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Tesoro Lobo Hijack


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I just recently got one of these Russian boards, which IMO looks like a good piece to work with. I read over the supplied build instructions which are fairly clear, but in a way are not totally, at the same time. I have worked with circuits quite a lot over several years, I went back to a site that discusses working with timer IC's of which in this build uses the 7555, a CMOS version of the vaunted 555 that uses 1/10th the power. This is where the MD transmitter freq. is produced. There are several ways to construct the oscillator and in the case of this design, I find one very small issue. Since as I mentioned, I just got this board and still working at putting it together, obviously I haven't tested it. Here is what I am here to discuss with anyone looking at this version, thinking about building one, or has one working. The 555 system has been know to experience unstable responses if there is no Capacitor connected from pin 5 to ground ! There is no Cap to pin 5 included in this circuit design and it uses a few other features that differ from the basic osc. circuits  A .01ufd cap which on this board can be installed on the back side of the board from pin 5 to the nearest ground buss and should be some improvement to the function and stability of the circuit, it is 'optional' and it will work without it. It is a very small mod but in my experience sometimes that is all it take to work or not. I also suggest to use .100 inch header pins for connecting any of the peripheral parts. Doing this makes it easier to R&R the board for working on it, you will need to be extra diligent about connecting everything back in the proper place but if you have gone this far with this project, that is a no brainer. There are a couple of places the .100 header pins will not fit perfectly but you can get around that with the use of a single break away pin and just a tiny bit of force to re align so your connection will fit as you continue assembly. 3 pins on the right of the rough GB Pot on board are one place, another is the 2 holes just to the right and above the 4 large elect. caps around the Vreg, LM7808 or LM7809, also using a 7809 might give you a slight bit of bump in performance. Since the circuit uses a +12v supply battery, there is still a bit of margin left so that the dropout V is going to remain above the output V of the regulator until batteries are getting too low. Using a battery carrier that holds 8 AA cells, alk or even NiM rechargeables will or should work and you should still be able to get this inside the housing. The use of NiM may exhibit an issue with the 7809 so make the choice based on what battery V you plan on using. One could also use an extra bat pack in series to push the V higher for the input, as the 78xx can handle up to 30v input, this will give you a lot more operation time before the dropout V becomes an issue. I would also think installing some reverse polarity protection here, 'NEVER a bad addition to any circuit and simple, a couple of small diodes and a fuse added to the project, around a 200 milliamp mini fuse is a good rating, put some extras inside the case. The current draw of this unit is very low so you can run your batteries way down this way and still keep going, having a small solar setup would be a good thing to have with you to boost batteries also, you could make it to fit over your hat!!! I am in the U.S. and have considered doing assembly of projects in the future,,, if my board works out. The one good thing I like about this system is that it should work with several different coils out there and one can even construct their own coil if using careful attention. Coils are really not that hard to make if you have and follow the instructions. Making the casing is probably the worst part of it, using resins and hardeners. Shielding is a bit critical here. I will mention that it is almost essential that you have an oscilliscope to build one of these for adjusting the timer section freq. the 5k pot on the left side of the 7555 and also setting amplitude on the upper right of 7555, the one just left of the 14 pin IC spot.. If you don't have a scope, there are apps online that make your PC work as one and you will have to learn how to use it, or get someone that knows to help with it. Also a transistor tester is helpful and when working with these parts, you MUST know the pins and install them RIGHT if you intend to have it work but you already know this if you are thinking about assembling one. 

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On 1/3/2019 at 5:14 AM, Lobo Lover said:

Hello everyone, 

                           I have just joined up and this is my very first post. I'm surprised to see fellow detectorists here from New Zealand. I've been here in N.Z. for almost 12 years now and only bumped into one other detectorist just a little while ago, some newbie from Christchurch going back home after his first trip to    Kyeburn Diggings up Dansey's Pass. Some older dude with his new Gold Monster 1000, he stopped off at the beach here in Timaru for a snack and his afternoon nap. No luck for him this time and he was complaining about all the metal the old time miners chucked about there. That's along drive to about 2.5 Hrs one way. We were just heading home after hanging out there for the afternoon, when he saw us just after testing out my wife's new BH Commando TK4. So we had a little bit of a tail-gate meeting with him. He wanted to showed us his GM 1000, it was nice to have a look at one up close and I took it for a bit of spin in the dunes. 

Anyway I'm not here to chat about new acquaintances, got much more important stuff to talk about. I would like to Hyper-Tune or Super-Tune my Lobo ST and  need some help with it. I Was thinking about putting on an external ground balance potentiometer to get some more depth, but first I need to know how it all works. Because my wife and I are Newbie's too and I'm trying to teach myself, my beautiful and talented assistant the "wife" all the ropes about MDing.

So if anyone can help in anyway it would be very much appreciated.  A German guy did that to his Lobo and he seams to be happy with his mod I think his name is mschahl and another guy Keith they both seem to very knowledgeable about the Lobo ST.  I would love to here about what is and isn't, the up and down's, the in's and out's and what mod's I could do with these two MD's the Lobo and BH TK4.

Also I could get a new PCB for the Lobo and put it in a build box like the one shown or drop it straight into the Lobo but don't know where or who could build it for me. This way I can take out the factory one to keep for a back-up incase anything goes wrong with my build. 

                                                                           Thanks' in advance for all your help and it's nice to be here, I don't feel so lost now.

                                                                                                                                                                                     Paul

Lobo complete.jpg

Just recently joined here myself and also recently acquired one of these boards. If you're still looking for help I can assemble board. I have a few ideas for bumping it up slightly and posted a somewhat long entry. Haven't seen it up here yet to see if it looks good, if it needs editing? 

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Is it possible to build one of those and have it run at 40khz-60khz? How difficult would that be?

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Ok I just joined this site earlier today and I am having issues getting where I want to go. I think I may have hijacked someones post and if this gets where I want it to go, I appologise. I just read a new post by KAJ asking if the circuit could be modified to run at a much higher frequency. I would like to tell him that I believe it could be set to run about anywhere provided the correct components where installed on the circuit board to enable the 7555 to generate the desired freq. simply by replacing the resistors and capacitor with the values needed to adjust the timing of the IC.

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  • 7 months later...

I forgot to mention a neat little piece of test gear that makes working with electronics much less hassle. The little GM328 transistor tester, which tests about every standard component one would work with. Transistors, MOSFET's, Capacitors, Resistors, Diodes, and Zeners up to 9 V, Inductors, and it identifies component leads and values. It will tell you what something is if you cannot identify it by the numbers or color code. Frankly I don't know how I got along without this device this long. It uses AVR C++ code running on a ATmega 328 controller with LCD display. The tester comes in kit or assembled, it is very cheaply priced for what it does. Get one just for the fun of having one, if you get one of the DSO's online plus your digital multimeter you have just about all you need for home hobby electronics.  

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