Universal PI Micro

[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

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

[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

[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]

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]

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

[Alexismex]

Hello BW Very good work do you think the ground change sometimes the electromagnetic pattern of the sample (cause dispersion).It is a good idea to check the adjustment of discrimination in air and in ground to see how is the response change.love your approach to resolve the discrimination, keep is simple like you are doing. have good job and day
saludos from Mexico
Alexis
sure many people are in anxiety mode because of the real challenge you are making.

[bugwhiskers]

Hi Wirechief,

The attached .PDF is the schematic for the discrimination board.

IC2 captures samples and stores the voltage on caps 1,2&3.
R22 is used to set zero volts at the output of IC4C with no target.
IC4D is used to remove sample 3 ground signal (C3 & IC3).
The un-named IC is an LM311 comparator. R18 sets the voltage trip point which is passed on to the micro to indicate metals either side of the "pivot point" as mentioned in earler posts. IC4D goes to the micros AtoD input to indicate signal strength.
All fixed resistors are 10K, all caps are 330nF except C1,2,3,13,14=100nF. The 10k/330nF combination was chosen to provide -3dB rolloff at around 50Hz to minimise mains hum interference. R22 is 50k and R18=500 ohms.
The pre-amp I am using is an LF356, it can handle driving 1500pF and produces a gentle sluggish curve rather than the steep drop off of faster types which suits this particular sampling method.

At the moment I am experimenting with sample positioning to determine the best timings to maximise discrimination.

regards
bugwhiskers

[Wirechief]

Hi Bugwiskers, do you have a pic of the setup and discriminator board to see? I appreciate it Bugs and I wish you success on this project. God Bless ya .

John Tomlinson,CET
John's Detectors

[bugwhiskers]

Progress report

Today I populated the disciminator board and took it for a test drive. After wasting over an hour trying to find out why the signal on the caps didn't look right I replaced the caps with the correct values (100 times what were used in the first instance by mistake) and it started working. The positioning of the samples is fairly critical, in fact I got it working and tried to improve it by moving the sample positions and it stopped working. It would appear there is a "sweet spot" where maximum difference will be achieved.
I even found a spot where Fe caused it to go slightly positive before going negative which is no use at all !
When adjusted correctly for zero volts with no target Fe causes it to go negative and Al positive. This signal will be fed to a comparator then onto the micro to indicate metal type cutoff point for the audio.

regards
bugwhiskers

[bugwhiskers]

Hi wirechief,

I'm not sure what Dave is doing re audio. The PWM output will drive a Piezo element directly and consumes miniscule power.
One thing I forgot to mention earlier is the output from the amplifiers that perform the discrimination will go to a comparator that tells the micro when a non Fe/Pb target is detected. The micro will then use an AtoD reading of the second sample to generate a rising pitch to indicate signal strength via the PWM.

regards
bugwhiskers

[Wirechief]

Hi Bugwiskers, isn't this the same type audio that Dave is using? Isn't PWM a lot easier on the batteries also? This is really cool that you are letting us see it step by step. Thank you Bugs .

John Tomlinson,CET
John's Detectors

[bugwhiskers]

Progress report

The ADUC845 chip has an 8/12 bit DAC which is being put to good use in providing an offset voltage adjustment for the pre-amp. In the 12 bit mode a resolution of 610 microvolts is possible over a range of 2.5 volts allowing very fine adjustment.
A rotary encoder kindly supplied by Dave Emery is in place, it allows changing internal variables like pulse width, sample delay etc.

The PWM to provide audio is now also functional, it has a 16 bit range 0-65535.

regards
bugwhiskers

[Wirechief]

Hi Bugs, I would say that fella sort of dumped on himself!

John Tomlinson,CET
John's Detectors

[bugwhiskers]

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