Surf pi detector-MOD

[kt315]

There is no need to change anything in it --- the device is great in its initial version. All other additions only make it worse and more complicated. IMHO

there are TWO mods -
1. input MOS-FET transistor instead TIP type.
2. input controlled SAT in the circuit.

that is sure seen on the schematic.

[Qiaozhi]

There is no need to change anything in it --- the device is great in its initial version. All other additions only make it worse and more complicated. IMHO

The Arduino-based version definitely outperforms the original.

The main differences between the original Surf-PI and the Arduino version are:

1. The transmitter oscillator, main, and EFE sample pulses are all generated by the Arduino Nano, thus eliminating quite a few discrete components.
2. The audio oscillator is also generated by the Nano, which has the significant advantage that the audio tone is no longer dependent on the transmit pulse rate.
3. The transmit pulse rate was increased to 1000pps.
4. The +5V supply is provided by the Nano.
5. A Boost switch was added to allow the user to switch between a TX pulse width of 50us (normal) and 100us (Boost). The Boost mode provides an inch or two of extra depth on some targets.
6. A 3R3 resistor was added between the mosfet and the coil to prevent mishaps if the coil is accidentally shorted out.

[algan]

There is no need to change anything in it --- the device is great in its initial version. All other additions only make it worse and more complicated. IMHO

I like to experiment, the most basic thing I would test is to run another power supply where plus 12 volts is gnd and use an N-channel MOSFET transistor just out of curiosity to see how it would work.

[kt315]

no, P-channel MOS-FET for Surf PI.

[Detectorist#1]

Hi algan,
No need to do modifications of the schematic (and the board) for using N-ch MOSFET switch. The same improvement for min first delay will be made with 500V P-ch transistor IXTP10P50P and with faster (and with lower noise) first OpAmp type MAX410CPA+.

[pulseinduction]

Hi! I don't know what the TX pulse width is on the Surf Pi ,I don't have an oscilloscope, I only have a multimeter, I'm a beginner in electronics, the mosfet is IRF9640, the coil inductance is 158.459uH according to the Coil32 calculator. I made a flat coil, inner diameter 309mm, outer diameter 329mm, 0.5mm wire, 15 turns, 2.5 ohm, the dumping resistance is 420 ohm. I discovered why the Irf9640 was heating up, the problem is with the R2-3.3k resistor which I changed with a 5.9k one, with the 5.9k resistor the detection distance increases but the irf9640 heats up very much, the mosfet is placed on a radiator. Another problem is the false signal, at 5.6 seconds it gives me a false signal. I made a few more changes: Q1 BC327 changed to SS8550, Q6 BC337 to BC338, C7 470nF to 1uF, C8 100nF to 220nF, U3 LM358 to JRC4558D, I reduced R35 from 33 ohm to 0.24 ohm, I use a 150 ohm speaker "SD152B" is a speaker taken from a landline phone Zapp.
I use 3 18650 batteries. I noticed that with the flat coil, the direction of the wires connecting to the PCB matters. To increase the detection distance by 3-4 cm, the wire on the outside of the coil is connected to the GND pin, and the wire on the inside to the L1 pin.
The detection distance is good in the air, I have not tested it in the ground.With LM358N and R2 -3.3k it detects: 1euro -34 cm, 2euro-38cm, 4 cm gold coin at 42cm, beer cap-40 cm, beer can- 80cm. With R2 3.3k changed to 5.9k the distance increases but the mosfet heats up: 1euro-43cm, 2euro-45cm, gold coin-52cm, beer cap-48cm, beer can- 96cm. With JRC4558D and R2 changed to 5.9k the distance increases even more, but the MOSFET is hot: 1 euro - 50cm, 2 euros - 53cm, gold coin - 60cm, beer cap - 54cm, beer can - 110cm. What should I do to get rid of the false signal and stop the irf9640 from heating up, but keep R2 at 5.9k to have a longer detection distance.

[pulseinduction]

I forgot to mention that I built the other version, not the long version

[Ruben2000]

Good morning, pulse induction!
You've encouraged me. I was about to continue assembling my SurfMaster PI PCB, but I had an accident, which prevented me from doing so. I'll start by placing the power supply components and will keep you posted in this thread.
I recommend being careful when changing any components, as this can cause the detector to work differently, especially if you can't see the signal.
I built the SurfMaster PI before, but I wasn't successful. I hope to do it correctly this time.
As I assemble each block, I'll note down details.

[scs-bg]

Remember that too much depth of detection in air tests leads to problems in real use. You get a strong signal from the ground and unstable operation. It's all a matter of reasonable compromises.

[Detectorist#1]

Hi scs-bg,
I'm absolutely agree with you - shorter first delay gives good results in air tests but is not useful in real work on the ground!

[Ruben2000]

Hello friends!
Here's the PCB schematic that Algán shared.
This schematic is drawn exactly as it appears on the printed circuit board.

[Ruben2000]

I will start by soldering the Power Supply part

[GeoMax]

Hello Ruben2000,

Although this circuit diagram resembles a Surfmaster PI, it doesn't correspond to the real SurfPI circuit. The original SurfPI doesn't have an IRF9640 MOSFET and also has an internal and external delay potentiometer. The circuit diagram you posted only shows an integrated potentiometer and a resistor in series. In the original SurfPI (circuit diagram and board), the coil is driven by a TIP32C transistor. The SurfPI Pro, which is similar to the SurfPI, has an IRF9640 MOSFET. The SurfPI Pro also has a GAIN potentiometer. These are the obvious differences I've noticed so far, and there may be more.

[Ruben2000]

Hello Geomax!
Thank you very much for the clarification.
I just want to learn more about how PI detectors work. Although I wasn't successful the last time assembling this detector, I want to test which components work best for me.
However, I see that there are different schematics for the Surmaster PI, and that confuses many people, each with their own mods.
If you have the schematic for the Surf PI Pro, I would appreciate it if you could share it with us so we can also get an idea of what I'm doing.

[GeoMax]

Hi Ruben2000

you can find the schematic here in the forum at this link, post #1 Surf PI Pro - Geotech Forums