TGSL Experiments

[simonbaker]

Hello SB!

I played a little with my circuit today too.
I found reason why output voltege was lowering with input increasing - my sig gen fault. Its dutty cycle was changing when level was changed. Well it is DIY anyway Sine output is perfect at least.

I tried a small chokes in the output - didnt see improvements. Small oscillations appiered instead of sharp edges.Or Maby its better ?

I coded a fast pic code to generate 15.75Khz square and put it on the input. Output still 50Vp2p.

It connected other coil to the scope (10n parallel) and tried nulling and it looked very good. I could manage almoast zero null voltage. It was just fast and dirty test - didnt even remember actual numbers

One interesting thing. In ltspice this diode (see attachment) added 7V p2p (almoast 60Vp2p), but in real circuit it didnt make any difference. I dond know why. Even not shure what this diode does in sim?

I have one blank eduardo PCB. Maby it is worth trying solder one but instead of colpitts use this oscillator? But Im too lazy to solder right now . Its too early i think..

I found reason why output voltege was lowering with input increasing - my sig gen fault. Its dutty cycle was changing when level was changed. Well it is DIY anyway Sine output is perfect at least.

Aha! Sneaky.

I tried a small chokes in the output - didnt see improvements. Small oscillations appiered instead of sharp edges.Or Maby its better ?

I'm not sure either. I'll start without it for simplicity I think.

I coded a fast pic code to generate 15.75Khz square and put it on the input. Output still 50Vp2p.

It connected other coil to the scope (10n parallel) and tried nulling and it looked very good. I could manage almoast zero null voltage. It was just fast and dirty test - didnt even remember actual numbers

Good work, you're ahead of me -- but that is the idea exactly. I'm trying to get my protoboard layout of this circuit designed which will attach to the microcontroller Launchpad platform -- wasting a lot of time trying to think ahead of all possibilities I might need, such as other pins I will want to connect to on the microcontroller.

One interesting thing. In ltspice this diode (see attachment) added 7V p2p (almoast 60Vp2p), but in real circuit it didnt make any difference. I dond know why. Even not shure what this diode does in sim?

I tried duplicating your simulations, maybe not exact parameters as yours. I get about 60 V pp in your original circuit (R7 4k7, R1 1K), and about 70 V pp with your new "diode" circuit. One obvious difference is your diode circuit is driving the positive pulse though only 1K resistor instead of 1K + 4.7K, and your down pulse is sinking through zero ohms essentially -- so probably working the transistors harder but also using more current. It's still an interesting variation worth studying some more -- maybe an improvement.

I have one blank eduardo PCB. Maby it is worth trying solder one but instead of colpitts use this oscillator? But Im too lazy to solder right now . Its too early i think..

[/QUOTE]

You still need to make an oscillator, but maybe a simple relaxation oscillator or 555 chip. It would take some doing, but I'd definitely like to see what happens. If you end up with a higher TX voltage, you'd probably need to reduce the gain on the LF353 pre-amp to compensate. I hope you can get around to it.

Regards,

-SB

[simonbaker]

You still need to make an oscillator, but maybe a simple relaxation oscillator or 555 chip. It would take some doing, but I'd definitely like to see what happens. If you end up with a higher TX voltage, you'd probably need to reduce the gain on the LF353 pre-amp to compensate. I hope you can get around to it.

Regards,

-SB

Of course if you can fit the PIC on the board, don't need an oscillator! At least that would be a goal.

-SB

[habitbraker]

Hi,

I havent done any work regarding this lately. Its is such a good weather here that it is impossible to stay inside

what do you think about this voltage divider for negative supply and phase shifters?
Havent tested it in real yet.
Also I think that I will use some kind of analog oscillator to generate square signal. It would be easear/quicker to adjust for different L/C values. Also cheaper.
MCU would be nice to use if it is doing more things than only one.

[simonbaker]

Hi,

I havent done any work regarding this lately. Its is such a good weather here that it is impossible to stay inside

what do you think about this voltage divider for negative supply and phase shifters?
Havent tested it in real yet.
Also I think that I will use some kind of analog oscillator to generate square signal. It would be easear/quicker to adjust for different L/C values. Also cheaper.
MCU would be nice to use if it is doing more things than only one.

I agree, this work is best for rainy days.

Can you describe your voltage divider idea more? I'm not clear what you mean.

Regards,

-SB

[habitbraker]

I agree, this work is best for rainy days.

