Simplest PI detector possible?

[bernte_one]

some news
think it is good pi pinpointer

[Waikiki_Sweep]

TX from SurfPI looks even more simple. 555 drives MOSFET IRF9640 without any transistors. Also 8 pins dual Rail-to-Rail OpAmp like OPA2350 is perfect for the job. But proper conversion of schematic is required.

[6666]

WS what other projects have you used a OPA2350 in ?

[mickstv]

WS what other projects have you used a OPA2350 in ?

Really poor spec's makes it hopeless for a frontend amp. At 10khz has about 7nV/√Hz and below 10hz looks to be well over 100nV/√Hz

[Waikiki_Sweep]

WS what other projects have you used a OPA2350 in ?

I am experimenting with OPA2350 to build Ardiuno PI or front end for any Attiny / Atmega MC.
That OpAmp is good enough to use as preamplifier and integrator too because it is dual OpAmp
with low noise, high slew rate and an input common-mode voltage range that extends 300mV below ground
and 300mV above the one 5V positive supply.

Most interesting that it is one power supply 5V Rail-to-Rail OpAmp with ability to work with input that goes over the rail voltage.
It fits our situation when flyback voltage goed down to negative values over the ground rail but can be amplified by OPA2350 without additional -5V power supply.

http://www.ti.com/lit/ds/sbos099c/sbos099c.pdf

WIDE BANDWIDTH: 38MHz
HIGH SLEW RATE: 22V/μs
LOW NOISE: 5nV/√Hz

So you can hook it up to your coil without using -5V converter to make negative power supply voltage



and use second amplifier in case as integrator.

[bernte_one]

i have modified pirate pi pcb tl082 version to dimension of 25mm*75mm
will test and hope it works

[bernte_one]

here it is


@ all please check for errors copared to shematic
didnt test it
the place for the C8 1000uf is a bit to small for a standing cap
idea was to lay it down

please look an comment if something is wrong i am new in pcb desgin

[Waikiki_Sweep]

Flyback voltage trimmed by diodes goes straight to amplifier. No gating, no switches.
I think that scehematic will be more stable if you will use Shottky diode to trim flyback instead of 1n4148 or kd521 to lower input spike from 600-1000 milivolts to approximately 100.
Because if you will trim all the voltage let say more 100 milivolts than detector will ignore most of the spike and amplify more useful target decay signal.
Only problem with low forward voltage Shottky diodes is high capacitance. I found one DFLS130L with only 75pF. ($0.49 on Digikey)
It will cut everything that was over 100 milivolts working virtually as a switch that is absent in the schematic.



http://www.diodes.com/datasheets/ds30492.pdf

[Thomas]

Well done, I found one thing I would have done different but it isn't a big deal. I didn't see any problems, I noticed you switched a Darlington in .

[bernte_one]

hello thomas you are right

i build pcb from left to right, stretched it und shorten it here and there
so it is an improvement the resistor will be placed clother to tl082
thanks

[nick holas]

Hi all
Hi bernte good modification for tl082 (k157ya2 is impossible to find for me)
Bernte how about your test?
Does it have a good distance detection?

[kt315]

K157UD2 has nothing of something fantastic data. it is ordinary universal opamps. change it on LM358.

[Waikiki_Sweep]

Also you can try TLE2072. It is finally improved version of 30 years old TL072 - less noise, high slew rate, e.t.c. http://www.ti.com/lit/ds/symlink/tle2072.pdf
TL082 and TL072 are practically the same. It is hard to find difference between them in data sheets.

[nick holas]

Thanks all
I m going to try with lm358 and tl082 because i ve got them.
Does bd911 is good replacement ( yes , i know you will say :look at the datadheet) for irf740 or mje5742 ?
Thanks

[kt315]

TL082 and TL072 are practically the same.

TL082 better than TL072, TL072 better than TL062 - compare their slew rate.