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Originally posted by mikebg
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Analysis with 150 ohm resistor shows that when ear pieces are connected in series, they will sound about 3 dB more loud instead of parallel. That means in each ear piece flows about twice more current. -
Ok, thanks for advice.Originally posted by mikebg View Post
I'm actually not sure if there is a shield on my phones, but question was the same.
They are loud suckers without the resistor. I always put them above the ear to protect hearing, but I'll try resistor.
Interesting about "anti-phase", I hadn't thought about that -- probably wouldn't bother me -- but maybe nicer if target sounds like it is in front of you! (next idea -- using stereo effect to indicate location of target in ground -- some day)
Regards,
-SBComment
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curious
R54 (1M) and C24 (.022) are a curious part of the TGSL circuit.
Anyone have ideas on exactly why it is there? Has anyone tried removing it and merging C24 into C25 by using a .047u cap for C25?
Even though it looks like a pull-up, the real pull-up is done by U105 output through R40 (100k) I think.
An early TGSL circuit had 4.7K resistors separating U106 outputs from C24 -- then the circuit might have had a purpose in creating a slower shutoff of pulse.
I think Molzar checked original TGS and no 4.7K resistors though.
On another note: those extra resistors can be useful during tuning -- because they slightly isolate the LM393 outputs, and then you can check each LM393 output separately and see if they trigger at the same input threshold -- if not, you can consider replacing the LM393 for one with equal input thresholds.
-SBComment
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C9 modification
TGSL DISC control circuit has well-known behavior with jagged waveform at LF353 (U101b) output pin 1, sometimes causing break-up of sync pulse at low DISC pot settings.
This may not be a problem and is OK. But it seems bad.
A simple way to improve it may be to reduce the value of capacitor C9 (at inverting input pin 2 of LF353 U101b) from 100p to around 50p to 60p. You want a value that gives maximum output voltage without the jagged waveform. It depends on your TX oscillator voltage.
This should be simpler than the "SB mod" that I tried in TGSL Experiments thread, and no need to change PCB.
-SBComment
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Hi guys, I have some problems with my TGSL circuit, most likely the coil, but I dont know for sure.
My coils:
When nulled they are 26cm in diameter.
TX=5,77mH with 20,5nF for C2 at about 14,45kHz
RX=6,22mH with 15,1nF for RXC should be around 16,42kHz
Shielded with alu tape.
It detects a 4,5cm 1oz silver coin at around 10cm and 1e at around 8cm in AllMetal-Mode, very poor.
I replayed C9 with a resistor 100k, because the signal at U101b pin 1 was a very crippled sinus. (Tried with different ceramic caps, different qualities and different values like 68pf and 47pf)
Nulling is very strange. I disconnect RX and measure both ends with my scope while running TX. The sinus gets smaller and larger but I cant get past 7mV.
I also switched RX/TX starts and ends in many different ways and only one combination gave detection.
Unfortunatly only one channel and the external trigger are working at the moment, so i cant measure phase shift.
Could the porblem be in the circuit?Comment
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With external trigger on TX signal, I think you should be able to estimate phase shift of other signals, no?Originally posted by akademiker View Post
Can you take pictures of scope? Put external trigger on TX signal (J1-1), then show separate pics of TX signal, RX signal at LF353 pin 7, Sync pulses at JFet gates. Make sure you show the left edge of the signal, and also tell us where zero volts is on your scope screen. Don't readjust horizontal position between pictures so we can estimate the phase.
Show the sync pulses with the DISC and GB pots at minimum. Use DISC mode, not ALL METAL. Then rotate the pots and make sure both sync pulses move back and forth a little. DISC sync pulse should move around 80 to 90 deg, GB pulse around 30 to 45 deg.
Eventually, you will want to put your scope on very slow sweep (.05 Seconds / div) and look at your target pulse at output of LM358 and LM308 chips.
Post photos of your PCB and coils. Shields on coils can keep null large, not necessarily a problem. Double-check your shields have the "gap" in them and do not touch each other to make a continuous loop anywhere.
You can also look at troubleshooting thread for ideas and asking more questions.
http://www.geotech1.com/forums/showthread.php?t=16122
Regards,
-SBComment
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Shields have both a gap and dont touch each other except at the position connected to the cable.
