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ok, I just finished editing this on my floor so tgsl cms, so I added the CD4053 and the two 4.7k resistors for the moment it does not work, I have a permanent beep. es that quelq'un could put the pin numbers of the CD4053 in the diagram, I can be tricked into wiring am. thank you
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Here's a schematic with pin numbers on the second piece of the 4053. That's a fake part so you cannot do
a layout with it as drawn. I was just using it to draw the schematic.
My board wasn't working so I spent a week fixing it. It was falsing a lot but had worked for about 3 minutes.
It turned out to be "fake" LM308's from Ebay! I put some OP07's in and am ready to go now!
I wound a new TX last night with 45 turns of 24 AWG but the Minelab oscilator wouldn't oscillate with it. I'll
try it tonight with the H Bridge. I put an inductor on it at work with 1mh and it oscillates fine. The inductance
must be off. I'm still waiting for my $10 LCR meter fron HC (was due last week).Comment
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hello, I modified as you have indicate on your schematic, maintaining my detector thus does not emit more beep for the moment I think that on the level of wiring there is an error.Comment
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This is not a fully functional unit. It is a bunch of mods I am attempting to add to my TGSL.
I am having trouble with the H bridge oscillator. It only puts out 1V with the 150 ohm resistors
in circuit. I shorted them out and it worked but it was drawing 39 ma!
There must be something wrong. I pinned out all the resistors and checked the transistors were
still good. I even checked the caps (incircuit) but I still cannot get it to work again....Comment
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The Clapp configuration was more of a concept than a real attempt to make such oscillator. It could work provided the coil has solid Q factor, which is not the case with most of the coils around. So the best option is to make a simple H-bridge oscillator without Clapp capacitors. Besides, if you use electrolytes there, you have to use low ESR capacitors, otherwise you are reducing Q to abysmally low levels. Hence high consumption. Always use some emitter degeneration, at least 10ohm to reduce extreme currents.
Clapp is a way to increase voltage across a coil on expense of reducing a tank Q, so for a practical use just avoid it for now. You can try my new H-bridge oscillator with AB -> C approach instead. It is a bit more complicated, but it's signal purity should be superb, and power consumption ridiculously small.
I'll try to design a better phase shifting circuitry today so that you can replace the TGSL solution. With H-bridge you have a balanced signal at your disposal, so why not benefiting from it
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Yes I found it didn't work with the 3u caps. I tried reducing the current draw by changing the 47K's to
100K. In the sim it worked fine with those and the 680n's changed to 470n. Now it seems to have trouble
starting, maybe it needs a little imbalance? I'll try to reconfigure it to the AB/C and see what happens!Comment
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Here's a zip file with the SCH file (ExpressPC).Comment
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Well I got the new H bridge oscillator running today. It draws 6 ma (195mv across 33 ohm resistor) but
the voltage is just over 9v and the frequency is 10 khz. I got 8.6 khz off the Minelab oscillator (and 16v).
Davor is there any way to tune the frequency and voltage? I noticed the spice file had a variable for the 150K's...Comment
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I found that changing the caps from 470n to 680n changed my frequency to 8.6 khz but the peak voltage
on the coil decreased. Funny the sim didn't show that happening. I got the original H Bridge circuit working too
and it does the same thing. I'm just looking for the most bang for my buck. I wonder if I can get 12 khz out of
it as I have read that is the best all around frequency for MD's...Comment
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So here are the schematics of the 2 H bridges I am testing. I'm using the 1.0 mH spec from the Minelab coil (not
sure when where why it changed to 1.4 mH)
I have no current meter so am measuring the voltage drop across on 33 ohm resistor. The original 150's in the old
schematic reduced my output to 1V so they were originally shorted but now are 33 ohms.
Measurements;
Old H Bridge
8.6 Khz
7.3v
185 mv across 33 ohms (5.6 ma)
New development - - I added a 220u cap before the 33 ohm on positive side as I figured it might be running out of current.
Now I measure 15 mv across the 33 ohm -- That's 0.5 ma....
H Bridge AB/C
8.6 Khz
8.6v
223 mv across 33 ohm (6.7 ma)
(scope probe to one side of coil gnd to other side)
I'm not sure it is switching from AB to C...Comment
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That 1.4mH is simply inductance of my test coil that I often use for such designs - nothing else. Please note that some of my designs have a coil resistance listed inside the coil properties, and are not seen from outside. For coils in 1mH range this resistance is ~2.4ohm with a coil wound using 0.55mm diameter annealed wire. This is important because it determines the coil Q factor. At 8kHz Q is about 15, and it rises with frequency, hence you get larger amplitude at 10kHz.
As for AB->C just see the waveform across the 33ohm resistor, and you'll know. In case you observe overshoots (negative currents) then increase those 33ohm to some higher value.
Choice of frequency is up to you, and your choice of coils. You may go for 12kHz, only be sure to adjust Rx accordingly. Many people prefer commercial coils - I don't - so if you are after some degree of popularity of your design, just keep the original specs in mind, and don't change frequency for more than + or - 50% (to make sure coil balance is OK)
Otherwise, I like your Tx waveform - looks perfect!Comment
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I'm just looking to optimize my metal detector. On that note, I found this web site that talks about
tuning the TX and RX. It's in russian and a bit hard to follow; http://www.phazitron.com/article/sloop.html
I tried making a simulation but got a bit lost. Using the 1 mH and 14.7 mH specs forthe Minelab coil how would
you optimize the coils? I have the H bridge amplifiers. I could tune one to 8.7 Khz and tune the RX to 10.7 Khz
but wonder if some sort of "peaking" might give me a bit more depth? I don't really understand the factors involved
in choosing a RX frequency for nonresonant...
I seem to get different numbers each time I test the H bridge's but they put a lot of current into the
coil and have a nice clean waveform. So I'll use one of them for the finished MD.Comment
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I'm trying to finalize the TX and will go with one of the H bridges. I'm rebuilding
the old H Bridge into the New H Bridge as seem on the attached schematic. I'll
go with the one that puts a lot of current into the coil but doesn't use too much
juice.Comment
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Don't rush it
I'm itching to see how the latest H-bridge performs in real life, because it's sims are just superb. It provides everything.
Today I was in my lab ... for about 5 minutes
I so wish to spend much more time there.
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Here's the pics of the PCB and O scope display. Channel 2 is a current probe on one wire going to coil but it doesn't
seem to be reading correctly (should be 2ma per mv so 20mv = 40ma? ) . I'll check the current at work tomorrow.
The sine is by probing to one side of the coil and grounding to the other....
Hmm I just noticed I forgot R55 and C2 (for tuning gain), I'll have to add them tomorrow.Comment
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