Simplest PI detector possible?

[Waikiki_Sweep]

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

http://www.ti.com/lit/ds/symlink/tl072.pdf

High Slew Rate . . . 13 V/μs Typ

http://www.ti.com/lit/ds/symlink/tl082.pdf

High Slew Rate . . . 13 V/μs Typ

It is hard to find difference between them in data sheets.
Even noise vs. frequency chart they just copied from one datasheet to another. NOBODY EVEN MEASURED IT EVER!!!

Looks like TL082 is made for marketing purposes only Same old stuff with new name.

If digging hard some more difference may pop-ups like offset looks better for 072 instead of all advertising.

That's surprising!!!

Usual capitalists scam!!!!


I think that real problem is: we trust those datash*ts too much To choose best OpAmp is good idea to test it in your device not reading ads.

[Davor]

Actually TL072 and TL082 are the same, except that wafers that do not pass strict criteria go into 082 and the better ones go into 072. Regarding noise and AC they should perform equally well.

[Waikiki_Sweep]

[OPA2350] 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

Yep. You are right. At low frequency like 10 Hz noise is too high. (Also LM318 and LF357 [Delta pulse] used in many popular PI schematics as preamps have HORRIBLE noise at 10 Hz - 60...300nV/√Hz )

Because I am looking for dual low noise with single supply 5V opamp I think I can use ISL28291 ($2.79 on Digikey)

Slew Rate 17 V/μS

8 LD SOIC (I Can solder it with good reading glasses )s

• 1.7nV/√Hz input voltage noise at 1kHz (2.5nV/Hz for 10Hz )
• 1kHz THD+N typical 0.00018% at 2VP-P VOUT
• Harmonic Distortion -76dBc, -70dBc, fo = 1MHz
• 61MHz -3dB bandwidth
• 630μV maximum offset voltage
• 3μA input bias current
• 100dB typical CMRR
• 3V to 5.5V single supply voltage range
• Rail-to-rail output
• Ground Sensing

These amplifiers have outputs that swing rail-to-rail and an input
common mode voltage that extends to ground (ground sensing).

The ISL28191 and ISL28291 are unity gain stable with an
input referred voltage noise of 1.7nV/√Hz. Both parts feature
0.00018% THD+N at 1kHz.

http://www.intersil.com/content/dam/...n61/fn6156.pdf

Any objections?

[Davor]

You are aware that 390ohm is the actual input resistance of this PI device, and it is in fact the equivalent resistance for 2.5nV/sqrt(Hz)? Perfect choice

[mickstv]

Yep. You are right. At low frequency like 10 Hz noise is too high. (Also LM318 and LF357 [Delta pulse] used in many popular PI schematics as preamps have HORRIBLE noise at 10 Hz - 60...300nV/√Hz )

Because I am looking for dual low noise with single supply 5V opamp I think I can use ISL28291 ($2.79 on Digikey)

Slew Rate 17 V/μS

8 LD SOIC (I Can solder it with good reading glasses )s

• 1.7nV/√Hz input voltage noise at 1kHz (2.5nV/Hz for 10Hz )
• 1kHz THD+N typical 0.00018% at 2VP-P VOUT
• Harmonic Distortion -76dBc, -70dBc, fo = 1MHz
• 61MHz -3dB bandwidth
• 630μV maximum offset voltage
• 3μA input bias current
• 100dB typical CMRR
• 3V to 5.5V single supply voltage range
• Rail-to-rail output
• Ground Sensing

These amplifiers have outputs that swing rail-to-rail and an input
common mode voltage that extends to ground (ground sensing).

The ISL28191 and ISL28291 are unity gain stable with an
input referred voltage noise of 1.7nV/√Hz. Both parts feature
0.00018% THD+N at 1kHz.

http://www.intersil.com/content/dam/...n61/fn6156.pdf

Any objections?

Looks ok.

Have you considered using a second stage on your frontend like the HH2, this will help you to sample earlier.

[Waikiki_Sweep]

Looks ok.

Have you considered using a second stage on your frontend like the HH2, this will help you to sample earlier.

Technically it is possible but it will add one more stage to the schematic.
How many microsecond you can win if two stages used? Looks like not much, 1,2,3 microseconds.
New OpAmps are fast enough to move from saturation quick (instead of that TL072).
Is it good idea to amplify top part of decay curve because it is most unstable part of signal?

Building a fast coil is much better way to get early sampling. As well as isolation of MOSFET capacitance with fast diode and use of short cable with low capacitance.

Also this tread is about "Simplest PI detector possible".

I love the idea to keep stuff simple:

- less parts to buy
- less holes to drill
- less soldering

that is what guys who build detectors at home dreaming.

I personally believe that any pretty good PI detector can be simplified with new technologies:

1. Heavy and complicated timing circuit can be replaced with any cheap and easy to program microcontroller (pic, tiny, ardiuno)
Also it can add unbelievable flexibility to timing so you can change TX and sampling sequences anyhow you want like for target ID sensing or ground balancing.

2. New single power +5V OpAmps helping to remove voltage inverter and all that transistors for voltage level converters between OpAmps, switches and microcontroller.
Making it as simple as possible.

By moving this way you can simplify SurfPI, GoldScan or any other PI making it works like original but 2-3 times smaller schematic and easy to build.

[bernte_one]

here it is
[ATTACH]27914[/ATTACH]

@ 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

if i mount a irf630 instead of mje13007 how should i rotate the irf630 the conection is total different right

[6666]

Hi WS and Mickstv, Looking back at some of Moodz's early projects he uses ca3130n as a single supply preamp, but I dont know anything about them.

[Thomas]

if i mount a irf630 instead of mje13007 how should i rotate the irf630 the conection is total different right

no rotation, same pinout, but the driver should be changed

[bernte_one]

ok assembled all together and gues what - nothing
only one light klick when i switch it on
over 10V supply MJE13007 gets hot fast


any hints i dont know

[mickstv]

Technically it is possible but it will add one more stage to the schematic.
How many microsecond you can win if two stages used? Looks like not much, 1,2,3 microseconds.
New OpAmps are fast enough to move from saturation quick (instead of that TL072).


Also this tread is about "Simplest PI detector possible".

On my test board with two stage, the difference between 100x and 1000x is about 4us. Thats running on 7 volts and about 140us TX pulse into parallel low RDS Mosfets and 10 inch coil (.4 ohms).

Is it good idea to amplify top part of decay curve because it is most unstable part of signal?

Using the normal protection method i.e. 1 resistor and 2x diodes the first stage amp is going to amplify everything at once.

[bernte_one]

has anybodody testpoints for me that i can measure?

[Eddy71]

MOSFET need more voltage on gate for working. I test IRF740. It work if power > 12V.

[bernte_one]

thanks Eddy

i have irf740 and irf630 here i replace R5 with a bridge and try it
what dou you think from the rest of my pcb
http://www.geotech1.com/forums/attac...4&d=1389733230

do you have any improvements ?

regards

[nick holas]

hi all
beautiful pcb
i m looking too for a pinpointer
how about your test ? (deep,sens etcc)
have made it but russian pcb with lm358 wire adaptation (not very good) and it don't work (doing crakling sound every time,any detection,can't tune it ),
so before i do your pcb could you tell me more.
(doing pickini at the same time with problems too!!!!)
thanks