New Homebrew Metal Detector

[Geo]

Hi Ivconic. If you still work with D.P then i can send you the manual. I found it.
Btw I believe that for big objects 100hz is better than 400 hz
Regards

[zisme]

I made a several coils yesterday and today. Experimenting and gain no better
results yet. Still best result is coin detection from 20-23cm with coils 24 diamm.
I do not see some differences, no matter number of windings, from 20 to 40... IRF 740 is still cool.No problems with apparatus at all, only could'nt
match better coil so far....
The same problem i had with Delta Pulse at the time.But solved later with some modifications. I made spiral coil, started as told here, but windings finished much before 9.5 in...!? WIre gauge is proper...
Although i noticed a slice better performances of spiral than conventional coil. But very slice.....1cm more on the coin...
Still experimenting...
See you later..

One thing I noticed is that you said you were getting about 225 Hz. out with the substitute crystal you installed. When I did the math, I came up with 111.7858887 Hz. which is about half of what you are getting which means the your oscillator appears to be operating at twice what it should be. I don't know if this makes any difference or not in the range you are getting, but in troubleshooting, you should start with the original frequency of about 100 Hz just to rule that aspect out. If the oscillator is running at twice it's frequency, you might try playing with the value of C3 or just try to get hold of the correct crystal. These are common color-burst crystals that you can get for as little as 10 cents each.

I checked the wire gauge and coil again and it's correct. The spiral winding is close-wound with no gaps. If you are not getting the diameter, go to a larger gauge wire. In fact, this should increase the Q and maybe improve your results.

I assume you have experimented with all of the timing adjustments. These should be fine tuned to get the best results from a given coil.

Also, another difference between your detector and mine is the current draw. My detector draws much more current than yours which means it's putting more current into the coil. Of course, mine is running at 109 Hz. too.
You said you left out the voltage regulator, what is your input voltage? If you drop below 12 volts, the range starts to drop off quickly.

Again, thanks for the feedback and good luck.

Keep us posted,

Mike

[ivconic]

Same results ...


I made a several coils yesterday and today. Experimenting and gain no better
results yet. Still best result is coin detection from 20-23cm with coils 24 diamm.
I do not see some differences, no matter number of windings, from 20 to 40... IRF 740 is still cool.No problems with apparatus at all, only could'nt
match better coil so far....
The same problem i had with Delta Pulse at the time.But solved later with some modifications. I made spiral coil, started as told here, but windings finished much before 9.5 in...!? WIre gauge is proper...
Although i noticed a slice better performances of spiral than conventional coil. But very slice.....1cm more on the coin...
Still experimenting...
See you later..

[ivconic]

Thanks..


Thank You very much. I'll visit your site again and update news...
Right now i am experimenting with coils... I 'll report here any news on that subject..
regards!

[zisme]

I forgot to mention very important thing !!!
Instead of 3.5xxx quartz i put 3.663 MHz quartz.Also instead 27p i put 30p capacitor...
The freq. is 225Hz. I think it is even better cose could be a bit more sensitive on
small items - who knows? Those jumpers can be arranged some other way to obtain
different freq. i suppose.... I do not have right now any manufacturer aplication here,
so if you want, may post here inner composition of i.c. with all jumper presets available.
I was thinking to add some switches instead jumpers, so i can choose working freq. by it,
later, without opening box or rearranging jumpers.What do you think? It brings to me a
bunch of new ideas right now...!
Anyway, the fact is that this device is much simplier than Delta Pulse, which i prefered
so far, so if gain with it even close results like with D.P. i will "switch" on it in the
future....
Last step is to "establish" the proper coil for it.
I am waiting for you hints, and later i am gonna start making some coils here...ha,ha,ha!
regards


P.S.

Also i omited low drop reg. and connect it straight to 12v accu, 1.3A...
No big use from low drop if you use powerfull accu, only have to add 4700mF
and all is "singing" nice...

Nice Job! I am amazed you are operating it without any regulator! You guys are already improving it!

I really enjoy hearing from folks like you that are having as much fun with this project as I have had.

Sorry for leaving out the inside diameter of the coil. The I.D. is 5.75 inches. I made a coil winding jig with a center disk that's 5.75 inches in diameter and wound it outward untill I had the number of turns I needed. It just happened to come out at 9.5 inches O.D. so that's what size housing I then built for it. I have added the coil I.D. to the webpage.

As for the frequency selection jumpers, I have added a chart on my website that shows all the possible jumper configurations and the resulting frequencies out with a 3.579545 mHz. crystal.

Glad you like the circuit,

Mike

[ivconic]

More...


I forgot to mention very important thing !!!
Instead of 3.5xxx quartz i put 3.663 MHz quartz.Also instead 27p i put 30p capacitor...
The freq. is 225Hz. I think it is even better cose could be a bit more sensitive on
small items - who knows? Those jumpers can be arranged some other way to obtain
different freq. i suppose.... I do not have right now any manufacturer aplication here,
so if you want, may post here inner composition of i.c. with all jumper presets available.
I was thinking to add some switches instead jumpers, so i can choose working freq. by it,
later, without opening box or rearranging jumpers.What do you think? It brings to me a
bunch of new ideas right now...!
Anyway, the fact is that this device is much simplier than Delta Pulse, which i prefered
so far, so if gain with it even close results like with D.P. i will "switch" on it in the
future....
Last step is to "establish" the proper coil for it.
I am waiting for you hints, and later i am gonna start making some coils here...ha,ha,ha!
regards


P.S.

Also i omited low drop reg. and connect it straight to 12v accu, 1.3A...
No big use from low drop if you use powerfull accu, only have to add 4700mF
and all is "singing" nice...

