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

[bernte_one]

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

[bernte_one]

Hi Bernard,

one very important info:
it seems as a result of the coil memory function the detector will perform very bad after changing the coils
so one simple trick
after last activity with first coil switch detector off
then remove the batteries and turn the detector on
then switch it off put the batteries in and connect the new coil
then switch detector on
enjoy and dont get frustrated

and how often told, dont use indoor

[bernte_one]

sorry, i placed my question too fast, a fact that i could find by myself

[6666]

Can i use lm358 as replacement for lm318 ?

358 is duel op amp, 318 is single

[bernte_one]

Can i use lm358 as replacement for lm318 ?

[SWL]

Ok ... Thanks for the help

[BC547]

Removed all unnecessary ...

You could also remove R22 = 10 Ohm, another jumper.

R1 = 500 Ohm: make sure that this is at least 0.5W then - this is the reason why 2 x 1K in parallel was used.

[SWL]

Removed all unnecessary ... See it all right? If so, then I will do PCB... Thanks!

[BC547]

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:



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.

[Goaty]

@Bernard

“You could turn the sensitivity pot down until you get the error sound and then slightly up. This should be the least sensitive setting. If you really want to test it you should take it outside away from EMI.”

Hi Bernard,
Sorry about taking so long to get back to you but we’ve had a lot of other things going on around here.


I tried your suggestion again about moving away from interference but it still made no difference.
I can not fully stabilise it with any setting of the Sensitivity pot. It just gets frustratingly close at one point.


I’ve dragged out one of my original Pickinis to make comparative measurements of voltages and waveforms but got sidetracked making a light shield for the CRO to try to improve the quality of the screen shots.


I’m also still impatiently waiting for my order of SMD resistors to arrive from China. Tracking shows that it got to Aus around Christmas but there the trail goes cold. My guess is that it got held up/lost in Customs or by Australia Post. Of course, of all of the orders I made around the same time, the one I particularly need is the one that gets lost! It’s a good thing that I’m a patient person .



@FSB
I also puzzled over this but came to the conclusion that the extra resistor was used as a jumper for the single sided board layout. There is also a similar arrangement with R14 and R24 going to pin 3 of the opamp.

[SWL]

I realized ... I thought it was a special trick in the scheme)))

[waltr]

Hello dear F117! I read the whole topic, but did not find the information. My question is --- why is this done? Thanks!
[ATTACH]49112[/ATTACH]

Common method when one does not have the R values needed or wished to reduce the number of different values.
In this case wanted 20 Ohms but only had 10 Ohm resistor. So simply put two in series.

[SWL]

Hello dear F117! I read the whole topic, but did not find the information. My question is --- why is this done? Thanks!

[BC547]

@Goaty

but the range is very limited and still unstable

Maybe it is picking up a lot of indoor noise?
When I do measurements on the detector with the scope nearby, its backlight inverter introduces a lot of noise.
You could turn the sensitivity pot down until you get the error sound and then slightly up. This should be the least sensitive setting. If you really want to test it you should take it outside away from EMI.

@Boadil: All the best in 2020, including good health and great finds !

[Boadil]

happy new year, thanks for all F117