Simplest PI detector possible?

[Watanabe]

I make some little modifications.
LS1 and pad (next in buzzer) are for earphone links.


Please, check.
Thanks.
;-)

[ATTACH=CONFIG]23156[/ATTACH][ATTACH=CONFIG]23157[/ATTACH][ATTACH=CONFIG]23158[/ATTACH]

Don't work.
Q3 (use IRF9640) very hot; (L1 = 0,345mH)
Work in the circuit today.
Somebody suggestion??

[mickstv]

Don't work.
Q3 (use IRF9640) very hot; (L1 = 0,345mH)
Work in the circuit today.
Somebody suggestion??

The IRF9640 is a Pch Mosfet, Looking at your board layout you actually need a Nch Mosfet i.e. IRF840, IRF740 etc.

[mikebg]

VHF RINGING !

Don't work.
Q3 (use IRF9640) very hot; (L1 = 0,345mH)
Work in the circuit today.
Somebody suggestion??

Watanabe, your design generates VHF ringing because stray capacitances and MOSFET form an oscillating circuit. Place an FM radio nearby to hear it.
To avoid this, you should connect a resistor 22R in gate lead of T2 (if there is no resistor R5). Note that T1 also needs two correct designed resistors (10k connected to its basis lead).

[Watanabe]

Thanks mickstv and mikebg.
My circuit works, but there is no way to 8 inches.
Pliers, can detect about 4cm.
A coin, lean on the coil.
My coil has 12cm (diameter) 4.5 ohm and 0.586 mH.


What characteristics of the coil with better performance?


thank you

[6666]

Mikebg
where are you measuring the VHF ringing ?
my CRO only goes to 25 MHZ.

[mikebg]

. Place an FM radio nearby to hear it.
To avoid this, you should connect a resistor 22R in gate lead of T2 (if there is no resistor R5). Note that T1 also needs two correct designed resistors (10k connected to its basis lead).

Simply hear the FM radio.

[Watanabe]

Working, but without great results.
Perhaps a good project for Pinpointer (with an appropriate coil).
To detect a coin to 8 inches, have a lot to learn.
Any suggestions?
Thank you.

...

[brucester]

Thanks for the video.

Not sure why you are getting poor results. I get better distance from using a coil half the size. What unductance is your coil? I first tried one with a 200uH coil and got no results. Doubled it to 400uH and it started working.

[Brazilian]

Working, but without great results.
Perhaps a good project for Pinpointer (with an appropriate coil).
To detect a coin to 8 inches, have a lot to learn.
Any suggestions?
Thank you.

...

Hi
Consumption can be high frequencies, or long pulse..

[brucester]

I think this is around 72Herts with 50% duty cycle.

I changed it to 100 hertz with only 100us pulses with arduino, consumes less and works better.

[Watanabe]

Thanks for the video.

Not sure why you are getting poor results. I get better distance from using a coil half the size. What unductance is your coil? I first tried one with a 200uH coil and got no results. Doubled it to 400uH and it started working.

I used 3 coils:
626uH; 30turns ; 26AWG ; 25cm(diameter) ; 3,7 ohm
419uH ; 25turns ; 26AWG ; 25cm(diameter) ; 3,0 ohm
362uH; 23turns ; 26AWG ; 25cm(diameter) ; 2,9ohm
For all similar results , and high current consumer (>220mA).
Thanks.

[Watanabe]

I think this is around 72Herts with 50% duty cycle.

I changed it to 100 hertz with only 100us pulses with arduino, consumes less and works better.

Wich coil characteristics ?? (AWG wire; turns; ohm; uH; diameter)
Thanks

[brucester]

Wich coil characteristics ?? (AWG wire; turns; ohm; uH; diameter)
Thanks

??

The pulse rate is set by the 555 timer and the relative resistors and capacitors.

I removed the 555 and pulsed the transistor with microchip thereby changing the frequency and width of the pulses.

[Eddy71]

Working, but without great results.

Tune R2 and R7 for best result (wery depending from coil unductance).

and high current consumer (>220mA).

Schematic curent about 60-80mA from 12V battery.

[Watanabe]

??

The pulse rate is set by the 555 timer and the relative resistors and capacitors.

I removed the 555 and pulsed the transistor with microchip thereby changing the frequency and width of the pulses.

Characterístics coil which you're using?

Tune R2 and R7 for best result (wery depending from coil unductance).
Schematic curent about 60-80mA from 12V battery.

Could you indicate the values for a better functioning?
(Included coil specifications that are using).

Thanks All