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

[bernte_one]

Has someone a modified hex file with longer pulse width maybe set to 150?s or 200?s

but based on V4 with activated piezo output for pin7 of the pic controller
want to test bigger 1m square coil and big caps at the end stage, 3.300?f or 4.700?f

or Bernard maybe you can provide such a hex file version for a little donation

[BC547]

@Goaty:

The waveform should be between 0V and 5V as this is the input range of the analog comparator in the microcontroller.
The waveform is taken on pin 8/9 of the microcontroller.
In my pictures: 0V is at the bottom and 1V / div.
Your waveform looks too low-frequent. It should be a sharp spike, not a slope that takes about 500 microseconds to reach steady state again.
It should also have more amplitude. That is the reason why your sensitivity control is so limited.
Not much ideas left. Coupling capacitor C9 ?
Or disconnect the analog input of the microcontroller - remove R6 = 2K2 and measure the opamp output with the scope.
Opamp = LM318 ?

[Goaty]

Hi Bernard
Thanks for your response with some suggestions.


In answer to your comments -


“- it could be a very slow coil ? ( unlikely )”
This coil has worked OK with 3 or 4 other Pickinis


“- C10 over the opamp = 4.7 picoFarad ( NOT nanoFarad) ? You can safely remove this capacitor.”
I removed C10 and it made no difference. It was in fact a 5pF smd cap as I could not find my 4.7’s.
“- Damping resistor = 2 x 1K in parallel ? “
These are definitely correct.


My analogue scope was set set to 2v/div vert & 1mS/div horizontal. “0 V” was the centre horizontal axis shown in the photo. With your scope photos I am not sure where the “0V” X axis is as I am not familiar with digital scopes.


At this stage I have run out of ideas so I think I will put it aside for a while and concentrate on putting one of the other working full size boards into the new waterproof housing I have been building. If I wait too long the sea water will start to get too cold for diving. Today I took the empty housing to one of the local jettys and lowered it into about 2-3m of water for 20 min. It came up completely dry so all good so far – now to put some ‘works’ in it!


Thanks again for your help.

[BC547]

@Hammerhead : as Arionas illustrated: the 470 microFarad electrolytic capacitor does not need to be an aluminum housing.

@Goaty --- SMD build

Your waveform looks way too "slow" - too much damped - not high frequent enough, it should be a sharp flyback pulse.
The timebase on your scope is probably 1ms / division, - and vertically 5V / div ?

Something like this:



- it could be a very slow coil ? ( unlikely )
- C10 over the opamp = 4.7 picoFarad ( NOT nanoFarad) ? You can safely remove this capacitor.
- Damping resistor = 2 x 1K in parallel ?

[Arionas]

Hi Bernard I have watched your store I liked your offer at a reasonable price I want to buy the set But I want a favor from you Is it possible to replace irf740 + pc549 And put Instead of them Potmeter with on/off switch + The aluminum capacitor is not found in my country like them[ATTACH]49561[/ATTACH][ATTACH]49562[/ATTACH] And I will be grateful for your generosity

[BC547]

No problem. I will get back to you on Tuesday, as I am on holiday till then.

[Hammerhead]

Hi Bernard I have watched your store I liked your offer at a reasonable price I want to buy the set But I want a favor from you Is it possible to replace irf740 + pc549 And put Instead of them Potmeter with on/off switch + The aluminum capacitor is not found in my country like them And I will be grateful for your generosity

[Goaty]

The 10 Ohm resistors in the diagram R14, R24, R19 and R21 should be considered as jumpers on the single sided board and can be omitted.
@ Goaty: if you really want to make a 1 to 1 comparison with your original build, you should also program your SMD version with v4.0 or 4.1.
Which could be difficult now that the chip is soldered to the board...

Looking forward to some scope images.
My gut feeling still tells me that there is something wrong with your automatic DC offset adjustment of the opamp after startup: the circuit around Q3.
This should be reflected in your waveform. When you measure it at pin 8/9 of the PIC (TP2 in the schematic), it should look something like this:

[ATTACH]49117[/ATTACH]

The noise on this signal is mainly coming from the scope backlight converter ( together with other EMI sources in my garage... ).

