Help with Surf PI waveforms/timing???

[golfnut]

Hi Fred, Spice is a simulator thats been areound for decades. Linear Tech bought the rights to it and its free in their website.
The file I did has the fet, coil etc , give it a try.

http://www.linear.com/designtools/software/

I use kitchen foil for my sheilds on an IGSL seems fine spiral wrap 4" wide 50% overlay

I think I got the necassary .net in here - get the simm set up.

double click the .asc file and it will go. Click simulate on the tool bar.

Then hover over any wire on the schematic and it will show Volts on that wire.



No that doesnt work either sim cant see the attached .net

S
Double click the coil symbol and it will show U the Coil current and the all important flyback pulse.

[Comp]

Hi, I have 4 boards to make up.. So Ive been reading around this one.

The commercial version .... sampling for target begins 20uS after the Vertical portion of the negative spike on coil.

You gate the level on this sample (which has not got back to zero if Target) along with the Delayed sample (the flat portion - after the main event) into the a Integrating Diff amp.

Essentially if there is an amplitude delta between the two sampling channels - your away!

Try modelling the FET coil etc in LTSPICE.

I have one I can post later (7:30pm) if you like and U can play with the variables..

I suspect 57uS ON time may not have saturated the coil flux to steady state? Opening this out may get more welly into - then OUT of UR coil.

Steve

Ok Steve, thanks for the input,...... not too sure what LTSPICE is, (some form of simulator??) not too hot with P.C.'s I'm afraid!! anyway, swapped R2 & R25 to 4.7K, this gives me a measured FET 'on' time of 80microsecs, and a sample window I can adjust down to 10 microsecs from the top of the knee.....results are not much different,.. so went back to basics, wound a new, plain coil, and seems a lot better.

I had wound two earlier, {plain, & 'basketweave'},potted in resin, and used copper self adhesive tape for the shield, and they seem to be the problem. I have put the copper tape tight to the coil, and I know read I should have left some space, (spiral wrap, or similar), between the two.

Now they are potted, bit difficult to alter!! LOL!! Never mind, all part of the learning curve.
I plan on a 22-24 turn, 10", 22SWG coil build tomorrow, and will test BEFORE potting!!

Cheers, Thanks for your help, Fred

[golfnut]

oops need a .net file too, where dya get that?

[golfnut]

ah needs a zip foler

[golfnut]

i do the up load, but doesnt appear what dya do to upload a spice file?

[golfnut]

sorry not great with attachments, take 2...

[golfnut]

see attached

Id estimate from the simulation graph te your Ts spike is borne of 1.8amps in the coil flyback. 12v rail in model 0.5ohm internal Res.

If you get the current going thru the coil for 300us that will give a squeak over 4A in the flyback pulse - the downside is the spike retun time is 100us rather than the 45us with 57us ON time

trade off.

[golfnut]

Hi, I have 4 boards to make up.. So Ive been reading around this one.

The commercial version .... sampling for target begins 20uS after the Vertical portion of the negative spike on coil.

You gate the level on this sample (which has not got back to zero if Target) along with the Delayed sample (the flat portion - after the main event) into the a Integrating Diff amp.

Essentially if there is an amplitude delta between the two sampling channels - your away!

Try modelling the FET coil etc in LTSPICE.

I have one I can post later (7:30pm) if you like and U can play with the variables..

I suspect 57uS ON time may not have saturated the coil flux to steady state? Opening this out may get more welly into - then OUT of UR coil.

Steve

[Comp]

Hiya!!! I would be grateful for that,... I have a range of Euro coins, (1 & 2 Euro, 10, 20 & 50 cents,....) plus a dollar bill,.. {dont think that will be too much help!!}. I had a little Aussie change from my trip to Perth, but cant seem to lay my hands on them, now,.. [Grandkids,.. :-) ]
Anyway, looking at the pics in this thread,...

http://www.geotech1.com/forums/showthread.php?t=18181

it seems to me that I should be able to get the sample pulse to start at some 20 microsecs or so, after the flyback pulse starts to rise, {If I have read his scope settings properly...} and I am WAY off that,. so looks like I will be playing around the Schmitt trigger circuit this afternoon.

Thanks for the help/input,

Cheers, Fred

[6666]

Hi Fred what coins do you have
I have some usa coins and 1 and 2 euro
and of course Aussie
will do some testing for you

also have a look at the output of the first amp there should be no ringing
maybe the damping R is not right

also I use 1 metre of rg58 to connect the coil
and of course do all your testing with the coil well away
from any other metal
my coils are simple random wind
and run it at 10.5 volts from a few nicads

[Comp]

Hi Guys, asking for help again!!!! I'm still struggling with my Surf PI 1.2 long board.It still seems low sensitivity to me,.. I have sorted out the R18 / R20 problem, (before that I could only detect a 2p to 2",... I can now spot it at 5" max... :-(

I've run a 'scope round a few points, trouble is, I dont know what should be where, (it is my first build, Guys!) I'll tell you what I have, & where, does anything seem out of order????

First off, the FET is running at roughly 615Hz, with an 'on' time of 57 microsecs,.. I guess this is about right??? Flyback pulse measures at 164V spike, which probably is not far off, either??

OK, the rise time seems fast, it gets back to 0V after 7 to 8 microsecs,... the sample pulse timing is adjustable with the delay pot, of course,.. the sample pulse on output of 14093 [pin 3, U4A] is about 40 microsecs wide, and the closest i can get it to the negative fall of the flyback pulse is 40 (ish) microsecs,... and the detector stops working when it gets closer than 42 Microsecs, or so.

does the above seem right??? I have tried a 390, 470, and 560 ohm damping resistor,.. coils ( I have wound 3) are a mix of straight coil, 22 turns, 10", 300 micro henry, and 'basketweave' types, same size, slightly less inductance. All give same sensitivity results. I have tried detector on a 12V Sealed lead acid 2Ah battery, and 2 different 11.1V Lipo's from my R/C heli's, same results.Can anyone with a Surf PI longboard tell me if any of the above are right, or wildy wrong????
Offset pot has set the opamp output at 0V, and 'tune' pot seems to do as it should, I set it to just start to 'burble' audio into the headphones....
I feel the sample is sampling a virtually 'flat' bit of the waveform, but is it because the sample is too late, or because the rise time is too fast, or are they about right, and I have a problem elsewhere???

TIA for any input, Cheers, Fred