Universal PI Micro

[okantex]

and something else
do you feed just positive signal to mux.
cause you can not feed negative to adc.

[bugwhiskers]

Hi okantex,

The signal that is presented to the analogue discrimination circuitry must range between ground and the +5 of the Op amps/Micro.

Take the first sample when the decay curve is at about 0.5 volts and the second one at 0.27 volts. The second sample is amplified by 2 so the output at the final stage will be just above 0 volts. Any Steel bought near the coil will then cause the first sample to go above the second causing a negative output and exactly the opposite when the target is Gold or Aluminium or anything that is a better conductor than Aluminium. Use the position of the second sample to get the adjustment correct. Use 10nF caps and a pulse sample width of about 1uS.
I hope you are starting to get the idea of how it works.

regards
bugwhiskers

[okantex]

Hi Bug.
what is the voltage when preamp is in saturation.is it around 3.5v when there is no metal around the coil?

can you give timeing of your software.

[okantex]

and the biggest problem in my mind iswhat is saturation of premap?
how do you understand it is finished.what sort of process lets you understand it?

[bugwhiskers]

Hi okantex,

Tell me please, do you have an Oscilloscope ?

regards
bugwhiskers

[1843]

Hi okantex,

Tell me please, do you have an Oscilloscope ?

regards
bugwhiskers

Hi,
He have no oscope,

Regards

[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

[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.

[1843]

Hi bugw,

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

Regards

[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

[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

[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 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]

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,

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

regards
bugwhiskers