info baracuda kit

[green]

Are you sure the preamp output is settling at 0V?
From the scope shots it appears to be offset in the negative voltage direction.

STEP 5
RX preamp (see Fig. 7)
Fit R4 (1k), R5 (1M), R6 (100k trimmer), R7 (1k), R8 (22k), R9, R22 (27R), R16 (150R), R18 (10k), C2, C18 (47u), C3, C15, C19 (100n), D1, D2, D6, D7 (1N414 and U2 (NE5534)
Measure the DC voltage on U2 pin 6, and adjust R6 to give 0V

Step 5 needs to use a scope to set preamp output to zero volts.

[Qiaozhi]

ok Qiaozhi,I adjusted trimmer r6 for 0Volt off set pin6 U2, I am attaching oscilloscope images .ch1 U4 pin4 - ch2 U2pin6.
it all seems ok.
It could be a disorder of the LT1054 synchronous?
thank you
[ATTACH]38565[/ATTACH]
[ATTACH]38566[/ATTACH]

Are you sure the preamp output is settling at 0V?
From the scope shots it appears to be offset in the negative voltage direction.

[gallico58]

The normal threshold setting is somewhere near the middle. Have you adjusted the Null Offset pot correctly?
It might also be worth trying a 300uH coil, although 400uH should be just fine.
Can you post a scope shot with channel 1 connected to U4 pin4, and channel 2 connected to U2 pin6? Set the scope to trigger on channel 1.

ok Qiaozhi,I adjusted trimmer r6 for 0Volt off set pin6 U2, I am attaching oscilloscope images .ch1 U4 pin4 - ch2 U2pin6.
it all seems ok.
It could be a disorder of the LT1054 synchronous?
thank you

[Qiaozhi]

excuse my English translator, I try to explain.the circuit works well, I optimized the dumping resistance (400ohm), as you suggested.
the threshold when adjusted gets to a point that the metal emits an impulsive sound beeat .... beeat .... beeat ... until the true threshold.
this for a small stretch of adjustment of the potentiometer.
Not crazy I have to be at the limit of this swing is something missing in the sensitivity.
but perhaps it should be so, if I'm sorry, it's my first md pulse, I have to figure it out.

The normal threshold setting is somewhere near the middle. Have you adjusted the Null Offset pot correctly?
It might also be worth trying a 300uH coil, although 400uH should be just fine.
Can you post a scope shot with channel 1 connected to U4 pin4, and channel 2 connected to U2 pin6? Set the scope to trigger on channel 1.

[gallico58]

excuse my English translator, I try to explain.the circuit works well, I optimized the dumping resistance (400ohm), as you suggested.
the threshold when adjusted gets to a point that the metal emits an impulsive sound beeat .... beeat .... beeat ... until the true threshold.
this for a small stretch of adjustment of the potentiometer.
Not crazy I have to be at the limit of this swing is something missing in the sensitivity.
but perhaps it should be so, if I'm sorry, it's my first md pulse, I have to figure it out.

[Qiaozhi]

ok thanks I understand the procedure.

adjusting just before the threshold is a disorder such as motorcycle to a minimum that keeps me from going further.
being below that level it's all ok, quiet and functional.
verified the +5 -5 ok no ripple, 12v battery ok
it could be the cable unshielded coil connection?
eliminating this would earn something more like sensitivity.
any idea about it?
thanks to all

I thought you said you the detector was working well with good depth. Do you have a different problem?

[gallico58]

ok thanks I understand the procedure.

adjusting just before the threshold is a disorder such as motorcycle to a minimum that keeps me from going further.
being below that level it's all ok, quiet and functional.
verified the +5 -5 ok no ripple, 12v battery ok
it could be the cable unshielded coil connection?
eliminating this would earn something more like sensitivity.
any idea about it?
thanks to all

[Qiaozhi]

OK thanksI will follow your advice, as I understand When I reach the critical damping? The sets the preamp output as instructed to 0 volts in the absence targets, Which optimum waveform?
However, you are right, by adjusting the delay refuses small foils.
thank you for your advice, I have to understand

When the MOSFET is turned off, the voltage at the preamp output needs to decay to 0V as quickly as possible without oscillation. This is called critical damping.
http://hyperphysics.phy-astr.gsu.edu/hbase/oscda2.html

[kt315]

OK thanksI will follow your advice, as I understand When I reach the critical damping? The sets the preamp output as instructed to 0 volts in the absence targets, Which optimum waveform?
However, you are right, by adjusting the delay refuses small foils.
thank you for your advice, I have to understand

Maybe you should also read this ->
Inside the METAL DETECTOR - Second Edition - Published 2015

ISBN 978-0-9858342-1-0 (Also available for Kindle)

[gallico58]

OK thanksI will follow your advice, as I understand When I reach the critical damping? The sets the preamp output as instructed to 0 volts in the absence targets, Which optimum waveform?
However, you are right, by adjusting the delay refuses small foils.
thank you for your advice, I have to understand

[Qiaozhi]

thank you Quiaozhi
my mistake, the frequency is about 700Hz
theoretically increasing the delay should eliminate small aluminum objects.
I increased the dumping resistance 470ohm, let's see how it goes, however it has good depth, good product kit.
regards

Try this damping resistor adjustment tool:
10k pot in series with a 200R resistor, and a 2k resistor in parallel with both the pot and resistor. This will give you an adjustment range from 181R to 1672R.
Attach your oscilloscope to the output of the preamp, and adjust the pot until you achieve critical damping. Disconnect the adjustment tool and measure the final resistance. Replace with a fixed resistor that has the closest value.

[gallico58]

thank you Quiaozhi
my mistake, the frequency is about 700Hz
theoretically increasing the delay should eliminate small aluminum objects.
I increased the dumping resistance 470ohm, let's see how it goes, however it has good depth, good product kit.
regards

[Qiaozhi]

HelloI finished assembling the baracuda kit, no problem during installation, calibration seem ok from oscilloscope images.
the coil is 400uh 2omh.
the depth is good, the threshold goes well, I do not understand what is the delay adjustment, it does not change me absolutely nothing adjustment, it depth, it discrimination.
I do not understand what it's worth, those who help me? Grazie!!!

http://uploads.im/GBPaJ.jpg 700 khz pulse
http://uploads.im/OJmPS.jpg delay min
http://uploads.im/s2pQE.jpg delay max

The lowest delay setting achievable with your coil is around 20us, so that looks correct. If a PI can detect aluminium foil, then increasing the delay will eliminate the foil. Further increasing the delay will knock out pull tabs. Hopefully you're not expecting the Baracuda to discriminate against iron, as PIs discriminate targets based on conductivity.

By the way, your pulse rate cannot possibly be 700kHz. It looks more like 700Hz to me.

[kt315]

those who help me?

silverdog?

[gallico58]

HelloI finished assembling the baracuda kit, no problem during installation, calibration seem ok from oscilloscope images.
the coil is 400uh 2omh.
the depth is good, the threshold goes well, I do not understand what is the delay adjustment, it does not change me absolutely nothing adjustment, it depth, it discrimination.
I do not understand what it's worth, those who help me? Grazie!!!

http://uploads.im/GBPaJ.jpg 700 khz pulse
http://uploads.im/OJmPS.jpg delay min
http://uploads.im/s2pQE.jpg delay max