My Pulse Oscillation detector project.

[BC547]

Nice design !
You can probably omit D2/D3 clipping diodes as they are already inside the PIC ?
I also have had problems in the past using the MCLR pin 4 as a pushbutton input. The controller would sometimes reset when holding the search coil near a damp grass surface. The solution is to add a 100nF to ground (in parallel with the pushbutton).

Best regards,
- Bernard

[joop]

Thanks for explaining...

[Aziz]

What I mean is the following:
Sampled Coil "bits": 000111100011100011110000111000.....
Reference "bits": 011100001111100001110000...
XOR: 011011101100000010000000...
Low-pass: 111111111100000000000000.. -> output (down mixed and filtered output beat frequency)

Very simple to implement and very effective. Can be implemented in an endless loop.
Aziz

[Aziz]

Note that Teemo has labelled pin 3 of the PIC as "RA4/C1IN1", which probably tells us that he's using the built-in comparator.

I'm not familiar with the PIC pins.
But I personally wouldn't use the comparator (IRQ).
The continious down mixing is simpler and faster.
Aziz

[Qiaozhi]

No, the ADC would be too slow. For the most of the time, the coil voltage would be at high levels and clipped therefore.

There is a 1 bit ADC implemented: lo/hi input line detection.
You can sample the bit very fast (just read the input line). Mix it with a reference nearby the resonance frequency. (The easiest and fastest mixer would be an exor operator).

Aziz

Note that Teemo has labelled pin 3 of the PIC as "RA4/C1IN1", which probably tells us that he's using the built-in comparator.

[Aziz]

ah, the clipping diodes, of course... But amplitude could still be measured after a time delay when amplitude is below the clipping voltage...

No, the ADC would be too slow. For the most of the time, the coil voltage would be at high levels and clipped therefore.

There is a 1 bit ADC implemented: lo/hi input line detection.
You can sample the bit very fast (just read the input line). Mix it with a reference nearby the resonance frequency. (The easiest and fastest mixer would be an exor operator).

Aziz

[joop]

ah, the clipping diodes, of course... But amplitude could still be measured after a time delay when amplitude is below the clipping voltage...

[Aziz]

So the search coil together with the 47nF capacitor form a resonant circuit which is excited by the FET. A change in amplitude is measured at the PIC input. A resonant PI?

No, you can't measure the amplitude as it will be clipped by the diodes. The coil induces a high voltage. It is typically driven at approx. resonance frequency of 77 kHz. The only way is to detect the frequency and mix it down by an internally reference (a simple xor) and put the mixed output to the piezo element.

I like it's simplicity.
Good work.
Aziz

[joop]

So the search coil together with the 47nF capacitor form a resonant circuit which is excited by the FET. A change in amplitude is measured at the PIC input. A resonant PI?

[Aziz]

Hi all,

according to the schematics and the processed information (debugging the hex code isn't necessary):
It is a BFO. (Or some kind of frequency shift detector.)
Aziz

[Aziz]

Hi
So here I try to post schematic, hex file and the new thing --partslist.

That's a mini TEM (tuned electro-mag.) transmitter.
Aziz

[Teemo]

Hi
So here I try to post schematic, hex file and the new thing --partslist.

[mickstv]

It doesn't open for me either.
The IP address is 212.47.211.148, but it doesn't respond to "ping".
Looks like the server is down.

Thanks Qiaozhi.

[Qiaozhi]

Thanks all for replays.
I guess I must change my web hosting provider.
Teemo

Please post the information here.
There is a Manage Attachments button further down the page when you make a new post or reply to an existing one.

[6666]

teemo
you can post files on here as attachments.