Universal PI Micro

[BJBJ]

Splendid project BW!

I have also done some designs around this type of detector, but since
i came across your thread i think i have try on this multi sample cell idea to.
I use a MSP430F1232 (low power).

I have some questions and ideas.

1: What is the purpose of AD8055?
If no additional gain are needed the 5534 can drive the sample cells
directly.1n over a range of 0 to 5V are not a heavy load for it!
You still have the slewrate of the 5534 anyway!

2:Why not remove the 4053 and simply switch the AD pin to three state
or just ignore read it during sample storage?

3:Instead of TC425 as charge pump driver (which are quite difficult to find)
an idea could be to use a HC14 with gates in parallel.

4: How many samples of the knee are actually needed?

5: What maximum coil charge rate are you going to use?

6: After your initial tests do you believe you need more then 10 bits (AD).

Reg
BJBJ

[bugwhiskers]

Hi BjBj,
Thanks for your interest in the project.
The AD8055 was initially chosen for it's slew rate and current drive in the previous bus arrangement. With the evaluation board as the micro platform a lot of things will change.
At the moment I am contemplating using no preamp at all, instead using the micro's on board programmable gain OP amp that is user S/W configurable for gains from 1-128. The advantage of this is the minimisation of noise and the fastest possible sample time with the advantage it brings for detecting small fast targets like small nuggets.
Amplification of any signal also involves amplification of noise. If instead of amplification the resolution of the AtoD (144dB) achieves the same objective without the noise and the extension of the earliest sampling time.

The TC424 was used because it allows a 5v micro output to switch the MOSFET at the full supply voltage ensuring full and fast switching.

The number of samples required is under review.
The coil charge time is dependant on the coil used and can be made automatically detectable (see previous post) and user adjustable.

Re the number of bits required, as stated above, the more bits the more "gain".
Another change is the use of a 2 coil arrangement, either double "D" or seperate RX TX so the RX signal is the correct polarity for the AtoD. This arrangement will also allow either "P" or "N" channel MOSFET's to be used.
Regarding the 4053, it isn't required in the new arrangement.

regards
bugwhiskers

[Unregistered]

Hmm, i really wonder if a internal CMOS OP amp will give you any
advantages over the bipolar 5534?

Which micro have you finally settled for?
ADUC845?

The resolution of 144db cant easily be realised, the 4051 will swamp
it out, Rds of the switches shift due to temp and voltage variations.

I recall sigma-delta AD quite, aduc 845, 1.37kSPS!!
Carl said in some papers that there whas this 3khz pulse rate but
one should do with far less i suppose?

[BJBJ]

The idea with DD coils are going to be interesting indeed!
Perhaps one could use sailors mini coil arrangement!

But on the other hand the buffer+PGA seams to be quite silent,
noise in uV region.

[bugwhiskers]

Hmm, i really wonder if a internal CMOS OP amp will give you any
advantages over the bipolar 5534?

Which micro have you finally settled for?
ADUC845?

The resolution of 144db cant easily be realised, the 4051 will swamp
it out, Rds of the switches shift due to temp and voltage variations.

I recall sigma-delta AD quite, aduc 845, 1.37kSPS!!
Carl said in some papers that there whas this 3khz pulse rate but
one should do with far less i suppose?

Hi unregistered,

The RDS of the analogue switches is actually beneficial in conjunction with the caps in filtering out some noise and changes due to temperature will be miniscule.
The 1.37ksps is the maximum rate of the ADUC845. In an earlier post I did mention that the full 24bits may not be achievable.
I want to try just the internal OP-AMP firstly as it will make for less hardware and if need be I can always go back to an external OP-AMP.
The problem with "on the fly projects" is that there will always be changes of direction in persuit of excellence.

regards
bugwhiskers

[bugwhiskers]

Hi BjBj,

Any of bbsailors dual coils should work very well. A coaxial coplanar is another possibility.

The AtoD reference of 2.5 volts, divided by 24 bits (16.8 million) is 0.149 microvolts, just as well the PGA is quiet eh ?


regards
bugwhiskers

[BJBJ]

Unregistered was just me again! I wonder why it went unregistered?

Anyhow,yes it will act as a simple Rc filter but the voltage in and out
are depending on the voltage in and out, the less voltage into the switch
the worser the accuracy.To remedy that a bit one can drive the Mux from
either +10V or +/-5volt or simply switch to a better Mux.

Indeed, there are always a bit of laboratoring with new designs.

Your doing great.Keep up the good work.

Regards
BJBJ

[1843]

Hi bugwhiskers,
Which program do you use to write your project (u-controller data)?
Regards

[bugwhiskers]

Hi 1843,

There is a link back in post #104 that shows the software suite or IDE for programming.

regards
bugwhiskers

[nitrous]

will you have an SMT system available?

Hi there Bugwhiskers

Great project you've developed. Especially since so many others have become involved.
I wonder if you'll have a miniture version of your PI system available.

I would like to make a very small version, perhaps modified with a separate LCD/Audio module. What will the final size be and will you be making SMT versions available? Something that has the main board in the headphones? An other possibility would be to use this board for a pinpointer with appropriate coil design. Again, a small form factor would be very helpful.

Thanks,
Doug

[bugwhiskers]

Hi nitrous,

Thanks for your interest in the project.

There are no plans to make a miniature version of the evaluation board at this stage.

regards
bugwhiskers

[nitrous]

thanks guy

how big is the board expected to be at this point?
The 'here and now' is at least as interesting as the hereafter!
Who knows what the future might bring.
Thanks for the reply.
Doug

[bugwhiskers]

Hi nitrous,

The 2 evaluation boards that I ordered a few weeks ago just turned up 10 minutes ago. They are 4 inches by 5 inches and have not been designed to be as small as possible. However, they are well made and cheap and an easy way for users to get into micro controlling their PI experiments. There is also a 4 inch * 1.5 inch prototype area.

The kit came with 2 power plug packs, neither are suitable for Australia but there is provision for using a 9v battery which allow me to get it up and running straight away. The documentation includes a BOM which I couldn't obtain from the Internet.

regards
bugwhiskers

[bugwhiskers]

A quick note for BjBj

Hi BjBj,

The resistors show in the schematic that are on the inputs to the AtoD are zero ohms. The caps are 10nF which is what I am using in the bus prototype.

The screen should be up and running by the weekend, a bit slower than anticipated due to paying work commitments and getting used to a different micro's instruction set.

Regarding a better MUX, Maxim make a MAX4051, the specs of which are slightly better but at quite a price premium.

regards
bugwhisker

[Unregistered]

Hi BjBj,

The resistors show in the schematic that are on the inputs to the AtoD are zero ohms. The caps are 10nF which is what I am using in the bus prototype.

The screen should be up and running by the weekend, a bit slower than anticipated due to paying work commitments and getting used to a different micro's instruction set.

Regarding a better MUX, Maxim make a MAX4051, the specs of which are slightly better but at quite a price premium.

regards
bugwhisker

I was more into the DG range of muxes, however as they are really premium they come with a premium price to, but before switching to premium muxes
it would indeed be interesting to hear what your results show with the Aduc
device.

Regards
BJBJ