Surf Pi Pro Build

[cddz]

How important is setting the dampening resistor? With the 390r that comes with the kit I think I have a 15 uSec delay. I used a pot as recommended, I only noticed a 1 usec difference. Not sure where to actually set it. at 950 ohms I get the ringing, at 920 it is gone. If I adjust until there is no improvement in delay I am at 490 ohms. Which value should I use? This is what it looks like with the 390 ohm R6 installed. I thought I grabbed a screenshot of the other values...

[FatBob]

Well you want the highest resistance possible without ringing. So 900, 910 or 920 would be best for that coil. Lower values will overdamp and you will not see small targets.

Small gold decays very fast and you don't want to miss it!

[kt315]

Which value should I use?

there is good book for all useful Q and A. Inside The Metal Detector its name. good for any reading believe me now.
so I answered on your Q Which book should I use?

[cddz]

I have looked at that book, going to order it. Why would a coil require such a high R? Most of the time I have read that coils want 600-700 ohms.
23 turn 22 awg enamel wire 228mm diam, measured L is 310uH

[kt315]

http://www.geotech1.com/forums/showt...i-Coil-ringing
http://www.geotech1.com/forums/showt...ore-on-damping

try use SEARCH engine of forum. coil ringing or critical damping. with mine english i am not able to say you more.

[cddz]

I have used the search function, that is how I came to build the Surf Pi Pro. I was just asking why it would need to be so high is all. I don't think you are understanding my question.

[kt315]

I am understanding all you write. a coil has L C and R data ie has a self resonanse. is it clear for you?

[cddz]

Yes it is clear. The question I was asking is why it would need to be so high. I normally see reference to a lower value. I was asking the experienced coil builders is all. It has been 25 years since I have studied Electronics(analog). I am a bit rusty. What does a high R value for dampener indicate about the coil? Thank you for your help thus far.

[kt315]

can you show pics of your coil? what type of cable you used? how its shielded?

[cddz]

It is 23 turns of 22 AWG enamel magnet wire, 9 inch diameter. 310 uH, .8 ohm. I have not shielded it yet. Thank you

[kt315]

ok. no cable. your o-scope pic done in a room.
can you do the o-scope pics if the coil being:
- at hard soil australian ground
- in salt water
- at american black sand beaches
?

kind regards

[Qiaozhi]

How important is setting the dampening resistor? With the 390r that comes with the kit I think I have a 15 uSec delay. I used a pot as recommended, I only noticed a 1 usec difference. Not sure where to actually set it. at 950 ohms I get the ringing, at 920 it is gone. If I adjust until there is no improvement in delay I am at 490 ohms. Which value should I use? This is what it looks like with the 390 ohm R6 installed. I thought I grabbed a screenshot of the other values...

The sample delay looks to be around 16us from your scope shot, and there is a slight amount of ringing. In this case, the damping resistor value of 490R seems to be correct.

You can get a more accurate measurement of the sample delay by probing the TX oscillator output on channel 1, and the preamp output on channel 2. Set the scope to trigger on channel 1.

[cddz]

I wish this Surf Pi Pro had test points on it . Is that pin 13 and pin 5 of the CD4066?

[daverave]

i also have surf pi and my coil damping is around 450 ohm with no ringing and my coil is 400 uH and i can sample at around 10 uS and i can detect low conductive items very good and a thin chain with clasp at around 4 inches.

[6666]

I wish this Surf Pi Pro had test points on it . Is that pin 13 and pin 5 of the CD4066?

The trick is to leave some of the component legs long, makes good test points.
IE: with voltage regs keep legs long and raise the component above the board so you can probe the legs.