Let's made a PC-base metal detector with usb interface !!!

[Aziz]

Hey PJ,

that was a nice trick to get some more motivation from you. Thanks mate!
I'm fully motivated again.

It seems, that I'll have the "World's Hyper Quietest Metal Detector Front-End Ever"(c)(r)(tm). 3 - 6 (or 4 - 8 ) transistors and enough spare for the worst cases. *LOL* I get really a parallel BJT disorder... *LOL*
Where are my f****** blue pills?

Cheers,
^sif

[Davor]

Blue pills are for sissies - take the red pill!
Look at me - I'm even wearing a fedora.

BTW, base degeneration works almost as good as emitter degeneration. It promotes Miller effect, but if you use RF transistors that's working just fine.

[Aziz]

Ultra-Low-Noise AC Amplifier

Hi all,

look what "blue pills"(tm) have done for me!
(BTW, it's not Viagra(tm)! )

This is the NPN and PNP version of the ultra-low-noise AC amplifier. It is fully tested. I'm providing you a fully working LTspice simulation files for your convenience too (see the zip-file below).

I'm going to use the PNP version for the next detector controller version (Class-E TEM/TEM V2.0). PNP transistors are more quiet. Targetted gain: approx. 100 times, RG2: 620, RG1: 4.7 - 6.2 Ohm.

Schematics of the NPN-Version:


Schematics of the PNP-Version:


LTspice Zip-file:
Ultra-Low-Noise-AC-Amplifier-4212.zip


Cheers,
4212

[WM6]

Aziz, thanks for design.

Do we need to discuss low noise coil design, that suit to this preamp, too?

[Aziz]

Aziz, thanks for design.

Do we need to discuss low noise coil design, that suit to this preamp, too?

Hi WM6,

I think, this isn't required. I'm going to use the "Top-Hat"(c)(r)(tm) anti-interference (AI) induction balance (IB) coil.
Larger TX (20 cm - 40 cm), smaller RX (8 cm - 16 cm, RX+/RX- in series). The total resistance of the RX coil must be smaller than 10 Ohm. The total RX inductance is around 1 mH. The residual induction inbalance RX signal (TX -> RX) may not exceed +/- 20 mV (+/- 2 V/gain = 2V/100 = +/- 20 mV).

The TX coil part will be speficied then.
Cheers,
Aziz

[sled]

thanks for sharing the design! I have a question although - my sound card has a full range input of 1Vrms at 0db (line-level) - so is there any attenuation of the signal necessary? If the RX signal exceeds 10mV then there amplified signal will be clipped by the sound card or am I wrong?

[Aziz]

thanks for sharing the design! I have a question although - my sound card has a full range input of 1Vrms at 0db (line-level) - so is there any attenuation of the signal necessary? If the RX signal exceeds 10mV then there amplified signal will be clipped by the sound card or am I wrong?

Hi sled,

yep, the input will be very likely clipped (due to hard wired high voltage protection circuit). Even if you make use of the input attenuation feature. And that (the clipping) isn't good for signal processing.
Well, in this bad case, one have to reduce the residual RX signal induced from the TX coil by a better induction balancing or one have to reduce the amplifier gain.
Aziz

[sled]

Hi sled,

yep, the input will be very likely clipped (due to hard wired high voltage protection circuit). Even if you make use of the input attenuation feature. And that (the clipping) isn't good for signal processing.
Well, in this bad case, one have to reduce the residual RX signal induced from the TX coil by a better induction balancing or one have to reduce the amplifier gain.
Aziz

Hmm... what about using the second stereo channel output to bias the amplifier so that the imbalance is cancelled by applying a phase shifted TX signal? (Found a patent here: http://www.google.st/patents/US5729143)

[Aziz]

Hmm... what about using the second stereo channel output to bias the amplifier so that the imbalance is cancelled by applying a phase shifted TX signal? (Found a patent here: http://www.google.st/patents/US5729143)

Why not sled. You can do that. I've already done that with the second output channel too. Either biasing the amplifier (summing signals) or a single turn auxiliary coil at the RX position to induce a compensation signal into the RX coil. Notice, it works perfect for a single frequency compensation. Multi-frequency compensation is going to be non-trivial as each frequency requires its own phase and amplitude compensation signal.

But we don't need it. Keep it easy and simple (KISS-principle).

