My Pulse Oscillation detector project.

[waltr]

I built this circuit as a pin pointer using a ferrite rod out of an old AM transistor radio. Wound 80 turn #24 enamel wire of ferrite rod.
Used the PIC12F1840 processor and the 1.80 source code. I did change the default 'mode' from 0 to 1 since this is the mode I found most useful as a pin pointer.
This circuit/PIC code works great and makes finding a target in the ground much easier.

I didn't have enough good NiCad or NiMH batteries and could not get it working with 3-AA alkaline batteries so added a 7805, TO220 regulator to run from a 2-cell LiPo (7.4V Nom). The circuit works BUT the quiescent current of the 7805 is quite high and will discharge a 1000mA-hr LiPo in a few days. This defeats the idea of putting the PIC into Sleep mode and required adding an ON/OFF switch. There are newer 7805 like regulators with much lower quiescent current so this may still work.

First picture show the circuit prototyped on a plug-board and ferrite rod.. The large 2200uF cap is REQUIRED, else the PIC keeps resetting due to Voltage drop-out.
Next pictures show the project and the point to point wired perf-board in a plastic enclosure. The ferrite rod is inside the plastic Cigar tube which is attached to the box with two screws. This makes a handy pin-pointer as the rounded cigar tube is easy to poke around in the dirt to find the target.

[Spyke]

Can you post the code changed to mod1 at startup?
Or can you tell me how to do the change?

Marc

[waltr]

Can you post the code changed to mod1 at startup?
Or can you tell me how to do the change?

Marc

Simply change the DEFAULT mode value. Then re-build to produce a new hex file and program into the 12F1840.

        ;--------------initial MODE selection-----------------
        banksel MainState1
        movlw   .1      ;default mode

        movwf   MainState1

[fekemil]

I modified the code for the 12F1840 PIC, now default Mainmode0 is distance indication.
I use this circuit as a pinpointer. Coil is D=0,75mm enamelled copper wire, 30 turns, 0,6 Ohm, 175 mH. The body is made from drain pipe, bottle neck and cap. The head is changeable. I tried with bigger searching head, but not the best for treasure hunting without discrimination. Teemo wrote: "Ferromagnetic metal target objects decrease free oscillation frequency and non-magnetic metals increase oscillation frequency" So, when the program compare the result with the reference, and the frequency is decreasing, that means the metal is ferromagnetic, and it gives a high tone output. I tried modify this part and mute this sound, but no luck. I'm not a programmer.

[waltr]

Nice build. What is the diameter of the coil?
How well does this work pin pointing in a dug hole?

The code for the 1840 is pretty complex so not easy to understand and modify.

[6666]

so I bought a PICKIT3 programmer. PICKIT 3 already supports 12F1840, but in the MPLAB IPE only the low voltage version, PIC12LF1840 can be selected.

I use MPLAB IDE 8.76 and Pickit3 and have no problem programming a 12f1840, see post #78

[fekemil]

The diameter of the coil is about 125 mm, I used DVD cake box as a form. I have good results, but only in my garden, because in my country treasure hunting almost impossible legally. Even in my garden is illegal... I think this pinpointer very accurate in soil.

[fekemil]

I had old version of MPLAB IDE, today I have no problem with the new version. (After the stupid password-for-advaced-settings)

[waltr]

The diameter of the coil is about 125 mm, I used DVD cake box as a form. I have good results, but only in my garden, because in my country treasure hunting almost impossible legally. Even in my garden is illegal... I think this pinpointer very accurate in soil.

Ok. A shame its illegal. My grandparents came from Hungry in the early 1900's.

[reptooyep]

Hi every one.
I'm making my son's first detectorand this circuit seems simple and tiny enough for a light rod detector.
I'm having troubles with coil. I've tested a 25 turns of 0.15mm coil and had a poor depth (about 5 cms for 1€).
Then, i've tested a spider coil with 0.5 mm copper wire and have a better depth but not so good comparing to other detector i made before (10cm for 1€).
I then made a simple coil with 20 turns of 0.5mm copper wire and have no functionning at all. I think my powr supply is quite light for this 0.5 ohm coil.
When adding a serial 1ohm resistor, it turns on but no detection.
Is there any adjustments on componment value to fit the coil ?
The sound is also VERY VERY low. It lacks a transistor to power a speaker. I'll do this tonight.

[waltr]

reptooyep
Did you read through this entire thread?
The one observation is lack of depth compared to other MDs (PI or VLF).
What are the coil diameters?

It should not be too sensitive to coil but the high value cap, 1000uF, is a must and is best connected close to the MOSFET/Coil.

The piezo speaker is not loud at all. An audio amp is needed to drive a speaker.

[reptooyep]

First, thanks for your reply.
I read all thread quickly ... Maybe too much
My coil is 20cm circle.
I've put a BC 547 to drive the piezzo. It's a bit louder.
I've made several test with the parallel capacitor and get not so bad results
with 80nF instead of 47nF.
I wanted to use a 5v power bank but the one i have is not good.
I'll do the same as i always do : a 18650 battery with a dc to dc converter. I'll post results tomorow.
I have about 15cms for coin so, not so bad for a homemade kid toy.

[reptooyep]

Here is the air test with a 20cm spider coil (350uH).
The pitch becomes lower when a coin comes close to the coil, it should be higher ???
https://youtu.be/S2-BtTLF2VQ

[waltr]

Here is the air test with a 20cm spider coil (350uH).
The pitch becomes lower when a coin comes close to the coil, it should be higher ???

non-ferrous object produces a Lower tone.
Ferrous a higher tone.

Try an iron/steel object then copper, brass, aluminum, lead objects.

[reptooyep]

Oh, strange, i did not noticed any pitch difference with differents objects.
I'll test tomorow.
I have another coil to test with (the one from the video is the one from the right,
Tomorow, i'll test the other one