[ivconic]

It is working !!!


Hi again Zisme !
I've just finished this PI. It works fine from the very start.
I just did'nt make coil you posted here yet. I tried detector with
some scrap coils, already have here. Although it is not mach, it works
almost fine with it!!!
For example: 1.5cm brass coin it can detect on 20cm distance ,
with 21cm diameter coil,with 31 windings and 0.7mm wire gauge.
I am not thrill with this result but of course the presented coil is not
suitable for it,not proper. So, i decided to make your spiral coil,and
only one thing is buging me. You mentioned 9.5 in diam. But,looking
at your coil i keep wandering what of the two axis here(on my picture)
should be 9.5 in.Inner or outer? If you started with first winding from
inner, how did you knew in advance,that it's gonna end just on 9.5 in?
If not, than otherwise you must started from outer point on 9.5in circle
wound from outer to inner axis? This i ask cose want to make exact coil
as yours, due to very good results you posted here.Many thanks in advance!
By the way, IRF is calm and cool, no noise, and power consumption is 24mA
without detection(no sound) and 98mA with full detection(loud sound)...
All presets are working just fine, also 2 potentiometers also...
What to say!? Nice project and working at once! No problems at all!
Congratulations!
best regards!
P.S.
waiting for hints about coil...

[ivconic]

Regards...

Regards !
When finishing i'll post some reports here...

[zisme]

here is a handmade pcb....

Wow! I can't believe you made this by hand! Great job!

Don't forget to install the three jumpers first. lay them flat.

If you need any help in getting parts, or adjusting it, let me know.

Again, thanks,

Mike

[zisme]

Hi Zisme ,
this looks interesting to experiment with!
My handmade pcb is ready, now i am waiting components from provider....
Can you tell more about used coil here?

"If your MOSFET is getting too warm to touch at the TX frequency you choose,
use thinner wire in your coil or add a series resistor of about 2 to 4 ohms and
most importantly, add a heat sink!
....If the MOSFET is getting warm that means that you have exceeded the voltage
rating of that particular MOSFET......(bbsailor)"

A higher peak pulse voltage makes fet hot. (IRF 640-200v, IRF 740-400v....)etc.


regards

I just wanted to say that I am not having any overheating problems with the timing values I am using. I have added the following to the website to clear up the confusion:

(Added on 6-10-06: I have been receiving e-mails with solutions for reducing the heat in Q1. I wanted to clarify this. Q1 does not get hot with the timing settings I am using. I only included heat sinks on Q1 and the voltage regulator to allow room for experimenting without worrying about overheating these devices. The pot values indicated can allow enough room for adjustments to reach a point where Q1 and VR1 will warm up, but when properly adjusted for best results, you will not have any overheating problems. In fact, the circuit board I used in the completed detector does not have them. Mike)


I couldn't tell you much more about the coil except I did make a coil winding machine in order to wind it. It still didn't turn out much better than just winding it by hand.

Great to hear that another person is building it. Please let me know the results.

Thanks,

Mike

[ivconic]

pcb

here is a handmade pcb....

[ivconic]

Hi

Hi Zisme ,
this looks interesting to experiment with!
My handmade pcb is ready, now i am waiting components from provider....
Can you tell more about used coil here?

"If your MOSFET is getting too warm to touch at the TX frequency you choose,
use thinner wire in your coil or add a series resistor of about 2 to 4 ohms and
most importantly, add a heat sink!
....If the MOSFET is getting warm that means that you have exceeded the voltage
rating of that particular MOSFET......(bbsailor)"

A higher peak pulse voltage makes fet hot. (IRF 640-200v, IRF 740-400v....)etc.


regards

[Esteban]

Search for keywords bbsailor and read all instructive hints about PI coils.

[zisme]

25x25cm copper plate at 90cm.Is this enough or can i make it better?
Also the current is 20 to 40 mA without vco, when i have sound the total current is about 100 to 120 mA.Is anything wrong?

That sounds like a good distance if you are using the 9 1/2 inch coil. I would have to find a 25 cm copper plate to know for sure. I used the following test:

U.S. penny: 12 to 15 inches

U.S. nickel: 9.5 to 10 inches

I would think you might get even better results with a better coil than what I am using. Others have suggested that using Teflon insulated wire or Litz wire will give better results. Also, I glued my coil to a piece of composite fiber board and mounted it inside a case made of the same stuff, which lowers the Q somewhat. The best coil would probably be one that has no surrounding case, but the windings are just held together with epoxy or some other glue. The addition of a shield was suggested, but it seemed to reduce the range a little without improving anything. I am in the process of making a new light-weight coil. I will post the results ASAP.

You can also experiment with the timing to try and improve your results. The charts I supply, are for reference only and are optmized for my coil. Different coils will mean different timing setups, so even if you have a coil made in the same dimensions as mine, some deviation in adjustments will probably improve it.

The current drain on yours is actually a little better than mine. If you are using a speaker for the transducer, make sure that R26 is not installed. Also, raising the value of R25 will lower the current with the audio on. This lowers the volume too, but I think it's too loud anyway. For best current drain, use a piezo transducer.

As I say, this project is a basis for experimentation and improvement, so go at it and let me know your results.

Thanks for the questions and thanks for building it,

Mike

[Geo]

25x25cm copper plate at 90cm.Is this enough or can i make it better?
Also the current is 20 to 40 mA without vco, when i have sound the total current is about 100 to 120 mA.Is anything wrong?

The detection distance is very good for a coil 8 to 11 in but no good for biger coil. Now about current if i will see the diagram of detector i can tell you but i believe that 100ma is a normal current for a PI detector.