Pinpointer - Minimax-PP II

[ta2cjj]

MMBT4401 : 2N4401

[Nandor]

[dbanner]

Under third wave lockdown, so I decided to make minimax pinpointer.
I didn't have an active buzzer, so I made CD4060 add on board posted on previous page to generate the sound. Someone described this version sounds like a parrot, and well, it does! Just awful.
I needed a beep beep circuit and I found just the one. It works extremely good.
Based on 556 dual timer. Now minimax is sounding like the real deal. All I needed to do was to change C1 to 390nF. If like me, you don't have an active buzzer in your junk box, but you have couple of 555 timers, then build this circuit, it is the best beeper for minimax.

[andreapas79]

effectively the value is different, pnp 134, npn 198... could be it the problem?..... if yes now i understand why ne555 to generate function to pilot coil..

[Nandor]

Well transistor pinout can be a problem, try the pcb with matched pair of transistors. Measure their hFe with a multimeter and try to choose 2 indentical one. Like PNP with 190hFe and NPN also with 190 hFe, or any other other just it has to be close to each other.

[andreapas79]

Thanks for your help. I have not yet build pcb because I'm experimenting, but if this gives all these errors i build a pcb. It's really strange from 150v to 1,4V.... could the 2n3904/6 replace BC807 / BC817 without problem ? can't that be the mistake, right?

[Nandor]

Well it should be a clean sine wave, I think it's a transistor that works bad on your board. Try to make the pcb it will work, it's an easy pcb to make, I drawed it with a marker pen and ruler.
I tried many coils, it works with allmost anykind of coils. If you use thick wire it will consume more power, 0.31mm is good and also 8mH it's only frequency thats changes. The best I could get was around 5cm for a big coin, but I don't think that it needs more detection range because we need pinpointing not a locator.

[andreapas79]

yes thanks a lot... i dont understand why it give me only 1,45V...how is your coil? I've a ferrite rod 10mm x 55mm with 450turn 0,31 enameled copper wire, 7,95 mH 6.8ohm...i dont understand why the voltage is so low.
I've attached a photo of a quick measurement

[Nandor]

Hi
I just measured mine again. so the Oscillator has 135volts peak to peak at 15,6kHz. After the diodes it drops to 64volts DC negative! When detection occures it drops to DC -54volts.

Hope this helps

[andreapas79]

I made the same with stripboard.. the signal looks like better but, after two 4148 the signal is near zero, before 4148 i've 1,4V sine wave...it's normal this value?
I used 2n23906 and 2n3904, 490pf and 10nf

[andreapas79]

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

[Nandor]

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

[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

[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.

[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