Universal PI Micro

[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.

[okantex]

thanks ,just trying to do some modifications.

[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]

TURKEY
2 hıurs to ISTANBUL

[Wirechief]

Where are you located Tex?

John Tomlinson,CET
John's Detectors

[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.

[bugwhiskers]

Hi okantex,

Please review post number #179, the last paragraph in particular.

regards
bugwhiskers

[okantex]

with 3 caps projecet ,why do not you measure caps directly with adc .
why do you use opamps.
you can do opamps work with software.
you have to use micro to have precison timeing to control switch of caps ,so why to use opamps .
do it alone with micro as you did in 64 sampler method.
if you say "I will omit mıcrro controlled switch",that is okay then.

ye you are right I am suspiciuos of having right point for sampling cause I do not know how to understand that saturation is finished.
if I use a pin as clock reset which takes signal from preamp and then count a period and take example that could be much more table than using adc as clock starter.cause it wont need any caps to charge and read values.it will just say yes there is voltage.
rest is software and try and see style work.

can you help me to make 3 caps charging and leading to adc circuit.I think 40mhz 18f series than will be okay .
am I rigth

[bugwhiskers]

Hi okantex,

The 75v signal is the back EMF.

Somewhere along the real decay curve from the output of the pre-amp there will be a spot that is around 0.5 volts. Don't forget, it's the position of the second sample relative to the first sample that is important, the voltage has to be just over half of the first sample. I have no idea how you are going to find that without an Oscilloscope unless you lash up the circuit and use a high impedence multimeter on the caps.

regards
bugwhiskers

[okantex]

Hi Bugwhiskers,

"
Take the first sample when the decay curve is at about 0.5 volts and the second one at 0.27 volts.
"
what is the voltge at saturation period.
I looked at HH project .it is around 75v in osiloscop.
I got a view from 1843 it was around 3.5v

confusing is that how can you read 0.5 volts at the begining knee.

[bugwhiskers]

Hi oktanex,

The PIC AtoD will have it's own sample and hold cap and as long as the TX and sampling is being controlled by the micro it should be very precise.
If you want to do your own thing with a PIC and no oscilloscope I wish you luck. If you can afford the $75 for the evaluation board then it is a much easier way to go.

regards
bugwhiskers

[bugwhiskers]

Hi 1843,

I have been using an LF356 which is slow but gives a distinct curve rather than a fast drop from saturation. The exponential shape of the curve doesn't change so it should work almost anywhere on the decay curve where there is some signal remaining. Remember though, small fast targets disappear very quickly so it's probably better to sample early if that is what you are after.

regards
bugwhiskers

[1843]

Hi bugw,

An op amp with high slew rate is better or low?

Regards

[okantex]

Hi Bugwhiskers
I am textile engineer.So I am not familiar with elctronic terms.
It is okay now.I understand what is saturation.it is almost same flat line made by flyback cut-off diods if the voltage is high.
thanks for explanation.
but
my question is how to understand end of saturation period as precision point.to start sampling.
I know a way; it is measureing by adc of PIC but it is not precision method because it is imposible to get sample always from same point cause adc s are not fast enough to do this.

[bugwhiskers]

Hi oktanex,

If you can find the Hammerhead project page there are some nice Oscilloscope photos that show the flat top of the pre-amp in saturation.

The OP amps are fed with + & - 5 volts usually. Most OP amps outputs cannot swing to the full extents of these supply voltages. If the inputs are presented with a voltage that is too high for the OP amp to output then the output will flat top at it's maximum output voltage, this situatiuon is called saturation. This flat top is useless becaues it doesn't truly reflect the input voltage times the gain so any sampling must be done when the Op amp is out of saturation and operating normally in it's linear region.

Ebay often has second hand Oscilloscopes and they really are a necessity if you are going to do a lot of R&D work, without one you are "flying blind".

regards
bugwhiskers