Blacksand detector ? (titanomagnetite)

[Andi68]

Thank you very much Eric.
Is it worth building it after?


Andi

[Polymer]

There is no cable coiled around the shaft as the coax goes straight up inside the fibreglass shaft sections. In the picture it could be an interference pattern somehow caused by the compression I used to reduce the file size to a more manageable value for posting. Or possibly a degradation cause by re-posting?

Detector on the right is the one used on the beach. [ATTACH]50413[/ATTACH]

I have never had a problem with coiling a cable even around a metal shaft, provided it is coax. Coax has no external magnetic field to react with anything.

Eric.

Thank you for clarifying this Eric. Talk about optical illusions ... no pints imbibed during viewing ... but now.

Hmm, about coax not reacting to metal shafts. I have that situation though, but only when the delay is lower than 12ish us.

I can only guess that the conductor inside the coax is ever so slightly "detecting" the pole somewhat, being in such close proximity (a few cm) AND moving with each (slow) swing.
In my case the cable is swimming/movable in relation to the pole as the detector electronics are to my back on a belt around my waist.

[Ferric Toes]

Hmm, about coax not reacting to metal shafts. I have that situation though, but only when the delay is lower than 12ish us.

I can only guess that the conductor inside the coax is ever so slightly "detecting" the pole somewhat, being in such close proximity (a few cm) AND moving with each (slow) swing.
In my case the cable is swimming/movable in relation to the pole as the detector electronics are to my back on a belt around my waist.

I have had this effect too at short delays, but there is a different cause. Where the coax enters the coil shell through a strain relief cable gland, the coil is detecting the circular end of the coax braid. As the coil is scanned side to side, the braid will tighten and loosen slightly which gives a variable signal. The way I cured it was to add an extension piece to take the end of the coax further away from the coil winding. . Water drag on the cable makes the effect more noticeable when swimming than in air.

Eric.

[6666]

Your curiosity shall be satisfied. [ATTACH]50418[/ATTACH]

Eric.

Interesting circuit Eric, thanks.

[Andi68]

Maybe I'll try a replica in winter

[6666]

Your curiosity shall be satisfied. [ATTACH]50418[/ATTACH]

Eric.

Hello Eric, I built the 555 oscillator that feeds the 4017, using a 1000 Pf cap and I get about 12Khz on pin 3 does that sound about the right frequency or PPS ?

[Ferric Toes]

Hello Eric, I built the 555 oscillator that feeds the 4017, using a 1000 Pf cap and I get about 12Khz on pin 3 does that sound about the right frequency or PPS ?

Hi Bruce,
Something is amiss as on my unit I get 66kHz on pin 3 and 6.6k pulses per sec out of the decade counter. I'll check the timing components on my unit and see if they match the schematic I posted. At least three versions of this probe were made and maybe values changed. Mostly this circuit was used as security frisker and marketed by a company in that area of business. The security unit had a small truncated oval coil, while the pinpointer has a cylindrical ferrite cored coil.

No problems with anyone wanting to build it, but use something better than a 709 for a preamp. There is also a simple improvement when driving a piezo sounder which I will post later.

Eric.

[Skippy]

The piezo could be driven between the 555 timer pin3 and the transistor inverter, so it gets double the drive voltage ?
Step-up transformers are very effective at getting high outputs from piezo elements. They are widely used in siren / alarm equipment , such as smoke detectors and carbon monoxide alarms. I've worked with these alarms in a previous job. The transformers are simple ferrite bobbin based ones, with auto-transformer windings, 3 wires brought out. Amongst my scrap I have the guts of a 'Spiderwrap' security tag, used to protect 'big box' items in retail stores. The piezo element is very small, 12mm diameter, 5mm high, and the alarm is powered from a single 3V lithium coin cell, but it's pretty loud, because of the transformer drive.

Attached pic of the 12mm element + TX , and a 30mm siren + TX.

[Ferric Toes]

The piezo could be driven between the 555 timer pin3 and the transistor inverter, so it gets double the drive voltage ?
Step-up transformers are very effective at getting high outputs from piezo elements. They are widely used in siren / alarm equipment , such as smoke detectors and carbon monoxide alarms. I've worked with these alarms in a previous job. The transformers are simple ferrite bobbin based ones, with auto-transformer windings, 3 wires brought out. Amongst my scrap I have the guts of a 'Spiderwrap' security tag, used to protect 'big box' items in retail stores. The piezo element is very small, 12mm diameter, 5mm high, and the alarm is powered from a single 3V lithium coin cell, but it's pretty loud, because of the transformer drive.

Attached pic of the 12mm element + TX , and a 30mm siren + TX.

Here is the mod I used in a later version. The 47mH choke is inside a small ferrite housing and is about 10mm diameter and 10mm long. It has to be mounted at the far end of the case away from the search coil and at right angles to it as otherwise there is a bit of interference. Also quite loud.

[6666]

Your curiosity shall be satisfied. [ATTACH]50418[/ATTACH]

Eric.

For interest I found a small article about the simple 555 timer, second circuit down.
https://www.electronics-tutorials.ws...ts-part-1.html

[Andi68]

Dear Eric,


can you say something about the range of this Pi Pinpointer?


greetings

[Xtrem]

Where can i find this type of potentiometer ? very nice , complete sealed

[kt315]

Where can i find this type of potentiometer ? very nice , complete sealed

[ATTACH]50740[/ATTACH]

PLEASE read my opus BEFORE to make the pics. https://www.geotech1.com/forums/show...here-share-out
NOT SO HARD -! TO DO -!

[Xtrem]

Oh sorry , its not my pic , its from Eric.

[Ferric Toes]

PLEASE read my opus BEFORE to make the pics. https://www.geotech1.com/forums/show...here-share-out
NOT SO HARD -! TO DO -!

That picture was taken a long time ago with a early digital camera. Not Xtrem's fault. The picture is good enough to identify the component in question.

Eric.