Atmega can also control 4x4051 switches.
If I take out the battery test, as it is now, the number of switches decreases.
The PCB can be smaller, and therefore the control box.
etc

[Skippy]

"I plan to replace the aluminum pipes with copper ones in a future copy."
This will obviously make it heavier. But the loop resistance will be lower, too, which could end up loading the oscillator too much, I've no idea how much. The operating freq may drop, or worst-case it may not oscillate.
Calculating the loop resistance is not easy. I assume the aluminium is some structural-grade tube, not pure aluminium, so it will have an IACS conductivity of 35% to 40%. But your copper tube would presumably be some water or gas pipe ? not pure electrical-grade material, so it will have undefined IACS conductivity, possibly low, in the 85% range, typical for phosphorus-deoxidised copper tube.

"Instead of a square shape, I think a circular shape is better."
It will make no measurable difference to performance. It may be harder to manufacture, too. And when you put the detector down on the ground, it will fall over.

[ivconic]

"I plan to replace the aluminum pipes with copper ones in a future copy."
This will obviously make it heavier. But the loop resistance will be lower, too, which could end up loading the oscillator too much, I've no idea how much. The operating freq may drop, or worst-case it may not oscillate.
Calculating the loop resistance is not easy. I assume the aluminium is some structural-grade tube, not pure aluminium, so it will have an IACS conductivity of 35% to 40%. But your copper tube would presumably be some water or gas pipe ? not pure electrical-grade material, so it will have undefined IACS conductivity, possibly low, in the 85% range, typical for phosphorus-deoxidised copper tube.

"Instead of a square shape, I think a circular shape is better."
It will make no measurable difference to performance. It may be harder to manufacture, too. And when you put the detector down on the ground, it will fall over.

1) It can be compared, aluminum tube looop and copper tube loop. Yes, copper tube for gas, for airconditioners. There are various dimmeters and wall thickness. Thinner walls = lighter. Easy to bend and easy to solder. Worth to try and compare.
2) Never mind the fallig over, question is in "sqare/surface area" difference between circle and square. "Larger antenna" is if it is square one. But circle one is having better "propagation".
Those are just thoughts. I took exact measurements of each part of the assembly, I can replicate it 100% the same, if needed.

[zakari]

1) It can be compared, aluminum tube looop and copper tube loop. Yes, copper tube for gas, for airconditioners. There are various dimmeters and wall thickness. Thinner walls = lighter. Easy to bend and easy to solder. Worth to try and compare.
2) Never mind the fallig over, question is in "sqare/surface area" difference between circle and square. "Larger antenna" is if it is square one. But circle one is having better "propagation".
Those are just thoughts. I took exact measurements of each part of the assembly, I can replicate it 100% the same, if needed.

hi masters
can using this type coil for pi detector???

best regard
zakari

[Skippy]

"The question is in "square/surface area" difference between circle and square. "Larger antenna" is if it is square one"

Well obviously if you're changing from a 'square' to a circle, you're not going to make the circle the same diameter as the distance between opposite sides of the square, it would be undersize. But I don't think the circle should be the diameter of the diagonal of the square, either, that would be over-size. Somewhere 'halfway' between the two would be about right. Alternatively, make the circle have the same circumference as the 'rounded square'.

I doubt there would be any real-world difference between 'round' & 'rounded-square' simply because the targets you're wanting will be 80cm+ up to several metres from the coils, distant enough that any magnetic field irregularities caused by the square-ness will be undetectable.

I guess the real reason 'square' was used is related to ease-of-manufacture, and portability / packaging. The Fisher Gemini packs away like a rectangular box .. I suppose it would be a bit bigger if round coils were used in its manufacture.

If you are going to make a replica, what would be worth doing is making an optional smaller coil assembly, ( perhaps a bigger one is not needed ) , to fill in the performance 'gap' between what a conventional detector with a larger coil can achieve, and what the standard two-box does. Something like 65% of the original loop diameter, and spaced 65% of the distance apart.

I am unable to visualise how 'big' a two-box coil behaves. Something I planned on doing one day was a software/math model of a two-box coil. The resulting data should allow me to find an equivalent mono-coil diameter. Mono coils have easy maths, so make the best reference coil to compare with.

[Carl-NC]

The TM808 (and I assume the TF900) uses solid aluminum rods for the coils, not tubing. Copper tubing will especially be easy to damage.

[Carl-NC]

can using this type coil for pi detector???

Yes.

[Davor]

Resonant coils will be effectively larger than their physical dimensions. It is not easily modelled. But in any case, having a good Q should make it better.

[ivconic]

"The question is in "square/surface area" difference between circle and square. "Larger antenna" is if it is square one"

Well obviously if you're changing from a 'square' to a circle, you're not going to make the circle the same diameter as the distance between opposite sides of the square, it would be undersize. But I don't think the circle should be the diameter of the diagonal of the square, either, that would be over-size. Somewhere 'halfway' between the two would be about right. Alternatively, make the circle have the same circumference as the 'rounded square'.

I doubt there would be any real-world difference between 'round' & 'rounded-square' simply because the targets you're wanting will be 80cm+ up to several metres from the coils, distant enough that any magnetic field irregularities caused by the square-ness will be undetectable.

I guess the real reason 'square' was used is related to ease-of-manufacture, and portability / packaging. The Fisher Gemini packs away like a rectangular box .. I suppose it would be a bit bigger if round coils were used in its manufacture.

If you are going to make a replica, what would be worth doing is making an optional smaller coil assembly, ( perhaps a bigger one is not needed ) , to fill in the performance 'gap' between what a conventional detector with a larger coil can achieve, and what the standard two-box does. Something like 65% of the original loop diameter, and spaced 65% of the distance apart.

I am unable to visualise how 'big' a two-box coil behaves. Something I planned on doing one day was a software/math model of a two-box coil. The resulting data should allow me to find an equivalent mono-coil diameter. Mono coils have easy maths, so make the best reference coil to compare with.

That's a good thinking! I was asking myself the same.
When it comes to such an old design; I always see a challenge in some modification.
Mere replication, cloning ... I don't feel any challenge there, nor is it interesting to me.
In this case, I am most interested in the miniaturization of the whole assembly and pcb, some minor changes, for example around that mechanical switch,
which it is difficult to find in local shops.
Even what you mention, possibly reducing the size of the antenna.
But that it makes sense, just like you said: that it still has a depth better than I/B and most PIs, at least on large targets.
I mentioned CD4051 .. in fact here two CD4052 should replace the mechanical switch. I believe there are better solutions.

[ivconic]

The TM808 (and I assume the TF900) uses solid aluminum rods for the coils, not tubing. Copper tubing will especially be easy to damage.

Yes, the same at TF900 too.
...
I am not sure, I think those "copper" pipes for airconditioners are not of pure copper but some stronger alloy. Maybe I am wrong, I will have to ask about.
I am not against aluminum, at the end I will use it too, if other options turns to be bad.