TGSL Field Test

[Jerry]

Finished another 8 inch DD coil today so I took the TGSL out into the real world for about two hours and was pleasantly surprised at how well it performed. I have done a lot of testing in my test garden in the past but this is my first real hunt with the TGSL.

The new coil has mylar shielding and the connections are for the "wet grass" configuration.

I ground balanced to a piece of ferrite which is shown in the upper right of the picture with the plate of coins. I put this chunk of ferrite on the ground and increased the GEB until the signal is breaking up badly but not completely gone.

One observation I made is that U. S. Nickels hit really hard and have a nice fat signal. However Quarters are much shorter and clipped sounding. It behaved the same way on the test bench. I would be interested in feed back on what others who have used TGSL on the differences in how nickels and quarters sound.

I did add a threshold control to the front panel but I need to make some changes because I am not able to turn the op amp all the way on under no target signal conditions to get a steady tone. As it is, I had the threshold wide open (Most sensitive) and the sensitivity control backed off so that the detector was stable with minimum or no chatters. I can probably live with this but I would like to get it to the point where I can have a steady background tone to listen to.

We hunted at a skate park for skate boarders. The majority of the coins found were within very easy "coin popping" with a screw driver. It took a while to get used to the fact that there is no pinpoint button on the TGSL. However pinpointing is very easy and accurate. I just wiggle the target right up to the tip of the coil until it stops beeping and the coin is right at the edge of the coil.

Was not a huge day for dollar amount but I found 60 coins totaling $2.23 plus a huge pocket full of the aluminum junk. Not bad for two hours.

Jerry

[wallker]

Hi Jerry, could you tell us more about your coil (wire diameter, number of turns...) ?
Regards
Marko.

[Jerry]

Hi Marko,

The TX coil has 123 turns of 30 AWG wire and the RX coil has 130. Rather than measure inductance, I wound each coil to the exact frequency I wanted by measuring the frequency of the coil while still on the former. I made up a TGSL oscillator and power supply circuit on a test board several years ago and find many uses for it.

Here are a few pics of the coil winding setup. The former is a sandwich of paneling with a thinner piece of plastic in the middle. I used nylon screws to hold it together. The reason for this is to not have any metal in close proximity of the coil.

I test for proper frequency with the oscillator board as shown in the pictures. I remove just enough insulation so the clip lead makes contact. I started out by winding more turns than needed, testing, cutting a few turns off, testing again, etc. I found out that it more than accurate enough to just leave it connected to the spool. After the final frequency was reached, it did not change by more than 50 cycles after it was cut. Saves a lot of time.

Also as I am winding, I stop from time to time and dribble in some epoxy. When I am finished winding, I leave it in the former until the epoxy cures. This makes a very nice clean coil. Now I just need to find a neater way of applying the mylar and tape

I did not take any pictures while I was taping and putting the mylar on but at least there is one shot of the coils.

The reason one is white in appearance is teflon tape was used on the former for that coil. After that I used black PVC electrical tape. I have since bought a roll of White tape so it is easier to see the wire as it is being wound.

The over sized calculator works great for counting turns. Odd setup but it works.

Hope this answers your question.

Jerry

[dfbowers]

Dang, you are the master of innovation when it comes to keeping track of how many turns you have on your former . I think those 8" coils work pretty well with the TGSL. It really pays to invest in a good winding setup!



Mine at least has 10" of range for most coins. Here is that last one that I made for someone :
http://www.youtube.com/watch?v=pVEmB15VIYc

The sound is a little out of sync but I think it's just Youtube.

[Jerry]

Hi Don,

Well I got the idea for the 8 inch coil from posts that you have made in the past. I am getting pretty much the same results as your You Tube video. Goes to show that the information that you have shared does work

I did learn one thing this afternoon, this setup is very sensitive, I could not get within 18 inches of a chain link fence. Did not think much about it until wife covered the same ground with her Ace 250 with 10X12 coil and picked up two quarters about 8 inches from the same fence. Next time I got out I am going to experiment with the sensitivity control and see how close I can get to a fence and still pick up coins.

Jerry

[joop]

I like the coil winding setup, especially the coil winding counter! Thanks for sharing

[wallker]

Thanks Jerry
Regards from Serbia.

[Jerry]

I like the coil winding setup, especially the coil winding counter! Thanks for sharing

Thank you. Here are a few closer pics that will show better detail.


