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is this schematics close to your original Bandido
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Hmm not really... I'd love to find an older schematic though. I'm sure there was one back in the day.
I put the original TX on the TGSL today. The TX is 17V tall at 15khz. For the negative supply I got -7.6V!
I see a lot of noise on the sine wave though. I think my scope is getting funky on me. Both channels look
noisy even with no signal going in. I may bring it to work and check it on the scope there...Comment
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hit wrong replyComment
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Here are some schematic´s. Don´t know if they are older.Comment
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Those schematics are all about the same we are looking for one with LM358's and LM308's instead of 2262's.
Thanks for your help though!
SL3 is the Disc pot I think.Comment
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Well the mini H Bridge isn't working. I found a mixed transistor and fix that but still no joy!
Maybe the 3904's and 3906's Need a different resistance value?
I made up a mixed through hole/SMT Minelab oscillator today and it's working great!
I defiantly need some stable caps for the TX oscillator's. I got .47 and .22's from Mouser
not realizing I need .33 for the Minelab coil.
The TGSL is working with it's original oscillator for now. I'll do some testing before I change
it out (if I do). There are still some mods to the filters. I'm not sure if I will remove those for testing....Comment
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So I've been working on a big mod. I call it the Big Bandito and Tone Tune.
Here's the schematic;
It does a balanced TX and RX and has tunable dual tones via a level select able 4024 output.
Here's the first part I call it the sleeping H bridge as the transistors are laying down;
Here's the bottom. I'm using a special technique where some parts are through hole
(transistors) and some are SMT so as to make a tiny pcb.
It oscillates at 10 khz and has about 9V amplitude but that is hiding the fact that
there is around 150 ma in the coil! It only draws around 4 ma too!
The dual tone mod allows for all high tones, all low tones or switch from low to high at some amplitude...Comment
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Her's a dual oscillator setup. You need a 4 pole double throw switch as I'm not sure
what can still be connected when you switch over. Trying to save the 4ma the other
oscillator will use too. Not sure if I will use it as there will be a lot of wires...
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So my thoughts turn to packaging. I plan to use my old Tracker stick and housing but
not sure if I can use the coil. It has 2.4 mh TX and RX and a cap in the coil for TX to
run at 6.6 khz or so.
I don't know of any oscillator that would work with this setup. Maybe the IDX one?
I could also make a TGSL one or Minelab style and use the Minelab oscillator (as it
puts more current into the coil).
I made a metal plate for the control box and have to decide on what controls to include.
The so called "Sensitivity" control is really a threshold for the comparators. Some say it's
not too useful so maybe leave it as an internal trim pot? It's possible having 2 trims could
get you a more sensitive device too...
The threshold controls volume and with a simple mod can go from the stock setting to a
pure binary mode so could be useful to include.
The Disc is necessary and GEB is good to have too. So maybe Disc, GEB, Volume and a switch
for Disc/All Metal/Retune would be good? Oh a Tone control might be a good one too but needs
a SPDT switch to toggle the 4024 output but maybe we can make it work...
Anyone know a good free software package to design front panels? I've tried a couple but they
were tough to use. They either are CAD packages that need a long time to learn or are drawing
programs that have no built in designs. I just need something to make an oval panel and some
tick marks in a circle around each knob...Comment
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Well I tested the Tracker coil with the Minelab oscillator and HBridge oscillator.
I get 6 khz with the Minelab and 6.6 khz with the HBridge. Hmm to get up to
10 khz we need to reduce the capacitance and it's inside the coil housing...Comment
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Well I was getting ready to put the Bandito in a case but it has developed an instability.
If I probe to the input of the first filter it stabilizes. Must be an open somewhere near there?
I probed around a bit on the original Bandito too. I found the resistors on the outputs of the
comparators that compare metal and disc are 2k. It also uses back to back diodes on the final
stage. Here's a corrected schematic;
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It seems the instability is related to grounding the RX. I had similar trouble with my
TGSL and could not run it as a balanced input but had to ground one side of the RX.
I'm using the Tesoro coil now and the original Bandito works and is wired the same way
so I don't understand why the problem on the new board?
I just figured out the caps in the second filter were wrong on the original Bandito.
Here's a corrected schematic;
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I am confused with the center tap wiring
Found two diagrams but they are not the same
Very subtle difference one shows the center tap connected to both the TX ground and the cable shield.
This does not seem right to me as would cause a loop
Also both are missing the coil shield Tesoro use a conductive plastic would this not be connected to the cable shield then back to the board
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