pi coil connections

[taliesin]

in different pi designs some coils are connected to v+ like in the hammerhead and to v- in the surfmaster.whats the consensus on which is best ?

[homefire]

LOL! What's best ? PNP or NPN transistors both do the job.

Just depends on how you do the job!

[taliesin]

if the coil is connected to ground and the sheild is connected to ground might the capacitance be less ?

[taliesin]

LOL! What's best ? PNP or NPN transistors both do the job.

Just depends on how you do the job!

hey homefire .quit with the LOL .it's a valid question

[homefire]

Sorry! I don't see that it would make any difference. Neg or Pos ground it's all the same.

How would it effect the C ?


Now that's funny!

[taliesin]

any shield is gonna add some capacitance .yes ? no ?

[homefire]

The shield just diverts the EMI and Ground Cap away from the signal on the coil.

Pos or Neg it keeps the receive signal a bit cleaner.

The shield it's self adds a bit of Cap to the coil but the Benefits out weigh the bad.

Does that make sense?

[taliesin]

have a read homefire http://www.irf.com/technical-info/appnotes/an-940.pdf

[homefire]

I see there talking about Grounded Load, but can't find anything about Capacitance problems.

????

[taliesin]

I see there talking about Grounded Load, but can't find anything about Capacitance problems.

????

you'll agree thou we are talking about 2 different animals .one will be different better of worse than the other for our needs.unfortunately these pdf's are not targeted at pi metal detectors.

[homefire]

I'm no longer sure what your trying to ask.

You asked what would be best and there is no difference. Neg or Pos Ground.

The use of P channel Fet ?

There are a number of ways to Fire the coil.

Transitors work Jim Dandy on some detectors.

A little help here.

[taliesin]

like i asked at the start

in different pi designs some coils are connected to v+ like in the hammerhead and to v- in the surfmaster.whats the consensus on which is best ?
i'm here to learn thats all.

[homefire]

They only thing I can tell you is that would depend on what parts used and how you have it set up?

I really don't think there is a best in regards to Pos or Neg.

[porkluvr]

if the coil is connected to ground and the sheild is connected to ground might the capacitance be less ?

Less than what? Where do you find any PI@ where the coil and shield are not connected to ground?

Your original question was not whether to connect the coil to ground, but whether to connect the coil to B+ or B-. (Isn't that what you really meant?)

In the vast majority of cases that answer simply rests on whether using N or P devices because that will determine whether B+ or B- is connected to ground.

@ There are some but they are not a majority.

[taliesin]

hammerhead 1