Universal PI Micro

[bugwhiskers]

UPIM Phote

The attached pic show the UPIM with both boards in place.

regards

bugwhiskers

[bugwhiskers]

UPIM 24 SAMPLER BOARD

The attached files are the schematic and pcb for the subject board. 24 samples isn't really enough but will have to do for the moment. If the results are encouraging in terms of discrimination it will provide the impetus for me to bite the bullet and get a SMD board professionly made. If the board were populated both sides there would be room for the chips for 128 samples. At 100 nS per sample (the fastest possible with a 20MHz CPU clock and 2 machine cycles per sample) digitizing the first 12.8 uS of the decay curve. Potential exists to perhaps take 64 samples of the early part of the decay and the other 64 evenly spaced further apart to take in the final stages of decay.

Over the next week I will be programming the beast.

regards
bugwhiskers

[bugwhiskers]

UPIM Coil/Pre-Amp Board

The attached files are the schematic, pcb and component overlay for the UPIM Coil/Pre-Amp daughter board.

The circuit is based on one of Carl's dual coil designs. The changes are the MOSFET's, they are now "P" channel and the second stage amp is an AD8055 to provide the grunt to charge/discharge the sampling caps quickly.

Interfacing a micro to a PI is far far easier with "P" channel devices because the back EMF and decay signal are centred about battery ground. The only down side to this is generally P channel devices don't have as high voltage ratings and the RDS is not quite as good as N channel devices.

The MOSFET included in this design was suggested by bbsailor, it has a 250V rating. The prototype has an IRF9640 (200 Volt), 0.5 ohm RDS and works fine.

Tomorrow I hope to have time to make and populate the 24 sample board and the small PCB that holds the push buttons.

regards
bugwhiskers

[bugwhiskers]

UPIM Motherboard

The attached files show pics of the UPIM Motherboard at work, Schematic and PCB.

The schematic has the legend for the bus, what each bus line does.

There are a few components mounted under the micro. The board is single sided with just a handfull of links and not too tight to make at home like I did using Kinsten pre-coated PCB material.
If anyone wants the CAD files (Eagle light) I will post these also.

In the pic you will see a PCB in socket #1, this is the coil/pre-amp board, it will be populated tomorrow and I will post the schematic and PCB file. It is based on Carl's Dual/Single coil with 2 stage pre-amp.

Today I ordered 3 of the micros but they won't arrive until the end of April so the final programming can't happen till then.

All the chips (10 * 16 pin PDIP's) required to take 64 samples won't fit on the PCB. I have laid out a SMD version but that is a while off being made. The compromise is to have a 24 sample version, using 3 of the 8 chips required to take 64 samples. The artwork is ready and I just have to make the PCB and populate it. All going well there will be a 24 sample PI up and running by the weekend, I for one can't wait to see how the samples in certain areas of the decay curve change with different metal types.

Don't be too shy to ask questions

regards
bugwhiskers

[bugwhiskers]

Following a suggestion by bbsailor the UPIM is now a Motherboard / daughter board system.

Over the next week I will be posting information and schematics for the 3 PCB's.

The Motherboard measures 3" * 3" (the reason for the small size will explained later). It holds the Micro (ATMEGA644 DIP 40 package), a programming header, a LCD screen header, MOSFET driver chip, minus battery *2 charge pump and conditioning circuitry to read the battery voltage and input push buttons.
The Motherboard has 2 bus sockets, socket 1 is for the coil drive and pre-amp circuitry and the second socket is for secondary signal conditioning, ie integrators or my switched multiple capacitor type.
The daughter boards measure 3" * 1.6" making the whole package very compact.

All micro source code to drive the display and daughter boards will be posted also.

At the moment I cannot source the micro so I am using an ATMEGA16 which has RAM limitations so the source code will change once the preferred micro is available.

The UPIM will not only make PI experimentation a lot easier but will provide an easy entry into the world of micro-control via the 3 essentials ie. input device (push buttons), micro-processor and output device (LCD graphic/text screen).

Stay tuned !

regards
bugwhiskers

[bugwhiskers]

Hi Stefan,

Thanks for your interest in the project.

I hear what you are saying, that aproach would be very easy but I am trying to keep the parts used to readily available and cheap. Some of the forum members live in areas where even common parts are difficult to obtain.

With regards to noise, integrators as used in most PI's are affected by noise, whether it be from the power rails or induced.

The 64 sample approach has a lot of noise immunity I believe due to the fact the gate to them is only open for a very short period and because they are disconnected when not being charged or digitised which again happens very quickly. The prototype is so noisy I can't have my workshop radio on and yet the jitter on the counts is only 1 or 2 and because there is so many of them to average the noise will be well and truly cancelled.



regards
bugwhiskers

[Stefan]

Power supply for BW's design

Hi Bugwiskers,

Been following your design with interest. I am using the Rabbit Core RCM4100 microprocessor as the basis of my PI design. The design is based on Candy’s patents so the sampling and pulse generation is somewhat complex. I was faced with the same problem you are having namely power supplies. Originally I decided to design and build my own power supplies using switch regulator chips. The problem with switch regulators is that high frequencies generated are feed back into the main battery supplies so carefull attention must be given to attenuating these signals.

