HammerHead II rev D SMD specialized in prospecting for gold

[darov922]

A PI detector is made up of three parts: the electronic circuit, the coil and the firmware. I am now facing the second part. For the construction of the coil I chose a "patch cord" of 20 meters cat5 with a multicore cable of 1mm in diameter. Each wire has 7 copper wires and is very flexible to wind... It took 26 turns to get an inductance of 308 mH and 6.8 ohms of resistance. Dario

[darov922]

The detector has been tested with several types of coils... I have obtained in TX pulses of 550v amplitude and 2.5uS duration in the coil of the photo (300 uH, 7 Ohm and a damping resistance of 1200 Ohm) I have carried the frequency of the pulses at 3 khz and the consumption is 300 mA. However, despite this progress, I am still very far from being able to detect the gold nugget that is in the photo, I can barely detect my ring 10 cm away from the coil. I ask for help from anyone with experience with this detector to help me with ideas to increase the sensitivity. I also tried with half of an ETD49 core but there was no way to detect this small nugget of 4 mm in diameter...

should i use a different coil than mono?
make modifications in the RX circuit?
use cup type cores?
Increase the frequency up to 10 KHz?
use coils with lower inductance?

Dario

[waltr]

Only thing I can recommend is read through my HH2 thread.

Pay attention to pulse timing of TX and the two RX samples including EFE and GEB.

I have obtained in TX pulses of 550v amplitude and 2.5uS duration

Is 550V the fly back or the applied?
Is the 2.5uS the applied TX pulse or the fly back?

Is the above scope picture fro the coil or out of the preamp?

[darov922]

Only thing I can recommend is read through my HH2 thread.

Pay attention to pulse timing of TX and the two RX samples including EFE and GEB.


Is 550V the fly back or the applied?
Is the 2.5uS the applied TX pulse or the fly back?

Is the above scope picture fro the coil or out of the preamp?

First of all, Waltr, I appreciate your answer. I will read your version of HH2 carefully, regarding your doubts, here I present some images taken from the oscilloscope. The first image is the pulses taken directly from the coil with the corresponding measurements, the second shows the pulses introduced to the coil, the third image shows the output of the preamplifier (TP4) together with the first sample (TP5), the last image shows the output of the preamplifier together with the second sample... I have my doubts regarding the waveform delivered by the preamplifier... The first sample It is taken 4uS after the mosfet is turned off, it lasts 12 uS and the second sample is taken 215 uS and also lasts 12 uS.
Dario

[Carl-NC]

It looks like the preamp output clips at 300mV. That doesn't look right. What do the target signals looks like at the preamp output? At the demod output?

[darov922]

It looks like the preamp output clips at 300mV. That doesn't look right. What do the target signals looks like at the preamp output? At the demod output?

Thanks for your answer Carl, I also have my doubts regarding the output of the first stage of the opamp. Here I post images of the outputs of both stages of the preamplifier and the pulses after sampling (TP10 and TP11) I also changed from NE5532 to LT6231 and the curve looks different... I suspect that there may be some short circuit between the pins due to the pcb ( poorly attacked copper)

Dario

[Carl-NC]

None of this looks right. Measure the supplies, make sure they are right. Measure the (+) & (-) pins with no TX pulse, make sure they have correct DC levels.