Surf Pi modifications (clarification needed)

[ulix]

Hello,

I was thinking of building a Surf Pi detector.
I have some Questions which I could not be clearly answered in all the threads about the surf:

a) how can the Surf Pi be modified to detecto gold? I read about modifications, but not where to make them
b) how to make the Surf Pi compatible for low impedance audio devices? What components would be needed?

Thank you very much

[ionut_mtb]

Hello,

I was thinking of building a Surf Pi detector.
I have some Questions which I could not be clearly answered in all the threads about the surf:

a) how can the Surf Pi be modified to detecto gold? I read about modifications, but not where to make them
b) how to make the Surf Pi compatible for low impedance audio devices? What components would be needed?

Thank you very much

Hello,

First you have to build it, understand how is working, set it right... Is long road ahead if you have no knowledge about metal detectors and of course electronics in general. Surf Pi can be modified to be more sensitive to gold, but for that you need to adjust it starting from the original build (oscilloscope is needed). It will detect all type of metals, not only gold, it does not have discrimination. As for low impedance headphones you can use a stepdown transformer, aprox 500/8-16ohm.
You can also use search engine, you will find a lot of answers. We all started somewhere.

Enjoy!

[Qiaozhi]

Hello,

I was thinking of building a Surf Pi detector.
I have some Questions which I could not be clearly answered in all the threads about the surf:

a) how can the Surf Pi be modified to detecto gold? I read about modifications, but not where to make them
b) how to make the Surf Pi compatible for low impedance audio devices? What components would be needed?

Thank you very much

If you mean "to detect only gold", then you're wasting your time.

However, if you mean "to detect small high conductivity items such as gold nuggets or fine jewellry", then you should look at the MiniPulse Plus, as this detector has a dual-stage preamp specifically designed to handle short sample delays.

[ulix]

Hi ionut_mtb and Qiaozhi,

thanks a lot about your feedback. About electronics and measurment stuff, I should have everything on board

I meant, make it more sensitive to high conductivity items (I know, PI's will allways detect iron...)

One Reason was not to got for the Minipuls Plus, it would have a bigger pcb and has no mono coil?. I want to squeeze it into a tiny case. But it would accept low impedance headphones...?

@ionut_mtb: Is there no other alternative to a big+heavy transformer?

Thanks

[kt315]

are you diver? why you want to build specific detector for diving?

[ulix]

Hi,

@kt315: no I'm not a diver. I want to build a detector mainly for beach detecting. With a depth about 8 inch (20cm).

I really want to come back to the speaker low/high impedance question... I don't really understand why a low impedance will alter the functionality of the detector...
Q1 is for allowing to "activate" the speaker when metal is detected. Would it not be possible to change the voltage the P2 (headphones) are sourced, or to alter the resistor values? (Talking about this schematic)
Adding D1, C5 would it alter the functionality of the Surf Pi Pro? Is only for protection/stabilization?

[kt315]

again same question. underwater headset is PIEZOCERAMIC one, NOT you maybe guess thats ordinary type
you wear now with pc. the piezo is some kinda A CAPACITOR, ceramic plate with metal layers on both sides, and HAS NOT 'Ohm' conductivity AT ALL.

is it OK for you?

[kt315]

[kt315]

[ulix]

Thank you kt315. But I'm more interested why a low impedence speaker would not work in the surf pi circuit.
cheers

[Qiaozhi]

I meant, make it more sensitive to high conductivity items.

You would need to change the preamp from single stage to dual-stage (like the MPP).

One Reason was not to got for the Minipuls Plus, it would have a bigger pcb and has no mono coil?. I want to squeeze it into a tiny case. But it would accept low impedance headphones...?

The MPP can use both mono and balanced coils.

Is there no other alternative to a big+heavy transformer?

I fairly certain that I've run the MPP using an 8 ohm speaker, although the one I have on the bench is using a 64 ohm. Unless someone else can confirm what they're using with the MPP, I could try an 8 ohm to see the difference.

[ulix]

Why would change the resistance of the speaker change the behavior of the detector? On both the Surf Pi and Minipuls Plus...

The impedance of the speaker would only change the volume, wouldn't it? Maybe when the resistance of the headphone is so small, it would destroy the audio switching transistor (or am i totaly wrong?)

[kt315]

where you see resistance of speaker if there is not resistance of speaker? HEY! STAND UP BUDDY!
either i am idiot or... why people with zero basic in electronics thinking here are the teachers of electronics?
if i am teacher so why you do not want to hear me?

this is ORIGINAL White's SURF PI schematic particle attached.

[dbanner]

If you intend to use it for beach hunting then headphones are probably the best choice. With headphones you can hear faint signals better. My advice is to build the standard surf pi pro, get it up and running, then you can modify and tinker for better audio and performance.

[ulix]

@kt315: I don't know what you want... YES i know, the symbol you marked is a piezo!

A piezo speaker has high impedance (high resistance), some headphones have low resistance. WHAT and WHY will low impedance headphones alter the function of the detector?