Underwater detector - build suggestion

[Ferric Toes]

Yes, and now that I know how the machine is, I am proud that I have a real garrett detector...sweet

Although the schematic is similar, it is not that of the Garrett XL500. It is a general circuit arrangement that was used (and copied) with modifications in various land and underwater detectors in the 1980's, but originated in my Irish company, Location Technology Ltd. The adaptation of this circuit was a project we did for Charles Garrett and was their first P.I. detector. It replaced the VLF unit they previously had for water hunting.

Where your circuit originated I do not know, but various things have been changed which make it rather different from the XL500, but it looks sound and should work well. It could benefit from a few upgrades though; initially, replace the 2N3055 with a Mosfet such as the IRF740 and the 709 with a 5534. The 5534 does not need the 3.3pf and 10pf capacitors to keep it stable.

Eric.

[blobber]

Thank you Eric for your information and suggestions.
While I was searching, I found the original files for Garrett XL-500 Pulse with Google. Is that correct?
Anyway, it seems for me the same function. Well, sensitivity with switch. Can you or someone explain the task of
LM358 or the other difference to the version, which I have made?

Fred


Garrett XL-500 Pulse.zip

[Ferric Toes]

Thank you Eric for your information and suggestions.
While I was searching, I found the original files for Garrett XL-500 Pulse with Google. Is that correct?
Anyway, it seems for me the same function. Well, sensitivity with switch. Can you or someone explain the task of
LM358 or the other difference to the version, which I have made?

Fred

Hi Fred,
Yes, that corresponds with the proper schematic.

The LM358 is a dual audio oscillator which Garrett added to give a warbling effect to the audio. Garrett called it 'mellotone'. On my official Garrett schematic the coil damping resistor was 150R rather than 1K0. 150R does seem a bit overdamped though and I would put 270R as nearer the optimum. If you make your own coils this value needs to be matched to the coil characteristics. For the 3140 and 741 you can substitute TL061 or TL062 for a dual package to run both functions. The 4016 is a quad switch which switches the meter from signal indication to battery voltage indication. 555 can now be Cmos type.
Your unit has a high pass filter which is the 3rd 324 stage where you have a 0.47uF capacitor on the input. This gives what is called a dynamic, motion mode, or self zeroing response. The XL500 does not have this.

Looking at the Minipulse Plus thread, I would think this would be a very good basis for a waterproof detector. Maybe it has been already suggested as I have not looked at all the posts. This has a better receiver front end and lots of other updates on a very similar circuit arrangement. It also has the high pass filter mentioned above.

Eric.

[CDI]

Just to give small opinion... i wanted vlf machine, cause water is non salt. That's lake and rivers where i wanna hunt. I think it should work without false signal's with 16 cm coil. I will use coil enclosure from one old BFO Whites detector, there i have top and bottom side where can be sprayed with graphite.
The main problem is waterproof switch and disc pot. How those thing's can be made waterproof?

[Ferric Toes]

Just to give small opinion... i wanted vlf machine, cause water is non salt. That's lake and rivers where i wanna hunt. I think it should work without false signal's with 16 cm coil. I will use coil enclosure from one old BFO Whites detector, there i have top and bottom side where can be sprayed with graphite.
The main problem is waterproof switch and disc pot. How those thing's can be made waterproof?

Look like we drifted way off your original question.
I used APEM Hexseals very successfully for shafts or rotary switches. Also they make a variety of toggle switch seals and sealed screws. I have used controls with nylon shafts and also nickel plated brass shafts, Stainless steel is best but pots and switches with this material are much more expensive. The fact it is fresh water searching helps, as you do not have the corrosion problems. Discard any shafts with scratches where the seal is in contact. A smear of silicone grease on the shaft makes things run smoothly. Zago is another company that make a wide range of waterproofing parts. http://www.switchboots.com

Eric.

