My Pulse Oscillation detector project.

[Teemo]

IRF730 may not to be the best MOSFET for the job. According to the datasheet it needs pretty high gate to source voltage. So it is probably limiting current.

[Teemo]

Hello!
Very good job AP! I't is good to see.

Do you consider that it is detecting ferrite, good or bad thing? In theory it should not detect ferrite core very well.
Regards,
Teemo

[ApBerg]

Hello,
Made the pcb, I did not have al the parts.......used a IRF730 , and some high volts diode and a 470 nf and 1000uF cap.
The coil is the red wire on a pvc tube with a ferrit from some 4 cm it in.
Sens for the coins some 3cm for the small gold coin and 5 cm for the large silver coin, the ferrit gives also some detection.

Nice as a pinpointer..?
...the ferrit core is also detected..!

Current was some 20 mA at 4.5 volts

Best regards

Ap

[satdaveuk]

Maybe with coil experiments you got a pinpointer, the component count is a plus

[joop]

Teemo's method, not as sensitive as a pure PI. But may be able discriminate,
since different metals will affect the ringing frequency and decay.

I was exactly thinking the same when I first saw this project. I think there is a lot of potential here...

[Teemo]

Thanks for the information. I didn't mean to degrade your project concerning the sensitivity.
You have a great project! It's an original and clean design. Maybe treasure hunting in your future?

Regards

Yeah, I feel treasure hunting can be fun. I will try it out next summer.

[Altra]

Thanks for the information. I didn't mean to degrade your project concerning the sensitivity.
You have a great project! It's an original and clean design. Maybe treasure hunting in your future?

Regards

[Teemo]

Working prototype with same firmware as published, can detect 10cent euro coin at about 5cm in air. Coil is 20 cm diameter, 27 turns of 0.75mm2 electrical installation wire on wood former, very robust, without shielding.
So it is not very sensitive, by treasure hunters standards, i guess. Still more like poor man's, ultra simple to build detector.
I can't do field tests outside this time of year, because of thick snow and cold weather. But i have scanned some logs for for hidden metal, for this it was perfect. This is why I got into this metal detector building the first place. Havn't done treasure hunting at all.
Teemo

[satdaveuk]

HelloTeemo,

Yes, it is a redrawn from your board in Sprint Layout. I like that drawing program.. it is easy to use.
A copy from an existing pcb is easy to make. If you have a 'copy.bmp' from a pcb board you can put that ‘pcb-bmp’ as an under layer in Sprint. Then it is easy to place components and draw tracks over that “ copy.bmp layer”.
When ready, to make a copy, the “copy.bmp layer” can be removed and so you have a “new” pcb that is free to modify and to adjust ....
Another reason I like Sprint is that on my Canon printer it makes very good transparency sheets, if I select in the “canon printer- options” : high resolution paper / best print quality /only gray... it gives a perfect transparent that is good to use with my modified UV face browner and “UV pcb” board.

Best regards and thanks again !

Ap

...no I have no connections to Abacom...!



I have not made the pcb... yet....so it may have errors!

Got to hand it to you ApeBerg, when it comes to circuit layouts and board placment/pcb, your the tops.
I also use sprint and have done since early days and as you say its a powerful yet not so difficult program to use with practice.
What I need to do is read the instructions to get full benefits of sprint.
Regards to all

[Altra]

Teemo,
Could you post some target depth measurments? With coins or other common objects.
What is the diameter of your coil?

Thanks

[Altra]

F117,

There is a complete project on this forum using your method.

http://www.geotech1.com/forums/forumdisplay.php?61-SPI-MX-3b

Teemo's method, not as sensitive as a pure PI. But may be able discriminate,
since different metals will affect the ringing frequency and decay.

[Teemo]

Hi Teemo,



Is there any advantage in measuring the total decay time of the oscillations instead of just measuring the decay time when the coil is damped with a resistor ?
I built a PI using the same pulse width measuring scheme, but without the oscillations and when you just accumulate enough periods ( pulses ) in timer1 (16 bit) you can get quite good sensitivity. Unless you get some extra information from the oscillating frequency ?

Best regards,
- Bernard

Good question!
I built some circuits with classic PI dumping resistor also. But i was not happy with the sensitivity of those. So I finally came up with this oscillating circuit.
Oscillating circuit is more sensitive in theory because from one current pulse(coil charging) we get about 40 oscillation periods, and during all those periods the changeing magnetic field at the coil influences the possible target. To be exact dumped coil has only half oscillation period. So osccilating circuit has potential to be 80 times more sensitive.
Teemo

[BC547]

Hi Teemo,

Timer 1 do not reach limit, it is started and stopped at every sine wave period that reaches over comparator treshold level, using PIC timer1 gate function. Download PIC12F1840 datasheet for details how this function works. Timer1 count is therefore proportional to the decay time.

Is there any advantage in measuring the total decay time of the oscillations instead of just measuring the decay time when the coil is damped with a resistor ?
I built a PI using the same pulse width measuring scheme, but without the oscillations and when you just accumulate enough periods ( pulses ) in timer1 (16 bit) you can get quite good sensitivity. Unless you get some extra information from the oscillating frequency ?

Best regards,
- Bernard

[Teemo]

Here is quick screen capture of my board layout:

[ApBerg]

HelloTeemo,

Yes, it is a redrawn from your board in Sprint Layout. I like that drawing program.. it is easy to use.
A copy from an existing pcb is easy to make. If you have a 'copy.bmp' from a pcb board you can put that ‘pcb-bmp’ as an under layer in Sprint. Then it is easy to place components and draw tracks over that “ copy.bmp layer”.
When ready, to make a copy, the “copy.bmp layer” can be removed and so you have a “new” pcb that is free to modify and to adjust ....
Another reason I like Sprint is that on my Canon printer it makes very good transparency sheets, if I select in the “canon printer- options” : high resolution paper / best print quality /only gray... it gives a perfect transparent that is good to use with my modified UV face browner and “UV pcb” board.

Best regards and thanks again !

Ap

...no I have no connections to Abacom...!



I have not made the pcb... yet....so it may have errors!