Anyone have Surf PI Pro Schematic?

[Comp]

AAgh!!! Bit stuck / disappointed today, no FET with the Postman, so at a loose end,.. I cant pot up my coils, or shield them, till I have tested them,.. and cant run up the board without a FET!!!! Tried my local Maplin Store, but they dont stock that one,... so thumb twiddling this weekend, it seems,....

On a plus note though, while I was in Maplins I spotted an item on offer, it is a heavy duty, plastic sand sifter in the MD section, reduced to just £1.99!!! (Part number N89KA)

Its an ill wind, as they say.....

http://www.maplin.co.uk/heavy-duty-p...-sifter-589991

Cheers all, Fred

[homefire]

Can't pop to the store and get one? Radio Shack may even have that one.

[Comp]

Nope, only local store is Maplin, & they dont stock,.. no worries, sure the wife can find me a few chores!!!!
(Actually, I reckon I have a few power transistors around here somewhere, I think I saw an early circuit using a TIP32 in this position,... will go look see if I have anything suitable,,,)

Cheers, Fred

[homefire]

Don't go there with the Power Transistor. It would change all sorts of stuff.

Coil Cap.

Coil Resistance.

Not to mention you would have to change Bias and stuff.

[Comp]

Ok, thanks for that,.... well, spent my evening 'surfin' sites,... {plus the odd glass of 'vino'}
ordered a roll of .50mm copper enamelled green wire, silver plated,... gonna wind the fastest coil I can!!! I have read a few comments on silver plated wire causing 'back eddy currents', and being the wrong choice, but I am a bit sceptical.... I know most electric current flows on the outside edge of a wire {skin effect}, especially at high AC {rf}, I know the signal is at a nominal audio frequency, but as the 'pulse' into the coil is rapid, it is in effect, RF, and am going to wind a 'basketweave' coil with this wire,......

http://www.ebay.co.uk/itm/180706971885

My belief is the more power you can get into the coil, the deeper the magnetic pulse,......

(although, I am not sure I want to be able to detect a 'Pepsi' can, at 5 meters!!!


Steer me right, if I am wrong, guys,....

Cheers, Fred

[homefire]

I too have heard silver conducts so well it hides the Currents.

Never tried it.

[Comp]

Ok, STILL waiting the FET from my kit supplier,... I have located a couple of IRF6215 P channel FETs locally,.. will these replace the IRF9640??? should I try one????

http://www.datasheetcatalog.org/data...rf/irf6215.pdf

It looks a slightly lower voltage rating,.. but I aint too sure on the rest of the specs,.. I have a 98% populated board here,.. plus 2 'test' coils, any help would be well grateful for, Guys,....



Thanks, Fred

[homefire]

Those would get you up and running but some things like the On resistance is twice that of the original.

May get warm on ya.

[mario]

Comp,

did you check the final inductance of that coil?

You're doing a beautiful job with that coil, I would hate to see you re-do it again.

Those nails should have added some further inductance, so don't be surprised if your final inductance is below spec.

[TH Jim]

Hi Comp,

I've been experimenting with different power transistors in surf pi and barracudas. Took the TIP127 out of the barracuda and put it in the surf pi and although the decay curve looked different on the scope and the damping resistor needed to be changed their was not really alot of difference in performance of the machine. Try these if you have them. Good luck,

Jim.

[golfnut]

On a PI, its my understanding that the coil is in steady state of current flow - the coil has a static mA or A flowing thru it prior to 'the pulse'
next,
The FET (conducting the current thru the coil) switches OFF, or , goes open circuit - very quickly. The magnetic flux that was around the coil (like an electromagnet) dies away very quickly.

It is this step change in magnetic field (from 'there' to 'not' there) that emanates away from the coil into the ground.


So my take on it is,
To get more initial magnetic field .... (more stored energy to unleash if you like) you can..

a)Reduce coil R is one way (like silver plated wire) = more amps, more stored field
b)Another way is a higher Supply rail (for the same Coil R) = more amps, more field
c)A bit of both..


So in essence just starting with a little more juice should give a 'bit' more depth.

Steve

[Comp]

Ok, thanks for all the above info, but I will settle for getting the board working, first!!!! LOL.
Still no FET in the post, so put the one I have available in. On a 12v supply, just over 50mA total board current being drawn,...and my hearingaid on 'loop' tells me the coil is radiating!!! I have set the 'offset' pot for 0V on the TP, and all other plus and minus supplies are present. If I trigger my scope from the pulse on the coil, I get the delayed pulse on the second 'scope channel, on the output of the Shmitt trigger, (pin 3 U4 ic, 4093B). Adjusting the 'Delay' pot, I can shift the output pulse along from 0 to about 60microsecs, {I have left it nominally at about 30 microsecs}, is this about right, to start with??. Altering the 'tune' pot doesn't seem to do anything, and there is no output from the speaker, other that a short [1/2 second] beep on initial power up, whilw waving a lump of metal across the loop. All cold checks' on passive components test ok, so have ordered some spare 358, 4066, & 4093B chips,.. looks like I am nearly there!!! Back to waiting for the postman!!

Mario, they are not nails in the coil, BTW, they are pencil lines on the coil former, and , Homefire, think the FET 'on' resistance of my replacement is half the original,.. nothing (apart from me!!! LOL) is getting overheated!!!!


OK Guys, thanks once again for all your input, and help,.. next episode of the saga shortly, Stay Tuned!!!

Cheers, Fred

[golfnut]

Fred I got the surf hexfets of ebay yesterday afternoon - They were delivered at 1pm today.

Semtech was the seller

http://www.ebay.co.uk/itm/IRF9640-Mo...item45fc0ab390

£1.25 each

steve

[Comp]

Thanks for that, ordered a couple,... I like to have spares of stuff I am fiddling with in stock,... {I have been known to pop the odd one or two!! LOL!!} Not sure if I am clumsy, or unlucky!!!

Cheers, Fred

[golfnut]

Yes I know what u mean. These fets are fairly tough.

Though saying that I reckon there is 6Amps going thru them when on...

FET is 0.5 ohm coil maybe 1.5 or 2 ohm on a 12v rail 6A

So make sure ur 555 is pulsing right or it will fry w/o heatsink..
S