GOLDSCAN 5 SCHEMATIC QUESTION

[dbanner]

Which micro do you plan on using, will it be a PIC?

[eclipse]

I'm doing the timings with microcontroller, I may offer pieces for sale in future. It reduces complexity alot.

[dbanner]

As i know TDI and TDI pro have the same schematic.
So the timing schematic is wrong. TDI don't use 4538 for timing but a uc (ATINY).
However i want to believe that the times of GS5 and TDI are the same.

Just out of curiosity, can't someone scope out the timings of the two for comparison? This would be informative? Here i post nice schem of front end GS5.

[Altra]

As i know TDI and TDI pro have the same schematic.
So the timing schematic is wrong. TDI don't use 4538 for timing but a uc (ATINY).
However i want to believe that the times of GS5 and TDI are the same.

Hi Geo,

The first TDI's used 4538's, and later switched to a microcontroller. Some where on one of the forums Reg or Carl mention that there was a first run of TDI's with through hole components and not smd. I recall it was less than a 100 units.

Here is a photo of a proto type just like the one I have

[Geo]

Check out the first page, it has the timings setup, i guess you need scope to do this?

As i know TDI and TDI pro have the same schematic.
So the timing schematic is wrong. TDI don't use 4538 for timing but a uc (ATINY).
However i want to believe that the times of GS5 and TDI are the same.

[dbanner]

Hi,
Looking at this schematic : it is made for a 2 coils detector. The MOS in this part are small current devices, and their gate control needs additional circuitry.
And , LM394 is very good matched pair , but it is now not available . (May be THAT300 is a good remplacement.)
I think there is easier way to improve the front end of the GS5. Was it the goal while asking this question?

I was looking at possible modifications to GS5. But I like the sd2000 audio circuit. LM394 is no problem. Suitable replacement can be found.

[dbanner]

does anyone know the setting up for the GS 5 ??

Check out the first page, it has the timings setup, i guess you need scope to do this?

[Idefix]

By the way, is the sd200 schematic(the front end) accurate?

Hi,
Looking at this schematic : it is made for a 2 coils detector. The MOS in this part are small current devices, and their gate control needs additional circuitry.
And , LM394 is very good matched pair , but it is now not available . (May be THAT300 is a good remplacement.)
I think there is easier way to improve the front end of the GS5. Was it the goal while asking this question?

[daverave]

does anyone know the setting up for the GS 5 ??

[dbanner]

By the way, is the sd200 schematic(the front end) accurate?

[dbanner]

By "Matching" we mean value matching. A typical capacitor may be rated at +/-5% of marked value. Now we take a bag of 100 and measure the capacitance of each. It is probable that some capacitors from the bag could be as much as 10% apart in value. Say we test a batch of 470nf. +5% would be 493.5nf, -5% would be 446.5nf these two have a 47nf difference. For our differential integrators to balance the RC time constants need to be equal between the inputs and channels. So out of the bag we want to pick 4 capacitors that are within say 1% or less of equal value and we use 1% tolerance resistors. Most hobby builders can get away with broader tolerances. But if you are building a 100 detectors on an assembly line and want the ground balance or disc control to react the same for each unit consistently you need to use "matched" components. In metal detectors, differential integrators and dual channel differentiators are circuits to be matched.

Yes, i understand "matching pairs", but can you show me single cap integrator example on sd2000 schematic?

[Geo]

Hi Geo, Have you had oportunity to take some more pictures?

Not now. Maybe after 10...15 dayw if will remember me again.

[Geo]

Here is a preamp which would feed single cap integrators from one of my builds. Change the AD8055 to 1/2 NE5532 and it may be what Geo's TDI preamp configuration looks like? Some good photos would tell.

It seems good. Connect a resistance between positiveinput of U2a and earth.

[Altra]

i think i see matching caps at integrators on sd2000schematic? can you expand a bit on your explanation please.

By "Matching" we mean value matching. A typical capacitor may be rated at +/-5% of marked value. Now we take a bag of 100 and measure the capacitance of each. It is probable that some capacitors from the bag could be as much as 10% apart in value. Say we test a batch of 470nf. +5% would be 493.5nf, -5% would be 446.5nf these two have a 47nf difference. For our differential integrators to balance the RC time constants need to be equal between the inputs and channels. So out of the bag we want to pick 4 capacitors that are within say 1% or less of equal value and we use 1% tolerance resistors. Most hobby builders can get away with broader tolerances. But if you are building a 100 detectors on an assembly line and want the ground balance or disc control to react the same for each unit consistently you need to use "matched" components. In metal detectors, differential integrators and dual channel differentiators are circuits to be matched.

[dbanner]

No, I think they may have changed to single capacitor integrators. See the SD2000 schematic. Differential integrators need matched caps and resistors, so it's easier to mass produce a detector using single cap integrators.

i think i see matching caps at integrators on sd2000schematic? can you expand a bit on your explanation please.