Universal PI Micro

[bugwhiskers]

Hi Alexismex,

The ground will most certainly change the response but one thing in our favour is that Iron & Lead are quite different in conductivity from desireable targets like Gold and Silver and Copper. Metals with conductivity greater than the set "pivot point" will get through.
I am doing a lot more "paying" work now so my R&D time is somewhat limited.

regards
bugwhiskers

[bugwhiskers]

Error in schematic

There is a problem with the schematic posted earlier. It shows the output from IC3 being subtracted from the output of IC4C which won't work as the IC4C signal is very small at the threshold of detection.
The ground signal has to be subtracted from IC4A&B simultaneously.

Will post the revision when done.

regards
bugwhiskers

[bugwhiskers]

Revised schematic

Attached is a .PDF showing the revised schematic of the discrimination circuit.
The fix is very elegant in that the additional OP amp is now not required.
The ground balance signal will also take care of any pre-amp offset automatically but not the signal strength signal for the audio, this can be done in software or by isolating with a cap by those who want to implement a purely analogue circuit.

regards
bugwhiskers

[bugwhiskers]

Yet another fix.

Attached is another revision that has been tested in SPICE and works. The previous schematic wouldn't subtract the ground signal equally, this one does.
V1 is the ground sample, V3 the first sample and V2 the second sample. To save the extra OP amp U2 & U3 go straight to the comparator. U6 just buffers sample 1 after it is halved by the resistive divider R14/R15.
If the output of U2 goes above U3 then the output of the comparator U4 goes high to signal a desireable target to the micro. The circuit isn't complete but has just enough components to test the method.
By having all the Op amps in one quad package it is hoped that temperature drift will be minimised.

regards
bugwhiskers

[Unregistered]

Hi asguard,

I have just emailed you all the files, I even sent you the source code. However, as stated before, they are "as is" and I cannot support either the hardware or software as I have moved on to the evaluation board. Please don't contact me and ask for help with any aspect of it either in private or public. After posting my private messages in public I guess you won't be expecting too many favours from me again.

regards
bugwhiskers

Amazing what it took to actually get you to do what you said you would. Thanks, have just checked email(theres one there from you) have not yet opened. Had I have not posted here, somehow, I think you would not have bothered even replying.

Didn`t ask for support, as it seems you were using it as an excuse. Defend it how you will I`m sure you`re not short of supporters. Never criticized what you`re attempting, seems like there was something similar explained from memory in the archives somewhere on this forum.

WireChief you`re abit of a flintstone character aren`t you, if you call truth dumping on ones self well... I guess you`ll always smell clean

Didn`t bother logging on this time, some timeout/posting probs so kept it short, I got a couple of funny Bugwhiskers pics you`ll find amusing, they`re right on topic, should brighten your day up. post shortly

Asguard

[Wirechief]

Amazing what it took to actually get you to do what you said you would. Thanks, have just checked email(theres one there from you) have not yet opened. Had I have not posted here, somehow, I think you would not have bothered even replying.

Didn`t ask for support, as it seems you were using it as an excuse. Defend it how you will I`m sure you`re not short of supporters. Never criticized what you`re attempting, seems like there was something similar explained from memory in the archives somewhere on this forum.

WireChief you`re abit of a flintstone character aren`t you, if you call truth dumping on ones self well... I guess you`ll always smell clean

Didn`t bother logging on this time, some timeout/posting probs so kept it short, I got a couple of funny Bugwhiskers pics you`ll find amusing, they`re right on topic, should brighten your day up. post shortly

Asguard

Yep I even have the gut like ole Fred haha !

John Tomlinson,CET
John's Detectors

[rWAVE]

Greetings bugwhiskers,

I am really enjoying the development process you are going through (hope you are too) and look forward to new discoveries unearthed by your efforts. As inspiration is NOT gained from some recent, Unregistered posts, the following "urban legend" seems more appropriate:

One story goes that "Thomas Edison failed more than 1,000 times when trying to create the light bulb". (The story is often told as 5,000 or 10,000 times, depending on the version). When asked about it, Edison allegedly said, "I have not failed 1,000 times. I have successfully discovered 1,000 ways to NOT make a light bulb".

As my only MD experience is with an ACE 250, I am not familiar with the setup and calibration of a PI detector, prior to "swinging". Based on your design, could you briefly mention the process needed for your design? For example, when you arrive at your hunt area, you turn the detector on and then . . . ?

Your posting of the discriminator board schematic on 07/03/07, you state that R22 is used for a no-target zero adjust. Is this an adjustment required regularly, thus needing front panel control or is it part of a final calibration once the complete unit has been built? Since this is a uC-based project, it seems that after proof-of-concept prototyping is done, R22 could be replaced with a uC-controlled digital pot for auto-zeroing.

I wish you continued success on this project.

Regards.
Richard

[bugwhiskers]

Hi Richard,

Thanks for your interest in the project. The adjustment pot is now gone. It's purpose was to create a null with no target present, it can also be achieved in software by micro adjustment of the position of the second sample.