The signal in this picture will give a valid sensitivity setting between 1.5 and about 4.5 V. ( = comparator slicing level to measure the flyback pulse width ).
Below and above these tresholds, you will hear the error tone ( no flyback detected at the comparator output ) - with firmware version 4.2
With firmware version 4.1, the slicing level is fixed at about 0.5V below the max flyback voltage.

When the offset is not properly adjusted, the signal may be clipped to 5V, giving a much smaller slicing level adjustment range and less sensitivity.
The closer you bring the slicing level to the top of the flyback ( the "widest" part ), the more sensitive the detector will be for small changes.
Too close => instability.

Hi Bernard


Sorry about the long time in replying but in the meantime I have completely remade the smd version on a new PCB with mostly new components (except pic). I also re-programmed another pic with V4.0 & tried it on the original pcb – all produced the same problem.


I have measured voltages and waveforms on the new board and sketched them on the attached pdf along with the scope waveform at TP2 – analogue scope set set to 2v/div vert & 1mS/div horizontal. The black voltages & waveforms are without the coil attached, the red with the coil.


I would appreciate if you could have a look at them and perhaps suggest what to try next. My feeling is that leakage in the electrolytics could be contributing but have yet to try swapping them for tantalum's. I also found that R2 (470R) had a tendency to overheat and go o/c so I replaced it with a normal 1/4W TH type



SMD Pickini.pdf

[BC547]

after some problems i thing it would better to remove this coils preset code lines, would cause less troubles

I understand your concern and you are right in a way that the calibration value ( = DC offset for the opamp ) that is stored in EEPROM may differ from one coil to another.
Actually, I never took this use case into account during the design, because I never change coils on the Pickini.
The main goal of storing the calibration values was to shorten the calibration time on the next startup.

If you are looking for a SW version that always starts the successive approximation from the middle value instead of the stored value, use this version:

http://users.telenet.be/willaert/MD/pickini/software/v4/Pickini4.0.hexhttp://users.telenet.be/willaert/MD/pickini/software/v4/Pickini4.0.hex

Calibration time may take a little longer but it will be coil independent.

[bernte_one]

Hi SWL,

do you manage to design new pcb without unnecessary parts

@all
please take my info serioues, if you have bad detection distance it can be possible that pickini try to start up with wrong coil presets
this can happen if you use different coils while testing and later when detecting

i can hear difference while start up sound
good coil / or stored coil found while startup a short double beep sound after some seconds from power on

bad coil / or not the one which is stored - it appears very light sound after startup procedure

after some problems i thing it would better to remove this coils preset code lines, would cause less troubles ?

[waltr]

OK thats clear, but i will do this way

https://reprap.org/forum/read.php?133,235148,page=1

Better alternative method for my 2,5w laser

Another Method is to use photo coated pcb and exposure the Isolation Tracks with laser but you still need the chemical For Photo prozessing (potassium... Pipe cleaner)

To burn black Paint is much easier und only needs one chemical to etch the uncoated Copper area

I like that method. Still get very clean and accurate lines but without the need for high power LASER.

[bernte_one]

OK thats clear, but i will do this way

https://reprap.org/forum/read.php?133,235148,page=1

Better alternative method for my 2,5w laser

Another Method is to use photo coated pcb and exposure the Isolation Tracks with laser but you still need the chemical For Photo prozessing (potassium... Pipe cleaner)

To burn black Paint is much easier und only needs one chemical to etch the uncoated Copper area

[ionut_mtb]

Probably due the the reflective nature of copper and copper's thermal conductivity.
Maybe if you give the copper a non-reflexive coating the LASER can transfer enough heat the cut the copper.


What power is that CO2 LASER?

130w

[waltr]

One friend of mine has a co2 laser from china and we tried to make pcb with it. I don?t know why, but did not worked. The beam is not cutting thru copper layer.

Probably due the the reflective nature of copper and copper's thermal conductivity.
Maybe if you give the copper a non-reflexive coating the LASER can transfer enough heat the cut the copper.


What power is that CO2 LASER?

[ionut_mtb]

has someone done the latest smd layout and can post it here?
i would like to do some pcb with laser engraver coming weekend and test my new software

One friend of mine has a co2 laser from china and we tried to make pcb with it. I don’t know why, but did not worked. The beam is not cutting thru copper layer.