Pinpointer - Minimax-PP II

[MartyJ1963]

Thanks Nandor. Still waiting on parts to arrive then I can start to build, Regards, Marty.

[Nandor]

Yes, because it has reverse pins. I always check with Multimeter In the past had problems with reverse pins, so I learned not to forget to use the multimeter first, for used parts even more important.

[MartyJ1963]

Hiya Nandor,,,,Which is the correct Orientation of the BC547?,,,On your PCB it is the opposite way to the Sprint layout,,,Thanks, Regards, Marty

[Nandor]

I was thinking of some kind of shielding for th pcb also, its sensitive to hand capacitance.

[dbanner]

Use a graphite shielded pipe for the coil. Prevents falsing.

[MartyJ1963]

Thanks Nandor,,,,I will follow your advice and have a go building this pinpointer,,,,I'll let you kno how it turns out. It may be next week because I bought some good quality fr4 copper and the fibreglass is really thick so I had a hard time cutting it the usual way with a stanley knife,,I'm just finishing making up a small Mini Table saw for cutting pcb's so I'll begin once I've completed the saw. Thanks again,,,Marty.

[Nandor]

By the way, I used shorter 0.25mm wires sodered together for one of my coils. Salavaged from old pcb's, the other is from CRT Tv tube coil, it has almost 20m of wire and it's also 0.25mm. The only thing is not to put too many turns because it will drop the frequency. Try to get around 4-5cm for a Euro coin, if you search the yutub you will see that many factory made pinpointers have less range than MiniMax 2. Also we need a pinpointer not a long range locator .

[Nandor]

I think shape is not so important here, but inductance is more. This detector is a voltage drop sensor, as metalic object approach the coil its quality factor drops so the oscillators voltage will also drop. Now there is is MCP602 which is used as a comparator and it turns on the Piezzo because the voltages on its inputs are unequal. The trimmer pot is for setting the reference voltage for the comparing. It work with almost any coil, use what you can and what you have the oscillator cant see what you hook up to it, it will be happy to work!
Best regards Marty

[MartyJ1963]

@Nandor,,,Thank you kindly for the coil data and advice on materials and frequencies, it will be a great help, you are a gentleman! I have a piece of radio ferrite that is about 8-10mm wide x 40 - 50mm long but is only about 5 - 6mm thick. Will this be ok? and will it matter if I wind 400 turns or better at 500 turns? Thanks again for the help, much appreciated, Marty

[Nandor]

Hi Marty
I have tried different ferrite rods, even from PC power supply. Those little rods are good for space saving but if you want better sensitivity use radio ferrite. It has 8-10mm diameter and at least 5cm long so you can put on 400-500 turns. The frequency will change a lot. I have made coils with 7.8kHz and 14.5kHz, but if you want you can change the oscillator capacitors also, I had 470pf and 10nf capacitors at hand. Its very tolerant on coils.

[MartyJ1963]

Thanks for the files Nandor,,,What are the coil specs for this design please? Thanks and regards, Marty

[Nandor]

Interesting observation Koala!
Well it's getting nervous if I touch it surely needs some kind of shielding for parasitic capacitance. The most difficult part for me is to find the proper housing for it.
The legend says that this circuit works also with LM358, just a little components change is needed.

[Koala]

Before you epoxy it up. I would check outside

I have built several pinpointers. None have worked as well as a commercial.

They are fine 100% on the workbench and not too bad at finding cables or pipes in the wall.

But useless when searching a dug hole. First it nearly always detects the hole. So switch it on close to where I need to pinpoint to recalibrate.

Change its direction to check the other side of the hole and it starts to go wild. Also detects the bottom of the hole if its damper.

Guess its my coils. Do they need to be shielded ??

Its not the ground as a cheap GP Pinpointer is fine

[Nandor]

You know what? I will call this pinpointer The Parrot!
I cant wait to hear it finding some coins.

[Eddy71]

That's an interesting sound. I thought the parrot was screaming.