[blobber]

Just to give small opinion... i wanted vlf machine, cause water is non salt. That's lake and rivers where i wanna hunt. I think it should work without false signal's with 16 cm coil. I will use coil enclosure from one old BFO Whites detector, there i have top and bottom side where can be sprayed with graphite.
The main problem is waterproof switch and disc pot. How those thing's can be made waterproof?

Yes CDI, Eric has right, as he said, that we drifted away, sorry for that trouble.
Well, this parts on this site are very professionell of course.
Not so as my ordinary parts from radiator valves, which I have used for pot sealant.

[blobber]

Hi Fred,
Yes, that corresponds with the proper schematic.

The LM358 is a dual audio oscillator which Garrett added to give a warbling effect to the audio. Garrett called it 'mellotone'. On my official Garrett schematic the coil damping resistor was 150R rather than 1K0. 150R does seem a bit overdamped though and I would put 270R as nearer the optimum. If you make your own coils this value needs to be matched to the coil characteristics. For the 3140 and 741 you can substitute TL061 or TL062 for a dual package to run both functions. The 4016 is a quad switch which switches the meter from signal indication to battery voltage indication. 555 can now be Cmos type.
Your unit has a high pass filter which is the 3rd 324 stage where you have a 0.47uF capacitor on the input. This gives what is called a dynamic, motion mode, or self zeroing response. The XL500 does not have this.

Looking at the Minipulse Plus thread, I would think this would be a very good basis for a waterproof detector. Maybe it has been already suggested as I have not looked at all the posts. This has a better receiver front end and lots of other updates on a very similar circuit arrangement. It also has the high pass filter mentioned above.

Eric.

Many thanks you for you time and explanations, they are very helpful.

Fred

[kt315]

use search option and you will find much info on waterresistance tech. those questions are standing up with every
new member but all eggs would be setted in one basket. no sense to open new threads if there are oldier ones.

http://www.geotech1.com/forums/showt...ght=waterproof

[reptooyep]

Hi,
About underwater, does the surfpi 1.2 from silverdog mounted in a waterproof enclosure willdo the job ?
I hask this cause i want to purchase this board for the same purpose (the size is to big to etch by myself cause i have only 16cm board and the layout is 17).
Thanks

[CDI]

Hi,
About underwater, does the surfpi 1.2 from silverdog mounted in a waterproof enclosure willdo the job ?
I hask this cause i want to purchase this board for the same purpose (the size is to big to etch by myself cause i have only 16cm board and the layout is 17).
Thanks

Will do for sure, but in my situation, i need little discrimination. Surf or Barracuda will be better if u hunt in salt water.

[CDI]

use search option and you will find much info on waterresistance tech. those questions are standing up with every
new member but all eggs would be setted in one basket. no sense to open new threads if there are oldier ones.

http://www.geotech1.com/forums/showt...ght=waterproof

Sorry Kt dude, but i didn't found answer on my question's from other thread's. Btw, sorry again, i'm old member as u can see join date, just not active too much.
Regards

[blobber]

Hi CDI
Look for the Goldfish project from Merc

http://www.geotech1.com/forums/showt...ht=water+proof

but for the pots you need a separate solution

[godigit1]

Hi CDI
For the switch you can use a magnetic switch or make a diaphram for a rocker switch. The pots can be magnetically controlled, I used levers and roller bearings attached to knobs inside my case. Its not the prettyiest but it is fully functional and adjusts easily. Only thing is you need allot of room inside your case for this. I had to build my battery pack into the shaft. This was my first water proff detector and if I did it again I would use the magnetic switch instead of the diaphram beacuse you then only need two holes in your case for the coil and headphones.
The MPP I did this to is #11 on the MPP finished builds thread.

[kt315]

Sorry Kt dude, but i didn't found answer on my question's from other thread's. Btw, sorry again, i'm old member as u can see join date, just not active too much.
Regards

ok. i open old thread to fill it up by new content. http://www.geotech1.com/forums/showt...(pulse)-XL-500

[CDI]

ok. i open old thread to fill it up by new content. http://www.geotech1.com/forums/showt...(pulse)-XL-500

Thank's. Noticed that today.