We can reduce the residual RX coil voltage by several means:
- Shielding RX and TX coil seperately (no electric field induction from TX into RX coil)
- Graphite shielding (no AL-foil, no metal mesh)
- Reduce the metal content nearyby the coil (plastic bolts, plastic stem, litz-wire for the TX, relative thin wire for the RX)
- Usage of appropriate coil designs, which allow a very fine induction balance feature and are still easy to make.
I'll show some anti-interference (AI) induction balance (IB) coil options soon.

We can live with some residual RX coil voltage however.

Cheers,
Aziz

[Aziz]

Coil Design 1: Planar-Offset AI IB CC Coil.

Hi all,

this is a modified standard concentric co-planar IB coil with the anti-interference (AI) and truly fine balance feature. And it is much easier to build this coil compared to a standard concentric co-planar coil.

Once the distance gap (mm range) between BX and RX+ and the number of turns count for BX has been found for a specific distance of RX- to the coil, the induction balance can be precisely done (fine induction balance) by varying the distance of RX- to the coil.

RX+ and RX- has the same geometry and same turns count (=identical). They will be placed at opposite winding direction to cancel the EMI noise.

See picture below:


Pay attention to the coil winding directions.

Cheers,
Aziz

[Aziz]

Coil Design 2: Planar-Offset AI IB Modified Top-Hat Coil

This is also possible.


Pay attention to the winding directions.

Cheers,
Aziz

[Aziz]

The Ultimate Thermo-Nuclear VLF Metal Detector Controller! *LOL*

Hi all,

this is for all the guys out there wishing to experiment with pure digital (DSP) VLF detector design (Netbook/Tablet PC/Laptop + Sound Card). It consists of 5 passive parts only and does not need more electronics.
You have to process both signal channels however.



Hey sled!, you probably could use it for a warm up experience. This little circuit is really nice to start with.

Cheers,
^sif

PS: The LTspice simulation zip-file:

[Aziz]

+++ Breaking News +++ Yeah!

Hi all,

I have been informed by my bailiff today, that I've got a new "arrest warrant"(perverted tm). It's dated from 06.06.2013 (F***!, why I haven't been informed earlier?) . I'm looking forward to get my a.$.$ into the kraut court next week and get my personal copy of it. Yeah!!!!


Nice, I'm a collector of arrest warrants. *LOL*
I've told the bailiff, that I would like to go into the jail rather than to allow stealing me!

It's not an April joke!
I'm excited!!! I'm excited!!! I'm totally excited!!!
Cheers,
^sif,
see you in the jail... *LOL*

[sled]

ouch! better take care of that sh*t, we need you here

Thanks for the ultra simple detector interface, I'll try that one for sure this weekend!

By the way - I started designing my own sound card with a plug & play connector for your PNP amplifier circuit. A colleague of mine suggested to get some free samples... ordered yesterday and the parts are already on the way with FedEx - for free, I even told them the truth what it is for but it seem's like they don't really care

(here's a nice list of manufacturares which provide free samples: http://www.ladyada.net/library/procure/samples.html)

The idea is to use some good quality audio codecs with a PCM/I2S interface and proxy them over using an ARM cortex processor that acts as an USB Audio Class device. It's a lab/development board and not the poor man's metal detector for outdoors, but hey actually most of the parts were for free ^^

I'm not quite sure whether I should go for a fully differential audio codec or a single ended on, what do you think Aziz? I think the differential one could yield a better SNR...

The best candidates are so far:

CS4272 from Cirrus Logic (fully differential ADC/DAC): http://www.cirrus.com/en/products/cs4272.html

or

TLV320AIC23B from Texas Instruments (single ended ADC/DAC): http://www.ti.com/product/tlv320aic23b


PS: I ordered multiple of these, so if I get it done I can send you one

[Aziz]

My possible new Hotel. *LOL*

Look, where I will get my new comfortable full board Hotel:
https://maps.google.de/maps?q=Justiz...lt+Bernau&z=12

A nice place with nice sea (the famous Chiemsee) & mountain view to the Austrian alps.


It costs only 70 - 80 EUR per day. Oh yeah, the criminal thieves have to pay for my comfort of course!


Can't wait for my holidays. Yippie ya yeah!!!

^sif,
see you there.. *LOL*