FM2 on steroids

[dom44]

Just built the prototype for the FM2 with improvements I changed the oscillator stage and added an amplifier to it.
it now will pick up small specks of gold and coins at a larger distance software is the same its def an improvement in range and sensitivity I am still finishing of details will post a vid soon.

[MartyJ1963]

Hiya Dom44,,,Nice PCB Layout,,,I'll try to make it,,really like this little pinpointer,,,Could you please tell me what the Coil data is please?,,The schematic mentions 200 Turns and 40 Turns but not not UH/MH. Thanks. Marty

[dom44]

I am still playing with it but works well can pick up a knife blade at about 8" and very small nugget at 1/2" the value of R19 is important use a pot and find the right value then replace with resistor.

[MartyJ1963]

Hiya Dom44,,,I've made a few different pinpointers over the last 2 months,,but can't seem to get any to work decently,,,but I like this little pinpointer a lot,,,I made one (FM2 ) and it detected pretty good but after 10 minutes there was no sound any more only the LED's indicated metal. I'd like to try your modified FM2,,,could you tell me the Coil data please iin uh/mh/frequency. Really appreciate it. Thanks. Marty

[dom44]

the problem with the FM2 is it is using frequency shift to detect so the frequency has to be in the range eddy designed it for or wont work at all and you need to hit the re tune button often. the coil i am using is based on the falcon metal detector its just a 50mm long ferrite rod about 10mm diameter with with 2 pcb
washers glued to one end then wind on 40T tap then 200T i then place copper tape as a shield leaving a gap in it solder the shield to the earth end of coil.

this image is for another detector space the washers further apart to add more turns
and when mounting the coil drill a hole in the housing end you are using to let the ferrite rod go through the plastic so it is flush with the end so you get max sensitivity as even the plastic end piece can attenuate the signal.




PCB

[MartyJ1963]

Hi again DOM44,,,,,thanks for the data,,,you explain things really well and make it easy to understand. I will try to build this and let you know how I do.Could you let me know the values in the photo please? I have all the components and copper clad to make it apart from the 2 Transistors. Thanks again. Marty

[dom44]

the unmarked resistor is R19 place a 1M pot to test for right value use a scope if you have one varies the signal amplitude and shape, i used a BC549c because it is low noise high gain NPN replace with something similar. the MPS42 is high voltage transistor because i am going to use a peizo speaker with 22MH choke across it to save power and the choke causes high voltage spikes to give more volume from the peizo.

[waltr]

Looks interesting.
Can you post a link to the PIC code please.

[MartyJ1963]

Thanks DOM44,,,really nice of you to help me,,,I have a Hantek DSO 5102P Oscope,,'m stll learning how to use as I haven't had it that long,,Could you tell me where I would place the probes please and what I should look for? I really appreciate the help in learning. Thanks. Marty

[dom44]

http://s000.tinyupload.com/?file_id=94553900157730276270

remove the chip and test at pin 6 of the chip output of the amp. you can see the wave shape and effect of different metals on amplitude and frequency.
the trick is at the best settings you will get maximum wave change from the best distance possible with stability.


Small error found on circuit diagram R17 is 120k not 1k it is shown correct on PCB
and C9 is 1nf not 10nf

[MartyJ1963]

Thanks Dom44,,,very kind of you to help me along. I have everything to build apart from MPS42 and BC549C so I will have to order some or look in my componets to see if there are any alternatives,,,can't wait to build this little detector,,thanks again. Marty

[dom44]

if you want Marty can replace the MPSA42 with MPSA13 or BC517 Darlington and replace 47R to 100R to drive an 8ohm speaker

[MartyJ1963]

Thanks DOM44,,,,,you really are a gentleman!,,,,I have a separate Hard drive (1TB) that I use just for my Electronic books, Electronics software, PCB Layouts etc,,,,If there's anything you're looking for regarding Detectors and Electronics info, don't hesitate to ask,,I'm willing to help anyone I can just like your kind enough to help me. Thanks again.

[dom44]

thanks Marty i am just an experimenter like others on here I just tend to think outside the box a bit, plenty on here that know more than me just surprise we don't get more improvements from them, just more of the same with the knowledge base here we should come up with a detector that would put anything commercial to shame.
Every older detector i look at have shortcomings that could be improved but instead we just get copies shortfalls and all, no one improves the receiver front end or transmitter to get better performance how many mediocre detectors can one build.

[MartyJ1963]

Thanks DOM44,,,Yes, it's a great little forum Geotech,,I wish I had found this Detector hobby years ago,,,all my life's been spent in the ,Carpentry and Martial arts business,,,I've always been able to fix guitars and stompboxes as far back as I remember but building Detectors opened up a lot more Electronics interest for me. I used to go gold prospecting and sapphire hunting with my Dad and my Uncle when I lived in Australia but that was in 1977 and I never got to try using a detector until 2 years ago. Absolutely love it now,,lol. I'll sort through my components tomorrow and see if I have everything so I can start my build,,,I have some mpsa13's,,dont know about what I have yet to substitute the bc549c. Thanks again for the help Dom,,,regards, Marty