What exactly do you mean with "Sync pulse" ? Which pins should i measure?
Also i dont know in which position my disc and gb pots are at minimum as i use external pots, what signal should be at the middle part of the pot when at minimum?Comment
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Thanks for pix.Originally posted by akademiker View Post
If you can make them a little smaller for viewing in future (720 horizontal prob good).
Which schematic did you build? Your first photo of TX signal looks very low voltage and does not have the "bump" like most TGSL. It is more like TGS schematic that has a JFet in the oscillator circuit.
Your second photo - is that LF353 pin 7? If so, it means your coils are not nulled at all. Try nulling them until signal is minimum, then push them together just a hair more until voltage rises a little from minimum (maybe 30%).
If you look at typical TGSL schematic, DISC sync pulse is output of U102a pin 1 (LM393 chip), and GB sync pulse is output U102b pin 7 (same LM393 chip).
Regards,
-SBComment
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it is a TGSL build according to http://www.geotech1.com/forums/showthread.php?t=15710
I tried to null the coils while measuring Pin 7 of LF353 and I couldnt get lower than an amplitude of 1,6V (Yes its not millivolts, but i guess its ok cuz it gets amplified, right?)
The syncs both show a nice sawblade and change their position a little. But when i turn the disc pot in the middle position the signal looks very strange and then is almost zero.Comment
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Hi akademiker:Originally posted by akademiker View Post
Your null voltage at pin 7 of LF353 may be OK. Shields and cables can cause a fairly large null.
Your GB sync pulse looks normal.
Your DISC sync pulse seems to have a problem -- it is shifting 180 deg instead of 90 deg.
I think your capacitor C9 (connected at LF353 pin 2) is "shorted" or too large. Would you show schematic of any mods you made there?
Use ohm meter and make sure C9 is not shorted. Make sure it is 100 pF or less, not 100 nF, etc.
Also we need to figure out why your TX voltage is so low. What are your V+ and V- voltages? What thickness wire used for TX coil? Can you double-check resistors in oscillator? Are you sure scale is 2 V/div in your photo?
Regards,
-SBComment
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I used a 100k resistor instead of C9, the sinus at pin 1 was horrible with 47pf 68pf and 100pf. Changing back to 100pf and taking pics. Now there is no more strange signal when in middle position.
I used 0.28mm wire in the coils the TX coil has 19,6 Ohm including usb-2 cable and the RX coil has 20,1 Ohm.
V+ is 12V and V- is 0V. I use a regulated power supply, so voltage is very stable. The circuit consumes around 30mA.
Yes I am sure its 2V/Div, my multimeter shows 3.9V AC too.
R1=2,2k ,R2=24k ,R3=47k and 2n2907 is flawless. What else should i check?
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Sorry, I meant the regulated V+ at the LM7808 output pin 3 (should be +8 Volts) and the negative supply rail (from Diode D6 and Capacitor C5, should be about -5 to -6.5 Volts).Originally posted by akademiker View PostI used a 100k resistor instead of C9, the sinus at pin 1 was horrible with 47pf 68pf and 100pf. Changing back to 100pf and taking pics. Now there is no more strange signal when in middle position.
I used 0.28mm wire in the coils the TX coil has 19,6 Ohm including usb-2 cable and the RX coil has 20,1 Ohm.
V+ is 12V and V- is 0V. I use a regulated power supply, so voltage is very stable. The circuit consumes around 30mA.
Yes I am sure its 2V/Div, my multimeter shows 3.9V AC too.
R1=2,2k ,R2=24k ,R3=47k and 2n2907 is flawless. What else should i check?
Easiest place to check is the V+ and V- pins of the IC's, see the schematics. They should all (except CD4024) show +8 volts on the V+ pin and approx -5 to -6.5 volts on the V- pin.
If your V+ and V- "rails" are correct voltage, let's concentrate on your oscillator section (TR1, C1, C2, R1, R2, R3). Something seems wrong there. Make sure values of parts are correct and transistor working OK -- I guess you already did that somewhat.
It is also possible something is draining current from your oscillator, like a solder bridge between traces. Check the resistance from J1-1 (same as TR1 collector) to ground. It should be really high, mine measured over 2 Meg.
