Full m/lab SD2000 schematics

[ZED]

Front end receive gates

Hi Kev

The logic cct is good in itself in terms of generating pulses but it does not lend itself
very well when it comes to trying to change pulse widths or creating extra pulses not
to mention moving pulses about the place.

A MCU would be the ticket provided you had the flexibility to modify pulses or create
extra pulses,especially out on the field,plus the MCU would need to be able to generate
more than one pulse at exactly the same time.????,,,,not exactly a high point with sequential critters.
Could explain why m/lab dont use a MCU to generate there pulse trains.

The pic below shows the pulse train for the front end receive fets,both fets open and close at the same time,the cct that controls the front end receive fets gets its signal from the logic cct {same signal as the trans cct},the signal goes into a R/C circuit so as to create a delay,this R/C cct is also controlled
by other ccts,the delay is used to prevent the front end receive fets opening during the high voltage
fly back,this is my interpretation anyway.

Zed

[bugwhiskers]

Hi Guys,

Firstly let me thank Zed for his admirable work in unveiling one of the great PI mysteries.

I believe the small signal fets are there to blank the input so the pre-amp never goes into saturation which can cost several of the all important early microseconds to recover thus maximising the signal from small targets.

On your timings sheet Zed you show a figure of 300uS delay to the final ground channel sample. The timing figure should be from the last of the short 60uS pulses as it is providing the energisation for that sample.

regards
bugwhiskers

Made a booboo

Hi ZED,
I meant to say above that maybe one FET is on after the large pulse, while the other is on after the short pulses, do you know?

Regards
Kev.

Excellant work

Thank you ZED et al, for sharing this.

I think it would be good to replace the logic circuitry with a micro, so as to allow longer pulses without lengthening sample, and delay times, but not quite sure at this stage what the signals driving the input FETs E, & F, look like. It will take sometime to unravel the Tx block. I suspect that they are turned off during the pulse and flyback power scavenging time, and turned on at other times. Could it be that one is on during large pulse and the other on during the short pulses? Do you Kow ZED.

Cheers mate.
Kev.

[ZED]

Yummy paint

Sorry FOMA,m/lab like to paint there boards.

Zed

[FOMA]

HI ZED.
To do LAY, necessary such photo for SD2000.
To was seen tracks.

[ZED]

Hello Foma

umm i dont know what you mean by "printed charges".

Zed

[FOMA]

HI ZED.
With many thanks for Your scheme. I want to do the detector SD2000 on Your scheme. Can You have a good photo of the printed charges to do PSB.

[ZED]

Big differance

Aziz i have not gone any further than a 3000 and even there one sees a big differance between the 3000 and 2000.

Zed

[pulsfuehler]

One question about the schematics

Hello Zed, thank you for your explanation. Pulsfuehler

[Aziz]

Zed,

really good work. Thanks for the schematic. Try to get infos on newer ML detectors. I suppose, the newer models do not differ too much to older ones.

Aziz

[ZED]

G`day Pulsfuehler

The second crystal wasnt included because,well i just didnt think of it,m/lab included two crystals so as two detectors would be able to work in close proximity to each other with out interfering with each other to much.

One detector would use one crystal and the other detector would use the other crystal,both crystals on the board are diffirent,say 2.1 mhz and 2 mhz.
the crystals are enabled with jumpers and both crystals are not used at the same time on the one detector.

Thanks for your interest and your English is just fine.

Zed

[pulsfuehler]

One question about the schematics

Hello Zed, thanks for the schematics of the SD2000 but something doesn´t match when I compare the schematics and the pic belonging to this. In the pic I can find two crystals vertically aligned on the left upper half - in the schematic I couldn´t find the second crystal. Can you help me to solve this problem or doesn´t the pic belong to the schematic? Please apologize when you find some mistakes in my post but English is not my mother language. Best regards Pulsfuehler

Joke

Hi Zed,

Don't really expect the info on

the 4500. Bit of a Joke based on

someone asking for 4000. Which is

asking too much, after you have been

so generous on the 2000. Thank you again.

Not going to try and boot minelab.

As if anyone could get that information.

Minelab has figured out like others that new

models sell more detectors, and yes there are

improvements like the dual voltage which increases

the strength of some samples and should have been

done on the previous model. Oh well.


Hi Mrand,

The differential hook up, verses single ended, is probably

to reject things like 50 Hz or 60 Hz power line interference

and is also done on some VLF detectors as well. So probably

would not notice difference in performance until interference is

present.

[Mrand]

I am assigning myself the occurring question.
Are two tendencies for connecting by the front end circuit to receive coil.

First - receive coil is connected direct to (+) or (-) input front end OPAmp (met most often).

Other - receive coil is connected trough add differential OPAmp. This solution is meeting in the majority Minelab detectors and Fisher Impulse.

What deeper sense of this solution is?
Mrand