LOOKING FOR GOLDSCAN 4 Schematic.

[Geo]

Reg, i am aware of this thread relating to GS4, just was not sure about the reference to the GS5/TDI. Thought i missed something previous in the posts and GS5 got me interested.

I have not seen a Circuit layout of the GS5 and was just asking what the differences were.

All good

Sid

Sido, here is the schematic of GS 5. I found it here at Geotech and i am not sure if it is 100% OK.

[Geo]

[ATTACH]22403[/ATTACH] you're absolutely right gs4 can have two tones as tdi !

Orbit this is my TDI at my Lab!!!!!

[Geo]

Geo,

Do you have the original TDI, the later TDI or the TDI Pro?

The TDI pro has two basic changes when compared to the TDI and those changes are the values of 4 capacitors (on the original 200 units) or 2 capacitors (on later units) and moving the internal volume control to the outside. At one time, White's indicated they might provide instructions on how to make the conversion. I am not sure if they ever did that. Maybe Carl will jump in and answer that question.

The changes were made to help with small gold detection and a little less noise from the audio amp.

As for changes, I am very hesitant to offer suggestions that require changing surface mount parts.

Reg

Reg, i have the original. It is the version with the microprocessor for timing.
I added a potentiometer for audio volume and another one for fine GB adjusting as the Pro model.
I am interesting to reject objects with size 2x2x2 cm when i search with the 1x1m coil. If there are 3..4 objects with these dimentions then i have problem. If i will keep the coil 40 cm up of the ground it is OK but i lose depth.

Regards

[Orbit]

you're absolutely right gs4 can have two tones as tdi !

[Reg]

Any GS 5 owners out there reading this thread? If so, interested in adding the single tone mod to your detector? This allows you to select either high conductor or low conductor only or both. BTW, this can be done to the GS4 also.

Reg

[sido]

Reg, i am aware of this thread relating to GS4, just was not sure about the reference to the GS5/TDI. Thought i missed something previous in the posts and GS5 got me interested.

I have not seen a Circuit layout of the GS5 and was just asking what the differences were.

All good

Sid

[Reg]

sido,

Sorry about the confusion. You asked about similarities between the GS 4 and the TDI but I misread your question.

This thread is about the GS 4 which was made in the lat 80's and 90's I believe. The Goldscan 5 (GS 5) was built much later, 2005 maybe. Are there any similarities between the GS 4 and the TDI? Yes, some of the fundamental concepts are the same but a lot of the circuitry was changed including the audio. On the GS 4, the audio is a tick tick variable frequency audio, while the GS 5 or TDI has an audio in which the audio level increases as well as a small tone change.

The GS 5 has two channels of information like the GS 4 used for ground balance.

So, there are both differences and similarities. Get to where you fully understand the GS 4 and you will have a pretty good idea of how the TDI or the GS 5 works.

Reg

[Reg]

Geo,

Do you have the original TDI, the later TDI or the TDI Pro?

The TDI pro has two basic changes when compared to the TDI and those changes are the values of 4 capacitors (on the original 200 units) or 2 capacitors (on later units) and moving the internal volume control to the outside. At one time, White's indicated they might provide instructions on how to make the conversion. I am not sure if they ever did that. Maybe Carl will jump in and answer that question.

The changes were made to help with small gold detection and a little less noise from the audio amp.

As for changes, I am very hesitant to offer suggestions that require changing surface mount parts.

Reg

[sido]

Goldscan 5?? I believe the circuit above is the goldscan 4.

What are the differences between the two?

Sid

[Reg]

sido,

The first 200 TDI's were extremely similar to the Goldscan 5 in layout. The later units, the ones with GB ON REQUIRED above the Conductivity switch are different. These later units use a microprocessor to set the timing, thus there is no internal adjustment that can be tweaked to shorten the delay.

White's purchased the rights to the GS 5 and that became the basis for the TDI. That is why there is such a similarity.

Reg

[sido]

Hi Reg, following the above post with interest,

Is the TDI similar in circuit layout to the Goldscan IV??

I keep seeing the above referred to the TDI??

Cheers Sid

[Geo]

Ohhh Reg!!!!
So much effort for nothing.
I have not a GS 4. I attached the address because you did not known where was the thread of Eric.
But if you have any Tips for TDI are welcome

My wishes

[Reg]

Geo,

I use different IC's in place of the NE5534 than those mentioned in your link. I have used the AD797 successfully but you have to place diodes across the feedback resistor to limit the IC from going into saturation. It will work fine that way. However, there are a few ICs' that are almost as good or even better.