However this was becoming time consuming so I looked at another means. I settled on commercially available DC/DC Converter modules made by TRACO Power. There is quite a range to choose from. The modules are fully shielded and have input filters for attenuation of the high frequencies. These modules are available from RS Components or Farnell but are somewhat expensive. If you consider the time spent on design, etc they are not that expensive and will save a lot on design.


Regards,

Stefan

[bugwhiskers]

Attachment ?

It really helps if I attach the file !

regards

bugwhiskers

[bugwhiskers]

Circuit for comments please.

The attached .PDF shows a circuit for generating the voltage required by the Opamps and Micro above the battery voltage.

Things to note, PIN 3 of IC14 is NOT at GND potential.
The switch needs to be a double pole double throw with center off.

The operating sequence is as follows.

The switch is in the middle position initially, everything off.
The operator momentarily moves the switch to the down position connecting the battery to C101 (~4700uF). This powers IC14. The pullup resistor R4 causes Pin 5 of IC14 to be LOW, this allows C66(~100uF) to charge via D1 and D3.
The operator then moves the switch to the up position. This connects the negative battery terminal to the micros Gnd and the battery positive pin to D4. C67 will now have approximately 2 times the battery volatge at its positive pin. IC1 will now be functional and provide power to the micro.
The micro's Pin 5 is a PWM output that will start sending pulses to the Opto OK1 and on to IC14.
The operator then moves the switch back to the down position for normal operation.
Most circuits use a 7660 chip or similar but the available current won't power the 11 chips downstream and the display. The only other alternative was to use a second battery but that would be awkward.

Any comments on the circuit would be appreciated.


regards
bugwhiskers

[Ray-NM]

Thanks for the info I will read thru it.
Raynm

[bugwhiskers]

Some source code for Ray-NM

Hi Ray,

Attached is a text file that is the source code for the program that is driving the LCD screen shown a few posts back. It's not fully commented but all the sub-routines have descriptive names like ss_bar = signal strength bar.

The commands within the LCD controller chip are too slow to execute so I have used a bit map approach. The micro holds in RAM an image of the screen. Clearing the image in RAM and setting pixels etc is performed much faster within the CPU. When the image is complete the whole lot is sent out to the LCD.

regards
bugwhiskers

[bugwhiskers]

do you have any code available for us to look at yet? My assembly language skills are quite rusty so I might have to look at it for a few months to understand how and what you are doing in the controller.
thanks
RayNM

Hi Ray,

All my work thus far has been in modular format. Hardware to do this and Software to do that. I am getting close to getting it all together.

One of the first things you should do is get a screen of some sort running off your micro to show internal variables etc... makes it much easier to debug your code.

I recently won two 240*128 LCD screens on ebay for $12US each (plus freight). Do an ebay search on LCD graphic display.
I have code for driving any graphic screen that uses a Toshiba T6963C chip
or the Hitachi HD44780 chip.
The code I have works but needs to be commented very well so people know what each part does.

regards

bugwhiskers

[bugwhiskers]

64 S&H OVERVIEW

The attached drawing shows the 64 sample and hold concept.

After the coil pulse is terminated the micro switches the output of the preamp to each of the 64 caps in turn. The user has control of the width of each sample the smallest being 50nS. Straight after the 4053 is toggled over and the stored charge on each of the caps is fed to the micro's AtoD, digitised and stored to the micro's RAM.

There will be 2 sets of samples in RAM, the current and an averaged set of previous samples. A user adjustable variable called "LAG" will control how often the current set will be averaged with the previous set. This will allow changes to be seen before they get swamped by the averaging.

With total control over coil pulse width, start of sampling time and the area of the decay curve to be sampled should allow the results to be analysed with a view to discrimination. Experiments with a prototype have shown the voltage on the caps to be very stable and relatively immune to the noise generated by the micro.

The top left box of the display will show the difference between the current sample and the averaged previous samples. If the user sees an area of difference then the right top screen can be adjusted to show a zoomed view (8 samples wide) of that area. The signal strength can be linked to that area also. I have seen graphs of decay curves of different metals and the area of the most difference is in the knee area of the curve.

More to come soon.

regards
bugwhiskers

[gef12]

like it

Hi BW
Yep it be looking good thus far , Waiting in anticipation

Gef fm OZ

[Ray-NM]

do you have any code available for us to look at yet? My assembly language skills are quite rusty so I might have to look at it for a few months to understand how and what you are doing in the controller.
thanks
RayNM