My Pulse Oscillation detector project.

[Qiaozhi]

Hi Qiaozhi.
Some points you got right some not.
1. RA5 pings the mosfet and resonance fereq. 77kHz is correct. But resulting decaying sine wave is not clamped. Clamped is signal that reaches PIC through R4, and to supply rails, between 0V and 5V
2. correct
3. correct, and comparator output drives timer 1 gate function
4. no, 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.
5. output audio is not pwm, it is just beep or no beep.

So it do not measure the ferequency for detecting metal, only the decay time.

Aziz, you are getting it way too complicated.
Here is link for PIC1840 datasheet
See timer1 Gate function
http://ww1.microchip.com/downloads/e...Doc/41441B.pdf

Also my block diagram on my web:http://www.digiwood.ee/images/metal_...matic_copy.png

So I was reasonably close, but got a little bit of the detail wrong.

The timer1 gate function of the PIC12F1840 seems really useful. By setting the T1GSS bits of the T1GCON register to "10", it uses the comparator as the gate source. Pretty neat!

Also, from your block diagram, I can see that you're using the internal DAC to generate the threshold level for the comparator. Presumably the user is not able to set the threshold level manually, so how is this controlled? Is this a self=adjusting threshold (SAT)?

Lastly, what is the sensitivity of this detector?

[Teemo]

Assembler source code!

Hello!

Thank you all for keeping up good conversation.

Today I released the source assembler code. Many people here seem to have pretty good knowledge of PIC programming. So it may happen that together we can improve from my original design to even further.

I encourage you to share your modification and test results, in case you decide to build this project.

Here is the link to my firmware page, there is also basic flow diagram:firmware-page
Direct link to assembler file:metaldetector100.asm

I also add zipped asm file here as attachment.

Best wishes,
Teemo

[joop]

Thanks, really appreciated!

[ApBerg]

Hello Teemo

Thanks for the info, it is a nice little circuit !

Next is some time to etch a pcb..

Best regards.

Ap

[Teemo]

Hi ApBerg
I see you have redrawn the board. Nice! What software did you use?
I made the board in kicad. I can share kicad files also. But I have no time tonight. I must investigate first what files and libraries I must include.

[6666]

Good job Ap on pcb

[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!

[Teemo]

Here is quick screen capture of my board layout:

[F117]

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]

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

[Altra]

F117,

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

http://www.geotech1.com/forums/forum...p?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.

[Altra]

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

Thanks

[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

[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

[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