DIY PIC12F1840 microcontroller based metal detector project.

		Quote:			Posted by {author}
	I did build a pin-pointer some time ago for a mate using a PIC (16f690), a few external components, a ferrite rod and I think 70 turns of 0.5mm wire (magnet wire) the depth was around 120mm for a 303 cartridge but he did locate a silver coin at 70mm. What has turned me off this design was the interference that we were getting in the VLF machine there was even an interference in my PI machine. What I did was to have all the timing on ADC so that I could change the timing according to the coil that I had (Based on previous experience)  By doing it this way I could fine tune it all and then ended up with a pin-pointer of reasonable ground penetration. The pin-pointer worked rather well as the field is well directed by the ferrite rod being surrounded by the coil but like I said before the interference (Possibly I could have done some good shielding) made it a pain in the butt  Grin I will try to find the schematics and source code for it as it was on my old PC (I still have it and love it) I do not have it with me, I use it in my lab to do all sorts of nutty things that I would not try with this one.

Hi Xavier,
I'm interested to see your schematic and code.
Teemo

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Hello everybody.

I did some improvements to the code. New version available at my

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Added 10 lines of code.
It should improve ground balance, and sensitivity to non ferro metallic, but it is just a proof of concept stage. Have not done much testing, and fine tuning to that jet. The idea that came just today to me.
Now it is using oscillation frequency information also.

Best wishes,
Teemo

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Hi Xavier,
This is nice prototype board on your picture.
How do you generate sound with pic? Is it same beeb/no beep solution as mine?
I have been thinking about programming some kind of variable frequency, multi frequency or variable volume sound. I ran out of timers in 12F1840 already, but it might be possible to figure something out. To use isochronous loops for example. Or to start a new project with some other chip that have more timers, like 16F1827.

The problem with beep/no beep solution is, that it cant take any advantage of human perception.

Everybody else are welcome to share their experience of PIC sound generation programming also.

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		Quote:			Posted by GoldDigger1950
	TO paraphrase the statement in Jaws, "We need a bigger PIC!"

Yes, but only a little bit bigger. I like those small PIC-s. And the way all the timing can be done in cpu cycle level in assembler.

		Quote:			Posted by GoldDigger1950
	Just remember that using the PIC method will slow down everything. Your tone might be generated when the coil has moved half an inch making pinpointing difficult. The analog way is much faster so consider a VCO.

The reaction speed is definetly the one thing to consider. But PIC itself do not limit the speed, unless we use very slow filter algorithms, which we do not.

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		Quote:			Posted by Teemo
	How do you generate sound with pic? Is it same beeb/no beep solution as mine?

As you can see on the prototype there are two Op-amps they are on the receiver side of the detector so effectively only the timing is done by the PIC there are three timers the first is the on time to charge up the coil then there is the off with a delay next is another on time, this on time is the analysis time in other words the coil is now on but in the listening mode to the Op-amps then the coil is turned off again and goes back into the charge time to start the cycle again. Like I said to you a few posts ago the timing is critical to have it working properly. The Op-amps then turn on a transistor that in turn turn on the buzzer and LED should there be metal in proximity. Before you ask the Op-amps that I used are TL071 and UA741 for the secondary amp I need to toy with it more but until my VLF project is complete I will not be doing any work on it. The good news are that the VLF is almost complete.       

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Xavier