PICKINI V3 - an easy to build PI detector

[bernte_one]

will post my pictures this evening

[6666]

some new 1 and 2 euro coins left behind after a sunny weekend at the beach: enough to buy a beer / ice cream

[Beenthereuk]

Just adding something to this. Having spent too much time trying to get this to work using a 330 uH coil with 20 T and failed because it kept becoming unstable, I have now gone up to 550 uH with 42 turns of 0.8 mm wire (R=1.4 ohm, 25 cm diameter). Current consumption now is between 55 and 75 mA and the circuit is stable.
Range in air to £1 UK coin is 20 cm.

[bernte_one]

Thanks for the info with the cool, but are You sure you habe 550µh with 42 turns?

[6666]

Calcs way bigger than 550uH.

[Beenthereuk]

OOps, yes you are right, it is almost exactly twice the 550u value at 1.18 mH - I must have quoted the value for one of the other coils I tried (tried many...) now remeasured using this: http://uk.farnell.com/jsp/displayPro...FQgYwwodTVoA4w

Everything else is the same. I've now hot glued it into its wooden base and will foil wrap and seal it the best I can. The lower running current means the MOSFET barely gets warm now and batteries should last longer.

[6666]

I've now hot glued it into its wooden base

Do you have any pictures to show us what you are doing ?

[Beenthereuk]

I'll record a video of it all next week - just finished the coil (grooved wooden base, coil, hot glue to keep it in its groove, aluminium wrap and gaffa tape - not 100% waterproof but will do for my first proper coil).
Ordered a suitable enclosure so should have it all finished by the end of next week.

[Beenthereuk]

Foil wrapping the coil seems to have cost me 5 cm in range to the £1 coin, making me wonder if it is worth it.
I just videoed it detecting the pound at between 13 and 15 cm. It used to pick it up at 20 cm. I'll try making other coils for it too.
Also noticed that it can barely detect a 10 pence piece even though it is larger than the £1 ?!
I'll upload pics and video later today.

[bernte_one]

just shield with some thin layers of graphit paint (graphit powder + clear laquer)

forget copper, lead or other metallic stuff which ist to thick

[Beenthereuk]

I made another coil (44 T, 880 uH, 2 ohms, 20 cm) from plastic coated 0.6 mm wire and just wrapped a few turns of earthed wire around it and that brought the range back up to around 18 cm. I'll post the video for that later too.

[Beenthereuk]

The videos screwed up (no sound) so will do them again tomorrow with another camera. I have some pics for now.

[Beenthereuk]

OK, here are the vids using both coils.

https://kcvmv-9fc.kxcdn.com/videos/95572.mp4

https://kcvmv-9fc.kxcdn.com/videos/95573.mp4

https://kcvmv-9fc.kxcdn.com/videos/95575.mp4

[6666]

OK, here are the vids using both coils.

https://kcvmv-9fc.kxcdn.com/videos/95572.mp4

https://kcvmv-9fc.kxcdn.com/videos/95573.mp4

https://kcvmv-9fc.kxcdn.com/videos/95575.mp4

Seems to be working ok, thanks.

[Beenthereuk]

Some minor mods to improve stability (it seemed that the op-amp's bias was affected by the MOSFET current pulse):
Make R10 47 Ohms instead of 10 ohms.
Add 100 nF capacitor from opamp pin 3 to ground.
Add 100 nF capacitor from opamp pin 8 to ground. I used ceramic.
Pulse width into pin 3 of the microcontroller using the 44 turn, 20 cm coil is 45 uS max.
Consistently getting 20 cm to a £ coin so I think I will make a 30 cm coil.

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