Can you describe your voltage divider idea more? I'm not clear what you mean.

Regards,

-SB

Well, my idea was to reduce voltage fed to phase shifters. Simple CC buffer to reduce divider output impedance. As I said - its just a idea and also not tested.

[simonbaker]

Well, my idea was to reduce voltage fed to phase shifters. Simple CC buffer to reduce divider output impedance. As I said - its just a idea and also not tested.

Makes sense. I can't quite tell what those supply voltages are on the CC buffer transistor, maybe V+ and V- basically?

You might not even need the CC buffer at all. Always looking for ways to reduce parts.

Regards,

-SB

[simonbaker]

big bang

Hi habitbraker:

In the coil-driver circuit we've been playing with, I keep wondering what is the optimal way to drive the coil.

With simulation, I compared two ways to orient the push-pull transistor -- emitters connected, or collectors connected.

It turns out if you use a low internal resistance voltage supply and a small resistor feeding the push-pull transistors, you can get a whopping coil voltage with the connected collector configuration.

However, it draws more current to do it, and I don't know if it is efficient power-wise. But if you really want high voltage it seems possible.

I haven't built it, not much time to tinker or think. Wondering if you had any opinion on it.

-SB

[habitbraker]

Hello SB!

Thanks for a new idea!! I played a little bit with spice (yet) and results were interesting! I got 80Vpp with my circuit (18ohm coil). That diode plays really huge role in output voltage(+/-20V depending).
Lowering Rl to 10 ohm gives about 120Vpp (I must get thicker wire to test this)

Also noticed that it depends on C and L values highly. I wonder if theres a math explanation about this.

Yeah - current consumption from 10mA went to about 60mA. Doesnt depend on Rl. A little drawback....

Now I have a short of time to tinker too. But this is defenitely on my MUST TEST list

Also wondering why I havent seen such a high voltage coils on other MD shematics around geotech? Could there be some hidden rocks ? Maby on field it simply doest work? Ground effect increased maby?

[habitbraker]

Makes sense. I can't quite tell what those supply voltages are on the CC buffer transistor, maybe V+ and V- basically?

You might not even need the CC buffer at all. Always looking for ways to reduce parts.

Regards,

-SB

Yeah those voltages is V+ and V- of tgsl (+8 and -6V).
Do you think I could get trough with simple divider?
If I remember correcly - you used one in order to reduce spikes? Was there other changes as well?

[simonbaker]

Hello SB!

Thanks for a new idea!! I played a little bit with spice (yet) and results were interesting! I got 80Vpp with my circuit (18ohm coil). That diode plays really huge role in output voltage(+/-20V depending).
Lowering Rl to 10 ohm gives about 120Vpp (I must get thicker wire to test this)

Also noticed that it depends on C and L values highly. I wonder if theres a math explanation about this.

Yeah - current consumption from 10mA went to about 60mA. Doesnt depend on Rl. A little drawback....

Now I have a short of time to tinker too. But this is defenitely on my MUST TEST list

Also wondering why I havent seen such a high voltage coils on other MD shematics around geotech? Could there be some hidden rocks ? Maby on field it simply doest work? Ground effect increased maby?

Yes, it's worth studying some more. Roughly, I see it like this: If the "parallel" capacitor with the coil is small compared to the "series" capacitor, the circuit is like a series resonant circuit. In this case, all the resistors in the circuit affect the Q of circuit, including the power supply internal resistance, feed resistor to the transistors, etc. So lowering those resistors can boost the Q and the coil voltage.

If the "parallel" capacitor is large compared to the "series" capacitor, then it acts more like a parallel resonant circuit, and the Q is determined more by the resistance of the coil only. Since a parallel resonant circuit has maximum impedance at resonance, the other components in the circuit have less effect on the coil voltage. Also, you can get a pretty high voltage even with a high-impedance power supply, meaning it runs efficiently.

I have same question about whether such a coil driver circuit has weakness in real practice. The answer is probably yes. High Q resonant circuits will be easily affected by ground, etc. The trick is to understand the effects and still be able to distinguish targets. With a good microprocessor, maybe can be done - which is why I like this circuit for microprocessor experiments.

It will be fun to find out what can be done.

-SB

[simonbaker]

Yeah those voltages is V+ and V- of tgsl (+8 and -6V).
Do you think I could get trough with simple divider?
If I remember correcly - you used one in order to reduce spikes? Was there other changes as well?

