Pinpointer - Minimax-PP II

[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]

@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]

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

[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 .

[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.

[dbanner]

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

[Nandor]

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

[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]

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]

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

[Nandor]

Try components from old pcb's, those are selected ones and have very good quality! I use many from old german televisions, resistors, capacitors, transistor, almost everything you need for this project even copper wire! MCP602 can be changed with LM358 because it runs at +3 volts minimum, you only have to change the 100k resistor to 33k on the sensitivity part.
I also made Nupis pinpointer, works nice also just need to finish the final housing and design of it. I prefer the Minimax design because of the coils simplicity, just one coil and it works.

regards Marty

[MartyJ1963]

Thanks again Nandor,,,,Still awaiting parts!,,,Slow boat from China!,,Lol. I have some MCP602 chips so I'll try those first and then swap it for a LM358 and see what the difference is. I only made 1 Pinpointer so far that works great and that is the Gnom-m. It worked first time and has never given me any false signals,,,I just need to house it so I can use it in the field. Thanks again Nandor. Regards, Marty.

[andreapas79]

Hi can anyone help me? I tried this circuit but I have some problems, after bav99 (two 4148 in series) my signal is continuous, as per attached image.
coil is made with 60mm x 10mm ferrite, 425 turns d=0,315 enameled
I'm using 2n3904/6 instead 4403/1

[Nandor]

Hi
Can you post a good quality image of your pcb? It would be useful.

[andreapas79]

for now i just using a breadboard.. I'm just studing the circuit... could be this the problem?..