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Hi All!
This is my PILAB project.
All this schematics are at "alfa relase" and
before I deciding to realize the 3 - PCB I'm posting to this forum and
wait YOUR OPINION and YOUR EXPERIENCE.
As you can see, this is an ibrid cirquit, Digital-Timer + Analog Integrator.
With this method is moore simple to realize a great sensitivity PI detector at home,
without sophisticated digital instruments.
This is a blend of the better ideas that I've seen to the PI forums
plus some personal interpretation of the problem,
implemented using some of the best Operational Amplifiers (* see at bottom).
The main intent was to develop a stable, customizable and easy to use detector,
with some kind of discrimination.
I've see a lot of projects using the timing cirquit based on
R-C timer (NE555 and similar) and I think this is the main instability problem
and a grat limit to my design idea.
The second problem was how to eliminate the potentiometers from the timer
and from the integrator cirquit and tuning.
To do this you can benefit by the variable (presettable) duration of each event (TX-Delay-SAMPLE-Delay-GROUND)
in the resolution of one microSecond. Some software CTRL can adjust the OP output stage at non-saturated level.
The LCD make moore professional and intuitive the usage.
Using the microcontroller AVR ATMega16-32 You can implement the HEX file
programming on "C" language and using the IDE Enviroment, absolutely free!
I don't know if exist a "C" enviroment for MicroChip free (GPL).
The ATMega is the better choice, ready to upgrade the project at any level
(and you can see, the timing board is moore similar to a general-porpose
CTRL-Board, reusable in more projects).
The separate audio power is a must: you can grow the volume at maximum level
without generate noise at the other high-sensitive cirquits.
You can consider the benefit of a similar cirquit opto-isolated
for all the headphones used in the other projects.
This little box with an 9V transistor battery can improve stability on each MD.
If you like (or don't like) my idea don't forget this: i'm waiting your opinion!
You can obtain a copy of this schematic (realized with Eagle 4.11r2)
sending your request at
piproject(AT)italcalcolo.com
(replace (AT) with @)
so you can draw and implement directly on it. All was made for free, with NO PROFIT!
I'm ready to collect your opinion and your mods in this email-box piproject(AT)italcalcolo.com
(replace (AT) with @),
please use the same "eagle" format for schematics e ASCII text file for your opinions.
If you make some change to the main project,
please mark the mods with a dash-box and a brief description.
The new project-step will be annunced at this forum, free.
And yet a brief description for each schematic.
Timer Function:
Event controlled via quartz timer.
Full timing adjutable (TX-Delay-Sample-Delay-Ground) for
each channel. For each event a variable time-period with uSecond resolution.
Standard HD44780 LCD interface (used only for menu - control not for visual identification)
Simple Keyboard for event control.
Save - Restore for last setting and useful field setting.
Using the internal Flash memory you can define personalized
profiles up to fill 512 bytes of memory. Easy interface to 29xx
flash memory to upgrade the personal storage(port "C" pin 0-1)
SPI interface for OnBoard Program Upgrade, external DB9 connector
Optional dispatch via CD4017, need some different schematics but will be moore elegant
Analog Function:
DD DualCoil Ready - move some jumpers
Dual channel integration for separate parametric search
Long TX, Long delay, Long sample for Iron and ferrous metals
Short TX, Short Delay, Short sample for Gold, similar metals, very small objects.
Dual stage preamplification for better WideBand and low drift gain:
AD797 (one of the best UltraLowNoise, HiSpeed OP) and OP37 ( LowNoise, better singnal swing by the +/-5V)
Y configuration: CH1 Normal gain for Iron
CH2 max gain for Gold signal.
Ground balance (via some Microprocessor AD sampler)
Channel Separate - Autotuning - LowPass - Adj.Treshold signal amplifier
Summing amplifier (Iron + Gold Channel) for Full-Metal search.
Diff amplifier with visual led indicator (need your idea to implement a BEEP-BIP audio signal - Help please!)
Standard VCO via NE555 (derived from Carl-HH Project)
Audio Amplifier isolated via Optical, separate power.
Hard / Smoot click selector.
Power Function:
Stabilized rails via standard regulators.
Low pass P filter for noise elimination.
Low ESR capacitors (derived from CPU MainBoards switch regulator).
One battery pack.
Common StepUp converter with HiFreq switching, Positive Voltage Adj..
Low DropOut -10V regulator (better battery discharge)
TX Driver Voltage adjustable (-8 to -12V) and Microcontroller activable
Low consumption battery meter (I don't know if it will go!)
PS:
Special thanks to "Analog Device" and "Texas Instruments"
for the free sample kit that have send to me.
Two Great Company that help the research at any level!
If you buy an AD797 at normal resellers cost 20$ in Italy, while in the USA the same OP cost 5$!!!!!
Special thanks, for his help, to B.Nicola that have always no time.