Yes, I used a divider, and I also needed to put a capacitor in also to correct for some phase shift because the divider makes a high impedance signal source. So your idea of transistor buffer is probably good, your instincts were correct I think.


-SB

[lunamay]

hi
i've got some questions

my pcb seems to be not good as i was thinking..the reason- i didn't clean it after soldering..i forgot..is there an easy way to clean this board with home made or in-home specyfics? i noticed that there was some posts about cleaning the board but i can't find them now..anyway..another thing is how to protect pcb tracks from oxidation using cheap specyfic..wood varnish or something..did anyone tried something like that?

About my TGSL..I'm still working. There is a lot of trubles to find time to experiment (on friday 17.06.2011 i will be trying to pass engeneer exam and that'll be the end of"school":P)

My unit will have baterypack(or acupack) on belt connected to unit by wires..still searching for a plastic for enclosier..and field tests.. but i'm wery happy that something is going on..some progres..slowly but is I should start from other detector Pi or something because i think that pi's are more easy to build and tune up good..aspecially coils(mono coils)

anyways..for tooday i wish you good luck with Your versions
see you soon
have a nice day/night ( OMG it's allmost midnight in my citty:P)

best regards

[simonbaker]

hi
i've got some questions

my pcb seems to be not good as i was thinking..the reason- i didn't clean it after soldering..i forgot..is there an easy way to clean this board with home made or in-home specyfics? i noticed that there was some posts about cleaning the board but i can't find them now..anyway..another thing is how to protect pcb tracks from oxidation using cheap specyfic..wood varnish or something..did anyone tried something like that?

About my TGSL..I'm still working. There is a lot of trubles to find time to experiment (on friday 17.06.2011 i will be trying to pass engeneer exam and that'll be the end of"school":P)

My unit will have baterypack(or acupack) on belt connected to unit by wires..still searching for a plastic for enclosier..and field tests.. but i'm wery happy that something is going on..some progres..slowly but is I should start from other detector Pi or something because i think that pi's are more easy to build and tune up good..aspecially coils(mono coils)

anyways..for tooday i wish you good luck with Your versions
see you soon
have a nice day/night ( OMG it's allmost midnight in my citty:P)

best regards

It's good to hear you are still working on it.

I don't know about cleaning boards but do a search, I remember some discussions were about it.

Maybe after you pass exam you can avoid job and play with TGSL for a while... right!

Good luck!

-SB

[porkluvr]

hi
i've got some questions

my pcb seems to be not good as i was thinking..the reason- i didn't clean it after soldering..i forgot..is there an easy way to clean this board with home made or in-home specyfics? i noticed that there was some posts about cleaning the board but i can't find them now..anyway..another thing is how to protect pcb tracks from oxidation using cheap specyfic..wood varnish or something..did anyone tried something like that?

best regards

For rosin or no-clean flux, clean your PCB with alcohol. Or you can use trichloroethane PCB cleaner from a spray can, but that is expensive and more toxic. Scrub with a soft bristle brush and blow it off with compressed air. Repeat, several times! Isopropyl alcohol - drugstore variety - works well. Get the 90% if you can find it.

If the flux you used is classified as water soluble, scrub with water, and then blow with compressed air. Use distilled water or filtered water unless you can get 'ionized water' (don't ask me where to get that).

Important: If you do not have a source of compressed air you should final rinse the board with alcohol, shake it a few times, and let drip dry or dab with paper towel and place near a fan. Unless you like to take chances, your PCB will need to sit for several hours before you apply power.

There are a variety of conformal coat products on the market. Some you spray on, and some you brush on. A conformal coating will protect the board from moisture and keep the tracks from oxidizing.

[habitbraker]

Hello SB and others!

I tested another circuit - with values exactly like in the picture. I put together 555 timer so that I can vary frequency more easely. Coil is my actual coil used in standart tgsl. Its shielded/potted and its good one. (35cm+)

Results were very good: output voltage over 100Vpp!!Ok -With Current consumption about 36mA...Match pretty good with simulation
Capacitor values is choosed to match frquency of tgsl - about 14.80kHz in my real circuit. In Spice its little higher. C3 must be prety large.

If I increase resonanse freq with decreasing C1/C2 I could get about 150Vpp but then freq is incorrect - above 20kHz. So must accept those 100V

Even though 555 vary its dutty cycle with varying R9 its seems that its no problem for output voltage.

ok, thats was my fast test/and its description. So many projects and so little time (this and also IGSL. )