PICKINI V3 - an easy to build PI detector

[bernte_one]

some news?

did somebody made fotos or video from his finished build?

[BC547]

The time beween 2 pulses is 2 ms.
This influences the DC offset indeed. With a very slow pulse frequency, the offset resistor can be langer.

[Metalfree]

I have noticed that it is important to not only the pulse width but also the distance between a pulse and the other, must be nice contrast equal end up working must redo the calibration. That uses time between the two pulses?

[Metalfree]

The DC offset adjustment of the front-end opamp has nothing to do with the microcontroller that processes the flyback pulse.
Maybe the pulse that drives the FET is too short/long ? It should be around 100-120 microseconds.

It is not the problem with the PIC which I measure the pulse but op_amp, I have a pulse on the MOS 100US but I can adjust it until about 255, with R24 47k everything is adjusted well.

[BC547]

I'm trying this interesting metal, I can not calibrate the input voltage PIC. I use a program I wrote for a PIC18F25K22 in picbasic that I'm testing. The problem seems given by R24 4k7 replaced with 47k everything seems to work and you can adjust proper voltage 5.3 V.
It can be a writing error?

The DC offset adjustment of the front-end opamp has nothing to do with the microcontroller that processes the flyback pulse.
Maybe the pulse that drives the FET is too short/long ? It should be around 100-120 microseconds.

[Metalfree]

I'm trying this interesting metal, I can not calibrate the input voltage PIC. I use a program I wrote for a PIC18F25K22 in picbasic that I'm testing. The problem seems given by R24 4k7 replaced with 47k everything seems to work and you can adjust proper voltage 5.3 V.
It can be a writing error?

[Beenthereuk]

Given that the pin is configured as a digital output, a single BJT can be used to make a zero quiescent current, 0.25W amplifier for headphones that will be loud enough for anyone:



R2 and R3 are the headphones themselves. R1 and R4 are onboard. C1 should be removed / bypassed. And any small signal NPN transistor will do.

Use headphones with a built in volume control or insert a 100 Ohm variable resistor between the headphones and the transistor's collector.

[bernte_one]

The MOSFET runs hot though so I'll look for a heatsink.

better try some smaller coil wire diamter

[Beenthereuk]

if you can make a test with 0,4mm or 0,5mm wire

i often use yv wire 0,5mm and got best result with pi units

some energy must be burned on the coil, it is sometimes problematic if resistance of coil is too low

OK, thanks, will make a 0.5 mm wire coil too.

[Beenthereuk]

Got it back up to 5.25 V, running at 12 V & 165 mA, and it will detect the solder iron cleaning block at 50 cm.
Have also placed the connecting block back on the coil and it works the same once it settles down (detects it when placing it on).
The MOSFET runs hot though so I'll look for a heatsink.

[bernte_one]

if you can make a test with 0,4mm or 0,5mm wire

i often use yv wire 0,5mm and got best result with pi units

some energy must be burned on the coil, it is sometimes problematic if resistance of coil is too low

[Beenthereuk]

These work well. They have a 2 kOhm impedance and a digital output pin can source 20 mA+, so a 5/0.02 = 250 Ohm load can be driven directly.

http://uk.farnell.com/kingstate/kpeg006/receiver-piezo-leads/dp/1299873

I've even driven LEDs directly from the pins and they dont blow (they do have current limiting built in).
Must add min 100 nF supply decoupling close to the PICs VDD pin if driving heavy loads though or it may reset.

Regarding my Pickini, I removed the block and soldered the wires directly with the same result.
I then retuned the bias voltage to 4.75 V and managed to detect some mild steel at over 30 cm, with the circuit remaining quiet between sweeps.

I am using fairly thick wire for the coil (0.8 mm diameter) and am wondering if this is the reason my operating current, when the thing actually works, is so high (~160 mA).

What gauge wire do you all use?

[bernte_one]

hello piezo directly to output from pic controller does not work for me

if you replace the resistors in series from output to audio connector with a wire bridge the hole thing gots nervous

best results i got with simple headphone like bernard says already

or if you wish speakers add a external audio amp
than you have the possibility to adjust the outout

i think my final version has an amp and headphones

the most speakers i tested tend to get unstable when amp is full powered
or are not loud enough directly connected to µC

much succes

[Beenthereuk]

Thanks for the replies. sinclairuser: Yes, I was wondering about the connecting block and will remove it now and try again.
If it is that sensitive, will it not detect the wires leading away from the coil too ?!

Will also set the reference voltage at 13.5V Vdd but I do not think that is the problem. Current consumption is related to that voltage because I have had it operating at 160 mA and tuned it down to 120 mA before that video. OK, a 25 s delay on the battery voltage alarm does explain why I haven't heard it.

Bernard, yes, I always use it first too - it gives a good signal on just about any metal detecting circuit, regardless of how crap it is
The red thing is another 12F1840 pre-programmed chip that I promised a friend who I will be visiting in Greece soon (they have problems sourcing parts out there... third world countries.. nice beaches though!) - as I'm taking the detector with me, I've taped it to the large capacitor on the board so I dont forget it.

For audio, I tend to wire a piezo speaker straight on the output pin of a PIC - with 5V pulses, they are very loud. Just using the speaker as I dont want to **** those in the offices next door off.

[sinclairuser]

hi been there uk, your coil connector could cause falses, i used those block connectors on the first pi coil i made, and it detected it, it falsed like hell, when i removed it and soldered the wires it stopped, i dont know if it detects the brass or the steel screw but my first pi saw it.