Later today I will be posting the revised schematic which is the whole circuit.

The new circuit uses a rotary encoder (digital pot) for making adjustments like setting the null for various coils.


regards
bugwhiskers

[bugwhiskers]

Getting close.

Attached is the current schematic and pcb .PDF's.
By using a "P" channel MOSFET the back EMF can be used to create the -5V required by the OP amps.The components to the right of IC2 (79L05) are used to achieve this saving a lot of software overhead and also reducing noise.

The next step is making and populating the board and finalising the software.

regards
bugwhiskers

[bugwhiskers]

Attached is a colour .PDF of the PCB to make it a little clearer.
Since the earlier post I have added circuitry to condition the battery voltage for reading by a spare AtoD and also added more de-coupling caps.
Added a protection diode for the main AtoD in case it's input goes negative, the back EMF catcher zener polarity error has been fixed also.
There are about 17 jumper links (reddish lines) which is unavoidable in such a compact single sided board.
Added some test points for attaching the CRO probe as well.

regards
bugwhiskers

[Ray-NM]

bugwhiskers
You have been very quiet lately.
did it work so well that now you are out finding gold and coins?
RayNM

[bugwhiskers]

Hi Ray-NM,

I lashed up the circuit posted earlier and the low frequency noise (0-10Hz) was horrendous. This necessitated a major rethink and a chip recommended by Dave Emery, the AD797. It's low frequency noise is very low.
The other changes are the MOSFET is now an IRF740 with a pair of transistors doing the voltage translation so the mosfet driver can be driven by the micro. The noise is now much lower and I am working on making the pre-amp a multistage filter otherwise the sample caps will have lots of EMI noise on them (prevention is better than cure).
It's a long slow process but then again if it was easy the top of the range detectors wouldn't cost so much.

regards
bugwhiskers

[BillA]

"if it was easy the top of the range detectors wouldn't cost so much"
lol
ah BW, those are not the words many (most ?) will want to hear
the goal is to knock out all iron with a $550 detector
as an engr I am quite comfortable with high performance = high price,
not a deterrant at all if the performance is there

do keep at it, your stds seem appropriate
BR, BillA

[Alexismex]

HELLO BW,
Good work , I enjoy you take the IRF740 , to me it is the best , I experiment a lot with all kind of Mosfet and exotic Mosfet and because I live in a lucky place(in Mexico) near the big Papa USA and I have a cool access to Mouser , Newark, Digikey etc... to check components...
With the irf740 , I really don't know why? but the S/N is better ...etc...
Take your time with good experimentation , it is better
Have a good time and saludos from Mexico
Alexis.

[bugwhiskers]

The attached .PDF files show the schematic and pcb that have been created with Eagle Light, the free version can be downloaded from the following link.
http://www.cadsoft.de/cgi-bin/downlo...le/program/4.1

JP6 is the header for connecting a LCD display with RN1 providing pullups for PORT0 of the evaluation board.
IC1, a 74HC4051 has eight caps for collecting 8 samples. JP1 is the header for the rotary encoder with the pullup resistors located on the satellite encoder board (Top right hand corner of pcb).
R19, R2 and Transistors Q1 & Q2 providing the level shifting required to drive an "N" channel MOSFET with the micro. D3 is a failsafe for protecting the micro if something goes wrong with Q1. When the micro is being programmed most of the inputs float, R7 is a pullup that ensures the MOSFET is off during programming.
L2 hasn't been tried but it is hoped a suitable choke can be found that kills off a lot of HF EMI.
JP8/JP10 is the header for the audio from the PWM.
The AD797 is a very low noise OP AMP and has some diodes in the feedback path which speed it up and also limit the excursions. If a germanium diode is used for D6 then the negative excursions caused by the TX pulse will be minimised allowing faster recovery.
C1, a 6800uF electrolytic supplies the current gulps required by the TX pulse.
The current setup requires 2 batteries. One battery of 8-10 volts to power the evaluation board via it's power socket and the other battery (absolute Max 16 volts) to power the coil circuitry. The postive of the coil battery is connected to the negative of the evaluation board battery and it's negative terminal is connected to JP2 with D1 providing reverse polarity protection. D2 provides a second negative positive protection for the LCD contrast with just a 1uF tantalum that is discharged fairly quickly by the LCD contrast adjustment pot. This setup is necessary as the LCD will eventually be destroyed if the contrast voltage is present when the LCD is not operating which would be the case if the power was turned off and the contrast was connected to the 6800uF cap.
All chips in the analogue part of the circuitry have their power supply pins low passed with 10 ohm resistors, tantalums and ceramic caps sited very close to the power pins.
The board has been designed to facilitate experimenting with 8 samples. There are risers on the board (JP10, JP7, JP5 etc) that take power and inputs/outputs to another satellite board that the user can make that hold filters/amps/ground balance/discrimination etc.
A predecessor to the current schematic was lashed up and worked well with very low noise. Many improvements/fixes have been made to this current version but have yet to be tested.
After the board is made and tested/finalised I will post the extensively commented software to drive it.
regards
bugwhiskers