Full m/lab SD2000 schematics

[doncaffe]

Hi Woody

Could you make some schematics of GP/X machines. I think on low noise stages and earth field cancellation stage. Of course and a filters. Just little drawings. I am very interesting in timing of those machines. Regards.

[turaj afshar]

hello plz help me ;plz send SD2000 original pbc .... for my emil [email protected] thanks my brother

[external9]

sd2000

helo Would explore how useful this is the metal detector?

[humhum]

sd2000 pcb pdf :
http://ultrashare.net/hosting/fl/f5f...roteus__V_6.95

[Mechanic]

Sd2000

Hi Humhum,

Check the coil preamp in the schematic pin2 lm394 connected to ground.

Also I note that there is no ground plane You need a big low impedance ground-plane. Make sure that the coil ground and your frontend receive ground are of the same plane and the preamp very close to the coil ground wire. There could be other errors also, I just had a quick skim

Cheers

[Mechanic]

Also after the receive circuit/integrators where is the filtering and audio? The front end fets are too far away from the coil ground. The track that carries the received signal is very long and will pick up all sorts of crap including switching noise from the 5+ supply. The receive wire should be separate to the coil hotwire so DD coils can be used.

[nejdet]

m/lab SD2000 schematics bi Sprint iayot50?

[nvs]

SD2000 Transmit circuit

What does the IRF710 and surrounded components (TLC271) in the transmit circuit of the SD2000.
Looks more or less like a parallel voltage stabilizer, but why?
- Does this limit the amplitude of the Flyback pulse?
- Does this serve to drive the fet switches in the frontend during the flybackpulses or is there even an other explanation.

And secondly I was wondering why a diode is placed between the tx-coil and the switching mosfets BUK455.

[Woody.au]

The comparator stabilizes the flyback voltage at a preset level and this will allow earlier sampling and also take into account the front end RX Fets are only rated to 200 volts and they see the Flyback voltage. Most Minelabs are limited to 185 volts flyback.

The diode is to remove the output capacitance of the TX fets effecting the capacitance of the RX circuit, it acts like capacitors in series so say 1000 pf of the Fets and 40 pf of the diode only = 48pf as seen by the RX stage.

[nvs]

SD2000 Transmit circuit

Hi Woody,

I was wondering why a comparator (and "a lot of" discrete components) is preferred over two anti-serie connected 185V zenerdiodes placed in parallel to the TX-coil? Another measure to keep capacitance at the RX-input stage as low as possible?

What's the impact of limiting the flyback pulse to 30V? Would make protection fets at the input of the RX-amplifier redundant?

[Woody.au]

The $50,000,000 question, is it the flyback that excites the target or is it the current ramp up into the coil? I have tried both raising and lowering the Flyback voltage but it seems to have ZERO effect on detection distance.

Bring it down too far and things get hot very quickly. I like your thinking on the removal of the RX switch, maybe someone can try and see what happens.

[Carl-NC]

I have tried both raising and lowering the Flyback voltage but it seems to have ZERO effect on detection distance.

You mean by adjusting the clamping circuit in the SD2000?

[Woody.au]

I should of said the clamp circuit.

[nvs]

To my opinion, depth depends on amount of energy the coil can transmit.
Amount of energy is limited by saturation of the coil (and of course by the electronics), where saturation is defined by the properties of a coil.
In case of a metaldetector the coil is not a wirewound coil: it has a core composed of soil and objects. Thus the properties of the coil are defined by the magnetic properties of soil and objects.

Since the flyback pulse is a result of the energy stored in coil and core,
quickly consuming that energy might enable a measurement window closer to the transmit pulse? This theory is partly confirmed by the test of Woody: clamping level does not affect the depth.

By the way, did someone ever measure the signal after the RX switch using a scope? This could give an indication on maximum clamping setpoint where a removal of the rx switches is still allowed?

[Mechanic]

The $50,000,000 question, is it the flyback that excites the target or is it the current ramp up into the coil? I have tried both raising and lowering the Flyback voltage but it seems to have ZERO effect on detection distance.

Bring it down too far and things get hot very quickly. I like your thinking on the removal of the RX switch, maybe someone can try and see what happens.

Hi Woody,

My belief in what excites the target is this, the peak current and the time that the higher current is present for and then how quickly this current stops. Of course this current has to be creating a magnetic field as efficiently as possible. The flyback voltage we see from the coil is a byproduct of the magnetic field collapsing. At the same time that the flyback is happening in the coil, there is also a flyback effect happening in the target and ground from the collapsing magnetic field. If the magnetic field is not present long enough to properly penetrate the target then the response from the target will be less.

Cheers