PICKINI - an easy to build PI detector

[Dixix]

The procurement of the chip was a little difficult here. I could not order directly from FARNELL as a private person. Only through an intermediary. Had outrageously high shipping costs ......
But the construction of the PICKINI was worth it! Is a reliable small PI detector.
Also because I have improved the construction of my coils. I now use selfmade mixed graphite-varnish for the screen. This works very well. I highly recommend it!
Dixix

[Waikiki_Sweep]

Having same or similar detector on AVR (ATTiny84 or ATTiny85) should be wonderful. Chips are inexpensive and easy to find. Also you can buy USBASP programmer on eBay starting $2.82 with free shipping from China. Works great with FREE Khazama AVR Programmer software.

[joop]

Since the source code is available, it should be possible to port the code to AVR. The tough part of the porting would be to replace all of the specific PIC macro's like TRISA, CM2COM0, T1CON, etc, with AVR macro's.

[F117]

Dag Joop,

even tougher would be to port the internal resources used in the PIC, like e.g. the gateable 16 bit counter connected to the internal comparator...
No idea if something similar is available in AVR micro's ?

Best regards from Belgium,
- Bernard

[Waikiki_Sweep]

ATTiny84a mostly fits all requirements.

ATTiny84a has two counters one 8 and another 16 bits. The frequency of the
fast peripheral clock for the timers is 64 MHz (or 32 MHz in Low Speed Mode).
It has internal comparator.

ATTiny84a has 14 pins DIP case like PIC microcontroller used in the project.

The ATtiny24A/44A/84A provides the following features: 2K/4K/8K byte of In-System Programmable
Flash, 128/256/512 bytes EEPROM, 128/256/512 bytes SRAM, 12 general purpose I/O
lines, 32 general purpose working registers, an 8-bit Timer/Counter with two PWM channels, a
16-bit timer/counter with two PWM channels, Internal and External Interrupts, a 8-channel 10-bit
ADC, programmable gain stage (1x, 20x) for 12 differential ADC channel pairs, a programmable
Watchdog Timer with internal oscillator, internal calibrated oscillator, and four software selectable
power saving modes. http://www.atmel.com/Images/doc8006.pdf

[F117]

Sounds promising ! A timer running at 64 MHz would double the accuracy of the PIC controller at 32 MHz.
Is it possible to gate the clock input to the timer with the output of the comparator (the flyback pulse) ?
This would make all requirements complete.
If this is not the case: when the comparator output can generate an interrupt and you stop the timer at that point for a measurement, you will be very close !

I have never worked with ATtiny, so I'll leave it to the mored dedicated/specialized people to port the Pickini code to Atmel.

- Bernard

[joop]

Hoi Bernard,

Looks good! My experience with porting to AVR: it can be really tough. You will really need to dive into the datasheets.... But it is do-able. I currently have little time, sorry ;-)

[Waikiki_Sweep]

With using interrupts it looks absolutely doable.

Also TPIMD - Tiny Pulse Induction Metal Detector has beed described on geotech forum: http://www.geotech1.com/forums/showthread.php?17507-My-New-Pi-Metal-Detector-(ATTiny-25)
It based on the same principles (timer - comparator - interrupts) for ATTiny so big chunk of source code for ATTiny can be learned from here: http://www.miymd.com/index.php/projects/tpimd/
I love ATTiny84/85 but only started to use it. My programming experience limited to PHP only as web developer. Now I am trying to simplify classic Surf PI by using Attiny for timing and reading integrator output by ADC to make VCO sound. Without -5v Surf PI detector including preamp and integrator can be assembled with only two 8 pin chips (opa2350 and attiny85) also two transistors are needed to switch integrator inputs.

PICKINI is great project! I only have a question is it possible to keep comparator switching inside first 30 microsecond after pulse end to get small gold jewelry detected. With Surf PI sampling logic it works reliable.

[mohandes]

any body make this detector?
can give me more data for it
regards

[F117]

is it possible to keep comparator switching inside first 30 microsecond after pulse end to get small gold jewelry detected.

The comparator just makes a digital pulse of the flyback decay.
This pulse width is dependent on the coil used, + also limited by the single opamp amplifier. Dual opamps in cascade with less amplification are better for quick response.
The primary intention was to have a simple design that worked fine on the beach. It does, but the analog frontend can definitely be improved.
The internal comparator and timer is just used to give an accurate pulse width measurement - just like the Atmel based Tiny PI mentioned 2 posts before.

[Waikiki_Sweep]

Thanks for good explanation of how it works. Can you tell for the good coil what time you have in average from the end of 12V power pulse to "the point where the pulse is sliced inside the comparator" as you told, in microseconds. Is it something near 10, or 20, or 50 or 100, or 200 microseconds. Thank you.

[Dixix]

any body make this detector?
can give me more data for it
regards

Hello Mohandes
On this very nice website you will find all the information you need.

http://users.telenet.be/willaert/MD/..._en/intro.html

I built this PI detector. I highly recommend it. He works reliably. You can work with different coil / experiment.

My PCKINI:




I hope this information will help
Dixix

[Waikiki_Sweep]

Because of high power consumption (up to 100 mA) use of four 9V batteries probably turns to be costly. Also they are discharging too quick.
I can recommend replace it with five 18650 Li-Ion rechargeable batteries 3.7V each. ( 3.7 X 5 = 18.5 V ) or 21 Volt at full charge.
Also they will give you 2000-3000 mA/hour or 20-30 hours of work from one charge at full load.

If you have changed detector to work from 12 volts it is enough to use three cells because at full charge
it gives 4.2 Volts each or 3 X 4.2 = 12.6 V

You can buy 18650 cells for $1-2 each on eBay, you need $2-3 for holders for 5 cells. Charger for 2 cells costs near $3.
Also there are very good 18650 cells you will find if disassemble any broken battery from notebook, laptop, netbook computer.
Than you will have free and literally unlimited source of power for your PI detector. 500 charges for every cell.

[mohandes]

Hello Mohandes
On this very nice website you will find all the information you need.

http://users.telenet.be/willaert/MD/..._en/intro.html

I built this PI detector. I highly recommend it. He works reliably. You can work with different coil / experiment.

My PCKINI:

[ATTACH]27163[/ATTACH]
[ATTACH]27164[/ATTACH]

I hope this information will help
Dixix

thanks
max depth that you can find METAL ,what ??
my friend regards

[Legioner]

Because of high power consumption (up to 100 mA) use 9V batteries (or other battery as well) probably turns to be costly. I think better is if you have changed detector to work from 12 volts and buy sealed lead acid rechargeable battery for eg. APC (cost ca. £15 = $24.5). maybe this is wrong but... :-)