If you have any extra coil approx 6 mH, disconnect your TX/RX coils and just connect the extra coil directly to oscillator and measure voltage. If possible disconnect the cable also. This is just in case you have some wiring problem in your cable or TX/RX coils.
Regards,
-SBComment
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V+ is 8V and V- is -6,7V.
Resistance from J1-1 to GND is around 15 Meg Ohms.
I connected an inductivity from an old tv around 7mH (3Ohms) and now it really shows 10V AC. Like it should be, right?
I disconnected everything and only connected the TX coil even without shielding with simple thick (1,5mm) wire directly to the oscillator but still only 4,8V AC. This drives me crazy.
In the Tuning &Troubleshooting thread Stefano's signal is around 8V AC, should it be in that range?Comment
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Nice job, it sounds like some problem in the TX coil.Originally posted by akademiker View PostV+ is 8V and V- is -6,7V.
Resistance from J1-1 to GND is around 15 Meg Ohms.
I connected an inductivity from an old tv around 7mH (3Ohms) and now it really shows 10V AC. Like it should be, right?
I disconnected everything and only connected the TX coil even without shielding with simple thick (1,5mm) wire directly to the oscillator but still only 4,8V AC. This drives me crazy.
In the Tuning &Troubleshooting thread Stefano's signal is around 8V AC, should it be in that range?
Your "rail" voltages are perfectly normal.
Scope trace is best for measuring TX signal, AC meters are all different.
Usually people get around 16 V peak-to-peak, so 10 V AC may be correct. When it is working properly you will usually see a small "bump" distortion on the TX signal and it will be about 16 v pp. Can you post photo of oscillator voltage with TV inductor?
Your oscillator frequency with your TX coil seems to be around 9 kHz looking at your scope trace. This is too low for the inductance you measured (5.77 mH). Of course assuming your Oscope is accurate.
Because the TV inductor seems to work correctly, it seems something funny is in your TX coil.
19.6 ohms seems OK for TX coil. Can you check again anyway?
Do you have a frequency meter?
What is the measured frequency of the oscillator with your TX coil, and also with the TV inductor?
Do you have an inductance meter? What is the inductance of your TX coil?
Did you put any kind of glue on your TX coil?
One suspicion is that some windings have short-circuited in the TX coil. But this does not make sense to me because I would think it would make resistance lower and frequency higher. But who knows...
Because the TV inductor works OK (we need to be sure), it seems something is wrong in your TX coil, and that is a good mystery.
The best way to check is to wind another one
.
Regards,
-SBComment
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Hi ,Originally posted by simonbaker View PostNice job, it sounds like some problem in the TX coil.
Your "rail" voltages are perfectly normal.
Scope trace is best for measuring TX signal, AC meters are all different.
Usually people get around 16 V peak-to-peak, so 10 V AC may be correct. When it is working properly you will usually see a small "bump" distortion on the TX signal and it will be about 16 v pp. Can you post photo of oscillator voltage with TV inductor?
Your oscillator frequency with your TX coil seems to be around 9 kHz looking at your scope trace. This is too low for the inductance you measured (5.77 mH). Of course assuming your Oscope is accurate.
Because the TV inductor seems to work correctly, it seems something funny is in your TX coil.
19.6 ohms seems OK for TX coil. Can you check again anyway?
Do you have a frequency meter?
What is the measured frequency of the oscillator with your TX coil, and also with the TV inductor?
Do you have an inductance meter? What is the inductance of your TX coil?
Did you put any kind of glue on your TX coil?
One suspicion is that some windings have short-circuited in the TX coil. But this does not make sense to me because I would think it would make resistance lower and frequency higher. But who knows...
Because the TV inductor works OK (we need to be sure), it seems something is wrong in your TX coil, and that is a good mystery.
The best way to check is to wind another one.
Regards,
-SB
Or try to connect your Rx coil on the Tx circuit .
This saves you some time in winding another coil
and it is another easy way to find out if the problem is in the coil or in the Tx part of your circuit.
You can also doublecheck and recalculate the values of your Rx coil given when connected to the Tx part.
http://www.whatcircuits.com/lc-reson...cy-calculator/
1. Enter desired f and C to calculate L (delete L before Calculate )
kind regards ,
Dennis the MennisComment
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