Simplest PI detector possible?

[Harp]

bernte_one, I am very sorry, but not able to help.
First I made a PCB design, and then built a device to testboard to see how it works.
The unit is got started, but his performance was not satisfactorily to me (Eddy mentioned about 40cm for 2Euro!), so I gave up on making the PCB in acid ...
Elements from testboard I plucked out a long time ago.

In my PCB design, is only changed (simplified) a pulse circuit 555, but have retained similar characteristics of pulse, compared to the original.
See older post!

[bernte_one]

on the layout from me wa a mistake c8 1nf was not connected but i changed this yesterday before soldering
thats thats the one and only mistake i found

nobody else interested in the little pi
i cant imagine?

the parts on it are only some cents
and if it would work only for 20cm on a 1€ coin i would be enough

btw how can i fit an image so that veryone can see it as image and not as link

regards

[WM6]

Many interested, but waiting on your report.

[bernte_one]

i also wait for some reports
but if nobody else do it i am the one and only fool who burn his components and waste his time
i spend hours of layouting
see my first layout (half the size from actual layout) and the layout above
i spent a least 10hrs and materials for nothing
i know it should work somehow but something basicly is wrong there

so i will bring this to end - simplest but heaviest small detector last months
meanwhile i have more succes with µcontrolled units than with analog

[chemelec]

I built this up Last year, It did work but my test results were also NOT very Good.

[6666]

Post #72 #73 #75 have videos of working unit, I believe a 400uH coil works ok

[bernte_one]

thanks 6666,

have seen them, but thats far far away from at least 20cm for a coin or 40cm like sometimes said here

this detector should have much more pore when you quickly overwatch the pcb

[bernte_one]

i feels like nothing oscillate, which power should i measure on both coil pins and or on irf 740 pins

[geoscash1]

Tried twice...

I've built this twice with no luck... Something doesn't seem right with the schematic versus the pcb layout but I cant quite figure it out..
Anyone else mess with this? looks like something isn't right with the +/- rails on pcb versus the schematic but I am not very good with figuring these
out.. can anyone else look these over and see if there is something amiss?

[geoscash1]

my version with perf board

Below is my home brew version using perf board..it was a fun little project, but it would be nice if it worked...lol... I did use an mpsa13 in place of the bc547 (ordered some but never arrived) and a 390 damping resistor along with a 3k3 based on some of the comments and suggestions.. it should work but I have been looking and it seems something Is inverted but I'm not sure where.. I'll keep messin with it, If anyone spots the mistake let me know, I sure cant seem to figure out what's up with it...

[WM6]

Nice presentation geoscash1.

Did you check at which stage of circuit things go wrong? Did you check your board with scope? Par example what signal you get at pin 3 of 555 and at both end of C3?

[geoscash1]

Thanks WM6...

On power up the coil (open bundle wound) and the 740 get hot immediately so that is why I figure something is amiss with the power and neg rails or
reversed/inverted something.

I have went through it with a fine tooth comb and as you can see it is pretty easily traced out so all parts are correct and in the correct polarity. I spent a
little bit of time on it to make sure it was nice and layed out neatly just for the reason of quick trouble shooting. The scope I got awhile back has stopped working
so I don't have a way to check it other than a volt meter.

Do you have voltages and test points I can check with my meter? I need to make a pdf with test points and voltages for all the different boards, it would make a nice
go to reference and come in handy...

[Silver Dollar]

You can't get the simplest PI detector possible running? That's pretty bad! HeHe Just kidding!

You could disconnect the FET for troubleshooting. Heating of the FET and coil indicate too low
a resistance of the coil or to fast and wide a TX pulse. Not sure the design params but a lot
easier to check the 555 output with a scope. A meter on pin 3 should indicate a very low
voltage as it's the average. It looks like 100 to 1 and 60 ms pulse so a 60 ms pulse every
600 ms you should read 0.12v? (1 1/100 of 12V) (Just a guess)

Maybe your pulse is upside down. Did you swap the 100k and 1k timing resistors by chance?

[WM6]

I didn't make this detector, to say you proper voltage at partial test point.

You should go step by step. First check your signal generation stage. From memory IRF740 should be driven by 5v signal or above measured at gate or (in this case) pin3 of 555. For isolated check how your signal generator work you need to break connection between 740 gate and pin 3 of 555. Without proper instrument you can check 555 pin 3 output by simply connection earpiece between pin 3 and ground and listen signal. If signal generation stage work OK, then you can go to next step. Measure coil resistance too, it should be a little more than 1 Ohm.

[geoscash1]

You can't get the simplest PI detector possible running? That's pretty bad! HeHe Just kidding!

You could disconnect the FET for troubleshooting. Heating of the FET and coil indicate too low
a resistance of the coil or to fast and wide a TX pulse. Not sure the design params but a lot
easier to check the 555 output with a scope. A meter on pin 3 should indicate a very low
voltage as it's the average. It looks like 100 to 1 and 60 ms pulse so a 60 ms pulse every
600 ms you should read 0.12v? (1 1/100 of 12V) (Just a guess)

Maybe your pulse is upside down. Did you swap the 100k and 1k timing resistors by chance?

Silver Dollar, lol, that's what I thought to myself, if I cant get this working I need to retire...lol..
the 100 and 1k2 are original R's but some mentioned changing the 1k2 to a 2k2 or 3k3 for widening the pulse
so you may be right, I had placed a 3k3 in place of the 1k2. I'll swap that out today when I have time and recheck.

I really was shocked that it didn't work since it is supposed to be the simplest PI....lol...

That's what I get for being a rookie..

I need to get another scope (or get this one fixed), the one I bought awhile back was used but looked brand new and never
used or touched, 3 weeks after I bought it, it up and died on me...