PICKINI V4 - an easy to build, self adjusting PI detector

[mohammadreza1100]

Hi andThank u bernard.please help me how to calibrate the v4?
Thank u.

[bernte_one]

hello nick,
i have to solder some wire to the external components, so i do some test and will see if the Problems appear too
as power source i use regulary 3 cells 18650,
for 100nf caps i dont use These 63v mks better choice are these film caps 100v
i will Show you some Pictures as soon as i finish
i hope we can solve it

[BC547]

what the push botton exactly do

The push-button is used for pinpointing.
When you press this button, the detector switches from motion mode, where it continuously keeps track of the average value of incoming samples, to non-motion where it keeps the last moving average value as reference. When you hear a beep while swinging, keep the coil away from this target, keep the button pushed en move it back over the target. You will hear a beep as long as it is hovering over the target, even when you keep the coil still. When you have accurately located the target by hovering over it, release the button again to switch to normal mode.
The pinpoint accuracy is the diameter of your coil. Unless it is really big, where you get a signal on one side and another on the other side.

If you replace the pushbutton by a switch, you will always work in non-motion mode. This does not take into account slow changes in the ground,eg, so you will have to switch back to motion mode now and again to take a new reference.

The normal mode is: if you use the pinpoint option, stuff the pushbutton. If you don't need it, don't connect the pushbutton. The default mode is motion. Only when you short the pushbutton connector to ground ( by pushing the normal open button) you will switch to non-motion mode.

[mohammadreza1100]

Thanks all
Thanks bernard
Thanks nick
my v4 finally works very good.only one question?what the push botton exactly do?for example when i detect the target if i push the botton what principle executed?if i use on/off switch instead push botton what will happen?
Thanks again.

[BC547]

.i don t understand because 2 weeks ago it works very well and suddenly this problem appear!

Battery voltage ?

[nick holas]

hi all
hi bernard
thank for you reply i do the right things during calibration phase.i don t understand because 2 weeks ago it works very well and suddenly this problem appear!!!
i will make some test ( i m very bussy in this moment at works grrrrrrrrr).it don t comes from my pcb because it works some weeks ago.

hi bernte i would say (yes it s not very clear in my frenchglish lol):when i switch on it detect the coil as good,and maybe 5 mn after when i switch it on again ,it don t recognize it as good coil at the same place!!!!
i don t know why perhaps a component is not enough strong or a component have warmed and i haven t see it ????
i ll try to change all transistor first then after i will see the other components (maybe lm31.
thank you twice

[bernte_one]

hello nick,

what did you mean when you write "once on tree" i´m not sure what you want to say

[BC547]

my pickini in DIP version don t work very good suddenly !!!!! once on tree it gives me false sound for coil and not very good deph(air test)!!!!!

Did you follow the proper procedure during the calibration phase after switch on: keep the coil away from metal / indoors EMI ?

Or: there might still be a problem with your new layout. Unfortunately I can't open your layout files under linux...

[BC547]

i buy the pickit 2 programmer.but the software did not support pic16f1824.when i check i found there is no puc16f2824 in the micro list.how i can update the micro list?

Have a look at the excellent post #128 in this thread by Eclipse.
He added the PIC16F1824 to the list of controllers supported by PicKit2.

[nick holas]

hi all
hi bernard
hi bernte
hi mohammadreza1100 you have to put in PICkit 2 v2.61 software the pic16f1824 in his list (you have to replace/add one file in the soft) so the soft can recognize pic16f1824 (i found the tuto in a forum .google it, it ll be easy)

bernard look what microchip has send to me today!!!!!!!!! (foto!!pic16f628 and pic16f1824) its very cool to them ,no?
now just need lm318 smd and ......... power!!!

my pickini in DIP version don t work very good suddenly !!!!! once on tree it gives me false sound for coil and not very good deph(air test)!!!!! +/-10cm for 2€ ( will try to make some test later)

[mohammadreza1100]

Hello bernard again.i buy the pickit 2 programmer.but the software did not support pic16f1824.when i check i found there is no puc16f2824 in the micro list.how i can update the micro list?
Best regard

[BC547]

The sensitiviy potmeter is typically 4K7.
I used one with built-in on/off switch, but you can implement separate potmeter and switch if you like.
The value is not so critical, it may also be 10K. You just need to apply a sensitivity voltage between 0-5V at the input of the PIC.

The tp.. points in the schematic are test pins.
tp1: flyback pulse at the output of the internal comparator ( digital pulse that will change width when targets are applied)
tp2: amplified flyback pulse going into the PIC
tp3: ground -- to attach an oscilloscope or multimeter ground clamp
You don't need to stuff any pieces of bare wire into these PCB holes if you are not going to use them. I use them for debugging.

[mohammadreza1100]

Hello bernard.i build the v4.pls say the value of sensitivity potentiometer and what is the usage of tp1 and tp2 and tp3?
Thank u.

[BC547]

I have no idea if this dual opamp stage will lead to more sensitivity with temporal sampling - as opposed to voltage sampling.

I now start by adjusting the DC level of the amplified flyback pulse measured 200micros after the pulse with the onboard 10bit ADC -- this is about where you would sample the voltage normally.
With successive approximationof the opamp DC offset, the output level is set to about 3.5 V.
I then apply the slice level for the comparator about 0.5V lower than this voltage.
The DC offset of the opamp is regulated with the onboard 8bit DAC. The slice level is obtained by filtering the PWM output.
For more sensitivity with temporal sampling, we can accumulate multiple samples taken over time.
With a single sample voltage detector, the only way to gain sensitivity is by increasing the gain ( I think, not being an analog expert ).
A couple of years ago, I tried the schematic you refer to with an LM358 and never got it to work properly. I was looking for a complete DC coupled front end that could be easily adjusted with a single 0-5V DC voltage.

With Pickini V4, the main disadvantage of the AC coupling is that each adjustment step on the DC offset voltage needs some time (2-3s) for the opamp output to settle again.

My personal wet dream is a single chip ( PIC) PI detector, with a direct coupled logic gate FET switching the coil, and using the internal PIC comparator as opamp. There are PICs who have onboard opamps but I think they are not fast enough for this application..

- Bernard

[bernte_one]

Hello Bernard,

can we improove the Performance from pickini
if we use the lm318 as dual stage amp ?

i made this simple mod at another pi detector and it results in 1/3 more sens to coin sized objects
i am not sure but i thhink the lm318 would work better as dual stage and with two additionel trimmers for Offset voltage
maybe i think wrong way

may somebody can try this ( with pickup pcb or so)

look at this dual op amp configuration

http://www.geotech1.com/forums/attachment.php?attachmentid=23505