MPP Beach REV-E

[MartyJ1963]

Thanks 6666,,,,just need to figure out what the Reject and Gain pots do now,,,,,Still learning!,,,lol. Thanks. Marty

[Tibuck19]

what size is your 3dss coil ? your one euro is somewhat like the Canadian loonie, with my 10 inch mono loop coil(not shielded) I get a good tone 14 inches as well, A 1906 King George at round the same as well. One thing I learned here is ! when Qiaozhi suggest something, he is usually right lol

[waltr]

faulty Audio pot

Great you found this as bad pots are tough to find.

Pot labeled Reject is the Sampling delay. shorter delay tends to increase sensitivity to small and high conductive target (faster Target Tau). Longer delay rejects fast Tau targets.
Pot labeled Gain looks to set the Sampling pulse width (affect both Main & Sec samples). Wider sampling pulses tend to increase the total signal from a target.

[MartyJ1963]

Hi Guys,,,@Tibuck19,,,,,My 3DSS Coil is 10"@306uh and resistance is 1.13 ohms. This is the one I'll be using with the Rev E. I've been using a 10" 3DSS coil with the Rev D @360uh and 2.3 ohms and the detection on the Rev D with that is:- 1 Euro = 11-12" and a 5p piece at 10-11". I'm really pleased with both units. You're right about Qiaozhi, he certainly does know his stuff and I'm always reading the book he and Carl wrote,,,I still don't understand a lot but the guys on here have helped me learn a lot and I'm really grateful. @Waltr,,,,Thanks for the 'Pot' explanation,,really appreciate it,,,,So when the Reject pot is fully counter clockwise (off), is that when it's at its shortest delay? And same for the Gain, fully off , is that the 'least' width of the sampling pulses? Also, I don't know what a 'slow' or 'fast' Tau target is. It's the first time I think I've heard of the term 'Tau'. I'll sort some pics and videos out once my camera arrives and I've had a chance to learn how to use it. My enclosures and battery cases should arrive in the next 2 days so it gives me time now to shell my coil up. Thanks again guys. Marty

[waltr]

Keep reading the forum topic here. That is how I learned all this PI detector stuff.

Tau is the time a target's Eddy current take to Decay. It is this decay that induces a magnetic field the RX (sampling) detects.
Smaller and higher conductive targets decay in shorter time, Gold nuggets are such and why all the discussion about fast coils and early sampling.

You should use your scope to measure the Delay times when to turn the 'reject' pot.

Check my thread "my take on the HH2" in the Hammer Head II sub-forum. It is another fairly basic PI MD and I tried to explain all I did and learned about.

[MartyJ1963]

Thanks Waltr,,,,I'll take a look now,,,cheers, Marty

[Qiaozhi]

Both the Rev D and Rev E do now sound the same. Also,,and I'm honestly not exaggering, and I've tested it both in the Farm land and in my project room, I'm getting 14" on a 1 Euro and 12" on an English 5p piece,,,,is this good?(normal?)

Yes, this is a good result. The REV-E settings suggested in the Build Document are designed to maximize depth for coins. For less conductive targets, such as gold nuggets, this version is capable of being adjusted to cater for that situation. However, a detector intended for finding gold nuggets really needs to include a ground balance feature, but that will have to wait for a later version.

Could you tell me what the Threshold and Gain pots do and how to use them? Sorry for the foolish question but the depth tests I did were with the Gain and Threshold fully off.

The Threshold pot should be adjusted so that the audio tone is a low growl (like a geiger counter). When a target comes within the influence of the coil, the audio tone will increase. The Reject pot adjusts the main sample pulse delay, and can be used to provide a level of discimination based on conductivity. This is not the same as ferrous/non-ferrous discrimination. The gain pot adjusts the main sample (and EFE sample) pulse width. A wider pulse provides more gain, but at the expense of a small decrease in the signal-to-noise ratio.

[MartyJ1963]

Thanks Qiaozhi,,,,,You're a star,,,,I have read the build file over and over but some things still baffle me,,,,but I'm learning,,,Thanks again. Marty

[MartyJ1963]

Damping tool components?

Hi all,,,,If I make this Damping tool to set the Damping resistor of my MMP Rev D and E, can I use ordinary 1% or 5% 1/4 watt resistors with an ordinary 10k Potentiometer? Thanks in advance. Marty

[homefire]

I do and nothings gone POOOOOOF yet. 1% is always better, eaa? It's running Parallel with coil and it's not seeing that much current.

[waltr]

Since there is a pot that varies the resistance precision resistors are not needed so 5% or even 10% work just fine.
Once you adjust this to find best damping R value you remove this circuit and measure its resistance. Then pick fixed resistors to solder into the PI circuit.
You may need a combination on parallel R's to get the needed resistance.

I also use 1/4W R's and standard trimmer pot without issues.

[kt315]

CERAMIC WIRE WOUND POTENTIOMETER PPB-15E 680 Ohms 15 WATT


https://www.ebay.com/itm/CERAMIC-WIR...QAAOxygPtS6iHJ

[MartyJ1963]

@Homefire,,KT315 and Waltr,,,,Thanks a lot guys for your advice,,,really appreciate. I think I'll make the Damping tool (in the image I posted) from what I have available, 1/4 watt and some 1/2 watt resistors etc, then I'll probably order some better parts to make a dedicated Damping tool for future use,,,,I've got plenty of different value 1w-2w resistors to put in the MPP when I know what value it needs for my coil. Thanks again guys. Marty

[MartyJ1963]

@KT315,,,,I visited the link you gave but that ceramic potentiometer was a bit too pricey for me,,,$4.45 + $8.00 shipping,,,quite expensive. I may buy something like this though at a later date if I make any more P.I Units,,,It'll be good knowing I have a good quality dedicated Damping tool. What do you think to these? (See link) Would this be ok at 1k? https://www.ebay.co.uk/itm/2PCS-3590...oAAOSwc6Jagzr2 Thanks. Marty

[Andi68]

Try it in China