Preamp

[Teleno]

Two boards, one for TX one for RX better noie isolation that way, to PLENTY of filtering on the Rx board.

Teleno, Express looks just fine. I didn't want to have to use another package, have you also tried DIPTRACE? http://diptrace.com/

Great 3D with it too. Limited yes, but it we do this as two boards then I can still do this as I have the full version. there is also a LINUX version - WOOT!!

Great find! Diptrace for Linux has no time limit and 300 pins is more than enough or the project.

Regarding the board question, noise is not caused by the Tx circuit. Do not mistake the flyback transient with noise. The transient is well handled by the Rx circuit, no need to separate boards.

[eclipse]

Is the STP11NM80 transistor selected for a purpose? (I.e perhaps it has the spice model built in), there are better trans if this is not the case.

[Teleno]

Is the STP11NM80 transistor selected for a purpose? (I.e perhaps it has the spice model built in), there are better trans if this is not the case.

Nope just because it's convenient for the sim. I've selected the IRFIBF30 which has a breakdown of 1,000V and Co < 300 pF above 25 Vds. Ron is about 4 ohm or a max current of 3 A at 12 V.

[WM6]

Great find! Diptrace for Linux has no time limit and 300 pins is more than enough or the project.

.

You can get 500pin/2 layer, free, by asking (registering to) editor per email. Not truly Linux, it can run under Wine.

[green]

Some questions that might be important for component selection and board layout for coil driver and preamp. Works with mono coil, IB coil or either? Peak coil current? Fast diode between Mosfet and coil? Snubber? EF cancel by two sample difference or bipolar pulsing(needs bipolar preamp)? Probably more.

[Teleno]

Some questions that might be important for component selection and board layout for coil driver and preamp. Works with mono coil, IB coil or either? Peak coil current? Fast diode between Mosfet and coil? Snubber? EF cancel by two sample difference or bipolar pulsing(needs bipolar preamp)? Probably more.

Well, if you looked at my design you'll see it's monocoil, monopolar and no snubbing.

Since the purpose is to improve speed and signal/noise relative to Surfmaster and similar, I'm concentrating on the (pre)amplifier and keeping it simple. Further refinements can be considered once the concept is proven.

By the way, all further signal processing (GB, EF etc.) will be carried out by an MCU.

[6666]

TELENO

You said in a previous post in this thread that

I have posted my novel GB scheme in another thread, should be tested in Aussie goldfields.

If I search on your name 22 threads show up, I have looked in most of them, but so far I have failed to find any GB schematic
could you please give me a glue where to find this GB information , thanks.

[Teleno]

TELENO

You said in a previous post in this thread that

If I search on your name 22 threads show up, I have looked in most of them, but so far I have failed to find any GB schematic
could you please give me a glue where to find this GB information , thanks.

I never said there was a schematic. I've disclosed a method. Anyone can implement it as a circuit or in software, according to preference.

This is the method: http://www.geotech1.com/forums/showt...mit-time/page3

[6666]

I never said there was a schematic. I've disclosed a method. Anyone can implement it as a circuit or in software, according to preference.

This is the method: http://www.geotech1.com/forums/showt...mit-time/page3

Thanks for finding the correct thread, unfortunately mathematical formulas are not my forte, looking at Q's description your idea seems to be to have 2 transmit pulses of different length and 2 samples for each transmit pulse is that correct ? is the sampling done with a single intergrater.

[green]

http://www.geotech1.com/forums/showt...875#post207875

Trying to learn something about using an adc. Searched to find the sample resolution needed for a PI detector. Five micro volts was mentioned as probably not being enough in the above thread. What would be a good resolution to try for?

[Teleno]

http://www.geotech1.com/forums/showt...875#post207875

Trying to learn something about using an adc. Searched to find the sample resolution needed for a PI detector. Five micro volts was mentioned as probably not being enough in the above thread. What would be a good resolution to try for?

The resolution is given by the noise level. If your output noise is 2mV then 11 bits is more than enough (with a 5V reference it resolves 2.4mV). You go for a standard 12-bit ADC and scrap the least significant bit.

[Old cart]

http://www.geotech1.com/forums/showt...875#post207875

Trying to learn something about using an adc. Searched to find the sample resolution needed for a PI detector. Five micro volts was mentioned as probably not being enough in the above thread. What would be a good resolution to try for?

In addition a to d resolution it is very important to consider the system noise level. For example if the system has 5 mV P-P noise it does little good to have 5 uV of resolution. Note also that few a-d converters sample fast enough to be able to take multiple samples during a typical 10 uS sample window. This may mean you will have only one sample taken in that period. Worse, if you can not control precisely in time WHERE that sample is take it wil be difficult to make any sense of it at all.
While it is possible to sample the whole receive, and even transmit, waveforms of a PI it seems it would be very expensive to do this with enough time and amplitude resolution to be of great value. Probably better to sample after the integrator with a slow 16 bit converter. This eliminates timing problems and also noise is lower there.

[green]

In addition a to d resolution it is very important to consider the system noise level. For example if the system has 5 mV P-P noise it does little good to have 5 uV of resolution. Note also that few a-d converters sample fast enough to be able to take multiple samples during a typical 10 uS sample window. This may mean you will have only one sample taken in that period. Worse, if you can not control precisely in time WHERE that sample is take it wil be difficult to make any sense of it at all.
While it is possible to sample the whole receive, and even transmit, waveforms of a PI it seems it would be very expensive to do this with enough time and amplitude resolution to be of great value. Probably better to sample after the integrator with a slow 16 bit converter. This eliminates timing problems and also noise is lower there.