Jerry

[satdaveuk]

Nice setup mate, the calculator has got to be the most easest and cheapest way of counting turns yet some here seem to shy away from it.
You know i think im the only one on here thats actually winding coils on a horizontal motorized plinth.
Do you recon theres any advantage of running vertical?
check my posts and look at my rig that i made mid last year out of my junk box, it works great and i can make anysize coil shap or form, and same as your use of calculator switched by a reed switch.
If theres advantage in vertical i can easily mod mine, even noticed Tesoro run vertical so there must be something in it.
Your rig as it stands is begging to be motorized, if you want to know how, will give you some easy tips from my experience.

Regards

[satdaveuk]

heres a sterling silver bracelet i found late last year with my first TGSL build , had disc on disc pot minium 8" down in clay, woods, its not that old, came sweet as a nut same as large foil

[Jerry]

Hi satdaveuk,

My only rational for making the coil winder vertical vs horizontal is to make it easier for me to actually see the wire as it is being wound onto the former. My first winder was horizontal.

I remember your posts from last year. I did use a reed switch and magnet for a while to drive a mechanical counter that I happened to have in my junk box. I went away from that in favor of the calculator for several reasons. I was getting contact bounce and false reading on the mechanical counter. I did dampen down so it was fairly accurate but it would still glitch once in a while. The calculator is dead on for accuracy. Also I wanted to get as much metal away from close proximity to the coil as I could so I can measure frequency while the coil is in the former.

My mechanical finger for pushing the calculator button is admittedly crude but it has the added advantage of being able to use any calculator that I can position under the finger.

That is an awesome bracelet!

Maybe we should start a TGSL Finds thread for everyone to show what they are finding.

Jerry

[satdaveuk]

Hi Jerry
Yes thats the downfall with my design far as with the motor and drive shaft directly below the coil form can do a ruff estimate of inductance value then need to lift off the form and do the rest by hand, although theres normally only 2-3 turns either way.
far as using a read switch you only need to run a thin 2 core cable into the calculator and wire neg and the = pad to the switch and job done, the calculator can still be used as normal.
The important tip is dont try and solder to the pad cause you will knacker it, just stick it with some tape.
Saying that mind you yours does the job and i like your oscillator pcb.

Good idea about the TGSL finds thread, why not start it up and see how it goes.

All the best

Dave

[satdaveuk]

Hi Jerry
Yes thats the downfall with my design far as with the motor and drive shaft directly below the coil form can do a ruff estimate of inductance value then need to lift off the form and do the rest by hand, although theres normally only 2-3 turns either way.
far as using a reed switch you only need to run a thin 2 core cable into the calculator and wire neg and the = pad to the switch and job done, the calculator can still be used as normal.
The important tip is dont try and solder to the pad cause you will knacker it, just stick it with some tape.
Saying that mind you yours does the job and i like your oscillator pcb.

Good idea about the TGSL finds thread, why not start it up and see how it goes.

All the best

Dave

I ment Reed switch, me and my spelling

[Jerry]

Hi Jerry

The important tip is dont try and solder to the pad cause you will knacker it, just stick it with some tape.
Saying that mind you yours does the job and i like your oscillator pcb.

Good idea about the TGSL finds thread, why not start it up and see how it goes.

All the best

Dave

Hi Dave,

I did take a few calculators apart and looked at the keypads from the inside back when you made your postings on the subject but I decided for the mechanical option because I could see that there was no way of making a solder connection.

Now I am going to go back and give the tape idea a try. Good input.

We are headed out for another hunt for the afternoon, but I do have a discrimination question to pose later on when I can word it properly.

Just may start up a finds thread, that should be interesting.

Jerry

[Jerry]

TGSL Discrimination range.

I have spent the last week using my TGSL for actual metal detecting and learning the characteristics of a new machine. The detector works very well. Deepest coins I have dug so far were nickels at about six inches deep and they still gave loud and clear signals. Many pieces of junk were found much deeper so depth is not a problem.

The discrimination works well and I can ID the target most of the time by seeing how far the disc knob turns before beep tone goes away. It will discriminate out foil, nickels, pull tabs and ring type pull tabs as the DISC knob is rotated clockwise. It will not silence zinc or copper pennies, dimes or quarters when the DISC knob is turned to it's limits. This is not a big problem for me since that is what I am looking for but it It would be nice to be able to tell the difference between the zinc copper pennies.

My question is this normal for the TGSL or should it be capable of discriminating out zinc or copper pennies?

Jerry