Universal PI Micro

[okantex]

if this circuit prepares signal for adc ,mean cut off negatif parts,that is okay.
otherwise why to use these opamp ,use directly adc .
sorry if ı said ssomeething wrong,As I mantioned before I am not electronition.

[Wirechief]

Where are you located Tex?

John Tomlinson,CET
John's Detectors

[okantex]

TURKEY
2 hıurs to ISTANBUL

[Wirechief]

TURKEY
2 hıurs to ISTANBUL

That is really interesting Tex and this is really a worldwide web! Well I'm very pleased to meet you and I hope all is well in Turkey. Are you trying to build PI metal detector? Ok good luck and God Bless you Tex!!!

John Tomlinson,CET
John's Detectors

[okantex]

thanks ,just trying to do some modifications.

[asguard]

Hi there bugwhiskers,

I guess a man is only as good as his word. You said you`ld forward the old files (in particular 245 board), as you stated in correspondence. Still haven`t received the files. Regardless of whether or not you view or state why one would bother, is really a mute point. The point is you gave your word and in writing, see in Quote below.

Look forward to receiving them.

Regards
Asguard

The attached is a video of the LCD screen showing 4 AtoD readings. I alternate between touching the adjustment pot contacts with a wet finger and removing it to induce noise so you can see it is actually working. The readings and screen are being updated about 200 times per second as indicated by the rapid changes with induced noise.
Notice how stable the readings are with the finger off.The resolution is 0.149 micro volts.

Re the older bus board, I do have all the files still in “Eagle” format and the last lot of source code.

Regards
Bugwhiskers
---------
Hi asguard

Will dig them up for you. You can download a free “light” version of Eagle from the web that will let you edit/print them and make photo tools. I really don’t know why you would bother though when the ADUC845 eval board is readily available and cheap and will achieve much more with a lot less noise.

Regards
Bugwhiskers


-----Original Message-----
From: email
Sent: Wednesday, 30 May 20078:40 PM
To: email
Subject: Re: UPIM


Hi bugwhiskers,

Thats an ok bit of footage. I had something similar happening in a slightly different field, with magnetic sensors scavenged off a disk drive. (just not with 4 lots of readings).

Could you please forward the older files, eagle format, or .pdf like the others if you have them converted if not, I`ll see if I can get the Eagle file viewer, and use that.

Thanks
asguard
--------------------------
Thanks Bugwhiskers,

Appreciate it. I guess, because its an evaluation board....no real reason, I just like the "non-eval board" one better. Maybe its got something to do with an old car analogy, like my old Ford 2door (not that I drive it these days, worked the motor in days when leaded fuel was aplenty, and cheaper around 45cents Lt, 351V8, solids lifters etc...lot of noise, but performed well), had a wireless/stereo in it never or hardly used it while driving...could go on... probably familiar with the scenario or heard similar stories before.

Best regards
asguard

Ako ne, mislim moge ako vidim ti mali matso/matcka na put moge ti dobiti butina, ili moge cola ti da pogazi. Smatriyish da bavloyse. ma nije vredu budala.

[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

[Wirechief]

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

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 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]

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

[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

[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]

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

[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.