Detector Build Stumbling Blocks

[waltr]

Another thing is when building your first metal detector even when you know electronics is learning how it should work and how each of the circuits should work.
It took me 4-6 months to get my first PI detector to work, 3/4's of time was correctly building the coil. Second one took a week.
Same when I then build a VLF detector (TGSL). The detect circuit took a few days but to get the coil working correctly was another couple of months.
Without a O'scope getting either of them working properly would have been impossible.

[Infamy]

I don't think I'm making assumptions. You actually wrote: "[I] don't have an oscilloscope or can't use one."
Without an oscilloscope your chances of success will be minimal.

Crossbow is only difficult to build for those with limited electronics knowledge, as there is no build document for that detector since it was never intended as a Geotech project.

I wrote "I keep reading the same stuff in some of the build videos, I'd like to build that detector but don't have an oscilloscope or can't use one." The points I was making
1) Big rise in cost of components.
2) Lack of specialist supplier.
3) Conducive conditions for someone to fill the DIY supplier void and bring costs down.
4) Conducive, bring people into the DIY world, welcoming environment, growing market not declining.
5) Barriers to entry, having and being able to use test equipement.

PS I have a couple of Oscilloscopes one dead too difficult to take apart without causing damage, and a PM3055 with a confusing layout. I use it to fix audio equipement CD players mainly, amps and the odd turntable. I bought 50 plus pieces, to understand the market and maybe later supply specialist components.

Living in France, while Brexit is a bad news for small business in the UK it makes opportunities else where. But at the moment I'm here because I need to build a specialist piece of equipment which is not on the open market in one affordable package. I wrote a couple pieces back in around 2008-2009 the Autonomous treasure hunter and using GPS RTKlib to produce surveys which could be accurate overlayed, Mag. results used to cancel out iron in PI results. So I'm finishing that project and think the Crossbow Classic design is something to look at.

PPS I appreciate you making the Crossbow Classic avaliable to build.

[Infamy]

Hi Infamy,

to answer your question of which capacitor to buy... Actually it depends very much were the capacitor is connected within the circuit and which voltage is applied across and/or possible to be expected.
Therefore, there are many types of capacitors for various needs in the market. The best would be following the recommendation by the circuit designer, if you do not have good electronic background knowledge.
Alternatively, you can upload the circuit diagram and let us know to which capacitor you are referring within the circuit. That might help to find the answer easier.

GeoMax

No voltage values given for the Crossbow Classic capacitors. My approach without the info would be to start with MPP Beach values but change 1000 uf cap to 25 volts the rest are all 10 volts.

[Infamy]

Infamy, metal detectors are not difficult to build as long as you don't make a mistake. If you do make a mistake and don't have an oscope, then you're dead in the water. In any case, if you want to plow ahead I suggest you just start asking specific questions. On the caps GeoMax is right, "it depends." Ferinstance, the cap on the TX driver needs to be low ESR so a polymer type is best, and multiple parallel caps even better.

If you use audio grade caps over all is this likely to result in a more stable and sensitive detector than lower grade caps?

[Infamy]

Another thing is when building your first metal detector even when you know electronics is learning how it should work and how each of the circuits should work.
It took me 4-6 months to get my first PI detector to work, 3/4's of time was correctly building the coil. Second one took a week.
Same when I then build a VLF detector (TGSL). The detect circuit took a few days but to get the coil working correctly was another couple of months.
Without a O'scope getting either of them working properly would have been impossible.

What is it exactly about building coils that is difficult?

[waltr]

What is it exactly about building coils that is difficult?

For PI detectors it is getting the coil fast enough to detect small and low conductive targets. This includes the cable from circuit to coil.

For VLF detectors it is getting the Exact inductance to resonant at the correct frequency. Then the Nulling of the Receiver coil is very, very touchy.

For both is creating an effective shield that doesn't decrease sensitivity.

Another issue many have is all the EMI in and around one's workshop that kills sensitivity and can create lots of false issues sending you on a wild goose chase.

Form here has lots and lots of posts about issues on building and tuning coil.

[Carl-NC]

No voltage values given for the Crossbow Classic capacitors. My approach without the info would be to start with MPP Beach values but change 1000 uf cap to 25 volts the rest are all 10 volts.

I look at the voltages that get applied to the caps, double that, and use that as guide for selecting the cap voltage rating. Ferinstance, if the cap is on a 5V supply I would use a 10V cap minimum. But 25V or 50V will work just fine.

If you use audio grade caps over all is this likely to result in a more stable and sensitive detector than lower grade caps?

Probably not. In many cases it will make no difference. In fact, sometimes the cap might not even be necessary.

I wrote "I keep reading the same stuff in some of the build videos, I'd like to build that detector but don't have an oscilloscope or can't use one." The points I was making
1) Big rise in cost of components.
2) Lack of specialist supplier.
3) Conducive conditions for someone to fill the DIY supplier void and bring costs down.
4) Conducive, bring people into the DIY world, welcoming environment, growing market not declining.
5) Barriers to entry, having and being able to use test equipement.

The rise in component costs are due to an overall global shortage of parts. Everybody's in the same boat on that one. Don't know about France, but in the US there are lots of hobby suppliers. Jameco, Futurlec, Sparkfun, All Electronics, Circuit Specialists, and of course Digikey and Mouser. And eBay is a good source for bulk stuff like resistor and cap kits. Beware of fake chips, though. As for test equipment, it's no different than any other task: you'll need tools, and know how to use them.

[Infamy]

For PI detectors it is getting the coil fast enough to detect small and low conductive targets. This includes the cable from circuit to coil.

For VLF detectors it is getting the Exact inductance to resonant at the correct frequency. Then the Nulling of the Receiver coil is very, very touchy.

For both is creating an effective shield that doesn't decrease sensitivity.

Another issue many have is all the EMI in and around one's workshop that kills sensitivity and can create lots of false issues sending you on a wild goose chase.

Form here has lots and lots of posts about issues on building and tuning coil.

My workshop is partially insulated with reflective insulation. Although our wifi box is just in the next room I have to run a cable to the box because I have no signal. If I finish insulating the whole room I should have a low EMI environment, I also live in a rural are which must help too.

Do you know of any videos that run through these finer points of setting up a coil?

[waltr]

My workshop is partially insulated with reflective insulation. Although our wifi box is just in the next room I have to run a cable to the box because I have no signal. If I finish insulating the whole room I should have a low EMI environment, I also live in a rural are which must help too.

Do you know of any videos that run through these finer points of setting up a coil?

I haven't had issue with WIFI but in the winter my furnace produces lots of random EMI from its igniter (oil burner) and AC motors. Any testing I do then must be done when the furnace is not running. Other have had continuous EMI issues. So YMMV.

There is a good Russian video on Nulling the TGSL coil. But don't remember where the lick is.
Also, lots and lots of threads on coils building, tuning and shielding with videos. You just need to search and read.

[surfdetector]

Do you know of any videos that run through these finer points of setting up a coil?

The easiest coil to build for your PI is a bundle wound mono. Here is a link to an excellent article by bbsailor:
https://www.geotech1.com/pages/metde...s/FastCoil.pdf

[Infamy]

The easiest coil to build for your PI is a bundle wound mono. Here is a link to an excellent article by bbsailor:
https://www.geotech1.com/pages/metde...s/FastCoil.pdf

Thanks, I read most of the papers and forum stuff over tens years ago, just ended up doing other stuff instead. I find videos are better for the detail, less cracks to fall through. Some car part manufactures are now put out installation videos some detailed that the car manual is virtually redundant.

Every thought of going on to a paid subscription site?