What does system noise mean without knowing system gain? If system gain is 10000, system noise 5 mv p-p. Noise is .5 uv p-p at input. The target defines resolution and noise level. Detecting a US nickel at 15 inches with a 8 inch diameter coil with 1 amp peak current requires 1 uv resolution referenced to input(coil volts). Higher peak current or a larger diameter coil could reduce required resolution.

[Old cart]

What does system noise mean without knowing system gain? If system gain is 10000, system noise 5 mv p-p. Noise is .5 uv p-p at input. The target defines resolution and noise level. Detecting a US nickel at 15 inches with a 8 inch diameter coil with 1 amp peak current requires 1 uv resolution referenced to input(coil volts). Higher peak current or a larger diameter coil could reduce required resolution.

That is absolutely correct. The resolution you require is really a ratio of the largest signal to the smallest, AT THE PLACE YOU INTEND TO DO THE DIGITIZING. This can be measured using the techniques described in the preamp thread.
If you for example want to acquire all of the data out of a preamp that has +/-5 volt supplies and a measured noise level of say 500uV then you would need 10V/500uV or a 20000 to 1 ratio. Each bit of an a to d converter can describe a 2 to to1 ratio. This means a 15 bit a to d would be required because it has 2^15 (32768 descrete digitizing levels. You should always have at least 1 bit more ( double the resolution) than you need due to the +/- 1 bit uncertainty inherent in all digital processes. All this assumes theoretical ideal processes, no signal averaging or other processing, and that you want to digitize the whole signal which you may not. In the case that you are willing to ignore the larger parts of the signal you just reduce the max signal to that you really want to see. For example if the signal is clipped by diodes at +/-.7v. This would reduce the resolution requirements by a factor of 7 or roughly 3 bits. One caution, if you put more that the rated signal into an a to d it is likely to misbehave or even be destroyed. It is up to the user to determine what those behaviors are limits are...
Of course signal processing after the a to d can dramatically alter the effective resolution. For example, if you average the samples 8 times you effectively add 3 bits of resolution (2^3) AND you reduce the noise by a factor of the square root of 8. This assumes the noise is not synchronized with the sampling (is asynchronous). There are other processes you can use lie boxcar integration and digital filtering, even adaptive filtering, and correlation that can bring the signal out of the noise. These can get quite complicated but a quick Google search will yield a lot of data.

Digital sampling and filtering hold great promise to improve the performance of the detector. MAYBE WE SHOULD ADD ANOTHER SUB TOPIC TO THIS THREAD TO MOVE THIS DISCUSSION TO.

[green]

That is absolutely correct. The resolution you require is really a ratio of the largest signal to the smallest, AT THE PLACE YOU INTEND TO DO THE DIGITIZING. This can be measured using the techniques described in the preamp thread.
If you for example want to acquire all of the data out of a preamp that has +/-5 volt supplies and a measured noise level of say 500uV then you would need 10V/500uV or a 20000 to 1 ratio. Each bit of an a to d converter can describe a 2 to to1 ratio. This means a 15 bit a to d would be required because it has 2^15 (32768 descrete digitizing levels. You should always have at least 1 bit more ( double the resolution) than you need due to the +/- 1 bit uncertainty inherent in all digital processes. All this assumes theoretical ideal processes, no signal averaging or other processing, and that you want to digitize the whole signal which you may not. In the case that you are willing to ignore the larger parts of the signal you just reduce the max signal to that you really want to see. For example if the signal is clipped by diodes at +/-.7v. This would reduce the resolution requirements by a factor of 7 or roughly 3 bits. One caution, if you put more that the rated signal into an a to d it is likely to misbehave or even be destroyed. It is up to the user to determine what those behaviors are limits are...
Of course signal processing after the a to d can dramatically alter the effective resolution. For example, if you average the samples 8 times you effectively add 3 bits of resolution (2^3) AND you reduce the noise by a factor of the square root of 8. This assumes the noise is not synchronized with the sampling (is asynchronous). There are other processes you can use lie boxcar integration and digital filtering, even adaptive filtering, and correlation that can bring the signal out of the noise. These can get quite complicated but a quick Google search will yield a lot of data.

Digital sampling and filtering hold great promise to improve the performance of the detector. MAYBE WE SHOULD ADD ANOTHER SUB TOPIC TO THIS THREAD TO MOVE THIS DISCUSSION TO.

[If you for example want to acquire all of the data out of a preamp that has +/-5 volt supplies and a measured noise level of say 500uV then you would need 10V/500uV or a 20000 to 1 ratio.] I'm still missing why you give a noise level without referencing it to the input or include a gain. A preamp with a gain of 10 or 1000 would make a difference finding the nickel at 15 inches with a 15 bit a to d converter. The noise after filtering should to be referenced to a frequency band that includes the target signal. Analog or digital filtering. Some low noise op amps include a 10 second .1 to 10 Hz scope trace in there spec sheet. I'm thinking the target signal is less than 10 Hz so something similar would make sense, maybe not.