Can pinpointer detecting thin chain?

[Polymer]

Forgot to answer the "overload" situation.

When metal touches the tip, my pinpointer squeals consistently after the beeping has gotten faster and faster when target getting closer.

So I dont have a "dropout" of the signal. If I remember right, the NUPI has several working points. It may have to do with this.

I like it this way. I then know I am "on top" of the target.

[Polymer]

Is this the one
https://www.geotech1.com/forums/show...205#post231205

Yes, thats the one!
You can leave out the 22uF capacitor parallel to the buzzer.
I have used the 68k Ohm resistor and a 10k Ohm pot for coarse adjustment with inbuilt power switch.
The fine adjustment is a simple 480 Ohm pot, no parallel resistor.

Your needed resistor adjustment values will vary with the 4024 ic used.

Its all mounted on simple strip-board.

Good Luck and enjoy!

I will be travelling and using this pinpointer intensively the next months. I will see how it holds up.

Quick photo of mine:

[6666]

I use PP capacitors for the 33nF & 1nF capacitors. It looks like all the box capacitors you are using are PE, they are smaller than the PP ones.
Instead of a ceramic for C4 I have used a PE capacitor. Not sure if these components make such a difference.

What definitely is very different, is the ferrite I now use.

Breadboarding and having the coil wires flopping around also makes it more unstable.
Cant find the file right now, I have been using a printout which has been in the box "to do" for years now.
See if you can find the schematic from Chemelec.

I know how frustrating and amazing the NUPI pinpointer is. Dont give up.

I will build another one the next few months and hope to achieve similar results hoping this one is not some random luckiness.

As you can see, I do not fully understand this myself yet.

The transistors I used are 2n3904 and 2n3906, nothing special.

Ha, the patent you posted is from Whites ... perhaps Carl might like to comment.

Is this the one

https://www.geotech1.com/forums/showthread.php?21373-Can-pinpointer-detecting-thin-chain&p=231205#post231205

[Polymer]

Good to hear it works for you. What type of components are you using to achieve such stability? My attempt which you can see a few posts above was drifting like crmelec.
I cant find the file azy, forcing me to scrap the project. Plus the overload problem, which I presume you don't experience?

Also I found UK patent GB2104660A from the 80s which seems to describe a similar circuit using the same oscillator and frequency divider. Maybe it could help someone understand the principles behind this pinpointer project.

I use PP capacitors for the 33nF & 1nF capacitors. It looks like all the box capacitors you are using are PE, they are smaller than the PP ones.
Instead of a ceramic for C4 I have used a PE capacitor. Not sure if these components make such a difference.

What definitely is very different, is the ferrite I now use.

Breadboarding and having the coil wires flopping around also makes it more unstable.
Cant find the file right now, I have been using a printout which has been in the box "to do" for years now.
See if you can find the schematic from Chemelec.

I know how frustrating and amazing the NUPI pinpointer is. Dont give up.

I will build another one the next few months and hope to achieve similar results hoping this one is not some random luckiness.

As you can see, I do not fully understand this myself yet.

The transistors I used are 2n3904 and 2n3906, nothing special.

Ha, the patent you posted is from Whites ... perhaps Carl might like to comment.

[Cazavor]

Good to hear it works for you. What type of components are you using to achieve such stability? My attempt which you can see a few posts above was drifting like crazy, forcing me to scrap the project. Plus the overload problem, which I presume you don't experience?

Also I found UK patent GB2104660A from the 80s which seems to describe a similar circuit using the same oscillator and frequency divider. Maybe it could help someone understand the principles behind this pinpointer project.

[Polymer]

Now that I have measuring equipment and more experience, I have revisited this project.
Made a new coil to the NUPI uH specs by measuring whilst using the Chemelec schematic.



This pinpointer runs extremely stable, compared to the ones I made before.
Running at ambient 35?C whilst lying in the sun and tested in the fridge at 4?C.
No more sensitivity to movement in the air when waving around (compass effect).


No more reaction to probing pressure in the ground.
Distance for a nickel is about 2 1/4 Inches.


Not as far as the previous ones with optimal bench conditions, but waaaay better out in the field.

No more constant adjustments of a finnicky little critter.


The ferrites I have used now are NOT from am radios.
They are from inductive welding. 5cm long x 9mm diameter in this case.


I have also NOT potted the ferrite coil in the pipe this time.
Its "suspended" in the pipe with two wound foam strips front and back of the ferrite.
So the ferrite is now mechanically decoupled from twisting, bending, pressing when probing.


Have also used proper pots instead of the tiny 10 turn ones this time.

[WM6]

Nice building process presentation.

[Cazavor]

Also attempting to make a NUPI pinpointer here, my progress so far has been:
- 8 mm x 160 mm "400НН" NiZn ferrite rod from Урал-112 radio
- cut into three 53 mm long pieces by filing a groove around the rod and snapping
- cores taped together with electrical tape
- first layer 104 turns of 0.32mm wire
- second layer 79 turns of 0.32mm wire = total 183 turns in L1 giving 1.56 mH
- third layer 100 turns of 0.32mm wire giving 0.42 mH, combined whole coil inductance 3.57 mH, coil finished
- wired up the NUPI FINAL 2014 circuit on the breadboard, with some changes due to available components:
LM2931-5.0 regulator for low dropout
TR2 is S9014
TR1 is S8550 with beta of 260
100k resistor in series with the pots to find the correct bias point which turned out to be 136.6k
C4 is 2.2 nF ceramic
C3 is 10 nF polypropylene
C1 is 1 nF polypropylene
C2 is 22 nF + 10 nF polypropylene in parallel
- nice sine wave on L1, frequency approx 15.3 kHz

Really impressed with the circuit considering the low amount of parts. The sound is very nice. The power consumption is just 1.2 mA with no metal around. But the PC buzzer takes 80 mA at full blast. That'd be 0.7W from a 9V battery! Sure doesn't sound like that. Must be possible to reduce. With loose balancing I detected 1 euro reliably from ~5 cm. With on the edge balancing more is possible, but I didn't bother yet due to higher instability/drift.

Also I checked on the scope that if I put a metal object closer to the coil the oscillator amplitude decreases and beeping starts. If I put a larger object really close, then the oscillator collapses and the sound stops completely. Any way around that?

[Carl-NC]

Bipolar Pulsing??

Current pulsed in both directions, using an H-bridge drive.

[Andi68]

Bipolar Pulsing??

[Carl-NC]

In the F-Pulse/TekPoint I used a 9x65mm ferrite rod, or something like that. With bipolar pulsing to cancel Earth field there is no compass effect at all. Probably will get similar results with monopolar pulsing and an EFE subtraction sample.

[Eddy71]

A long rod works well on a table if it is not moved in space.
I've seen errors when the rod moves up and down, right and left. The magnetic field of the earth has a strong effect on the long rod.

[walkman]

And when the rod rotates in space, isn't there an erroneous detector response?
(rod looks long)

Hi Eddy71,

I haven't seen such an error yet. I will continue the tests.

Ferrite rods 1cm diameter and 70mm long. L1=1,6mh L2=0,330uh

5,5 cm under the brick 1 coin detect.

[dbanner]

Northfinder pinpointer pro.

[Eddy71]

And when the rod rotates in space, isn't there an erroneous detector response?
(rod looks long)