The LME49990 has lower noise specs and works without any problems. The OPA211 works well and is almost as low noise specs plus the current draw is much lower. The OPA 228 works fine also but is not quite as fast as the LME and the 211. All three are precision opamps having very low offset. This eliminates the need for any offset compensation.

The LME49990 and the OPA211 do not come in the dip package so an adapter is required. The OPA228 does come in the dip package so it can be used directly. In fact, I recently modified a Goldquest by replacing the 5534 with the OPA228. The detector was having drift problems and this eliminated that issue.

Now, as mentioned, one advantage of these three IC's is the fact no offset adjustment is required. So, the preamp circuitry becomes simpler because no compensation is required either This does away with several parts and basically leaves the opamp, feedback and input resistor as the key parts left except for the PS leads and they should be changed also. THE 47 ohm resistors in series with the power supply leads can be removed. Just use a tantalum cap on each lead and parallel the tantalum with a .1uf to take better care of the higher frequencies.

BTW, if you read Eric Foster's posts you will see where he dropped the input resistor to the preamp from 2.2k to 1K to reduce noise on his later designs.

One thing I didn't mention is the GS 4 has a limit on the current it can produce for the 5V supply. So, one has to be careful when selecting parts to substitute. I found this out the hard way, when I suggested the OPA4277 as a replacement for the quad opamps used in the GS 4. Well, a guy ordered the OPA4227, which is also a quad opamp. The difference is the 4227 draws about 4 times as much as the opa4277. So, the 4227 draws about 16ma each chip and with two of them, the 32 ma was too much for the designed power supply when combined with all the other circuitry drawing current from the 5V supply. Thus the 5V supply was loading down. That took a while to figure out.

One final issue you might check and that is the GS 4 I have would have a hum in headphones because of the pulse rate of the detector. To eliminate this problem I raised the pulse rate to over twice the original. This eliminated the buzz and still worked well. If you decide to do this, remember that simply raising the pulse rate by changing the timing cap on the 555 will also shorten the pulse length.

Reg

[lucafa]

Hi all.

I'm happy that these posts are appreciated.

Before continuing the discussion I mean to follow the instructions of reg set to zero volts in the calibration points.
This is to avoid confusion.
I summarize here the calibration sequence:
I remind you that switch SW1 has the following function 1=OFF (first position is at the top, look at the arrow), 2=ALL, 3=SEL1, 4=SEL2.

RV1= switch SW1 to ALL, pot GND minimum side R52 , press and hold RESET button, adjust RV1 for zero volts on pin 7 U12B.

RV3= switch SW1 to ALL, pot GND minimum side R52 , press and hold RESET button, adjust RV3 for zero volts on pin 14 U12D.

RV5= switch SW1 to ALL, pot GND minimum side R52 , press and hold RESET button, adjust RV5 for zero volts on pin 7 U13B.

RV7= switch SW1 to ALL, pot GND minimum side R52 , press RESET button and hold, pot SENS maximum, adjust RV7 to have zero volts on pin 14 U13D. Check if it remains zero volts on U13D varying the pot SENS.

RV6= switch SW1 to OFF, pot GND minimum side R52 , press RESET button and hold, pot SENS maximum, adjust RV6 to have zero volts on pin 14 U13D. Check if it remains zero volts on U13D varying the pot SENS

RV2= use oscilloscope channel 1 probe to the gate Q4, trigger channel 1, channel 2 probe to the gate Q8, pot DELAY (or FOIL REJECT) at minimum, adjust RV2 for a delay of approximately 17uS (values of my MD), vary pot DELAY to the maximum and read delay about 95uS.

RV8= use oscilloscope channel 1, show at least two pulses, put gnd trace oscilloscope and place on a line screen (zero), back in DC, adjust RV8 to keep track of a two pulse and the other on the line of previous gnd.

RV4= from various posts and forum how to do is this: to adjust a value that ranges from -4 to -15 mV, find the point at which snaps pin 8 of U12C from -4.3 V to +4.3 V with micrometric movements and MD for an answer without disturbance without an object, the audio signal with the subject at a good distance.
(And this thing that you are 'talking in these posts, at least I do )

[Geo]

Lucafa,


Did you know that the simple NE5534 used as the preamp can cause problems? Yes, there are differences in the amplifiers depending upon the manufacturers and some work better than others. Some are simply not as fast as others among other things.

To find out, you have to test the opamps using a technique mentioned by Eric Foster quite some time back on this forum. Right now I can't tell you where that information is but it should be there.

Reg

Here eric speak about op.amp for front end...

http://www.geotech1.com/forums/showthread.php?11040-Low-Noise-Front-End-for-P-I&highlight=