complete project

[Aziz]

Well you had better send me some hotrock's then.

Ok Mick, take a flat iron plate and change it's orientation to the coil. Should show the same effect.

Aziz

[satdaveuk]

Thanks Tinkerer your a gent

Regards

Dave

[Davor]

IMHO you miss a capacitor in series with the noninverting input circuitry of U4a to fix all the offsets from the previous circuits.

Yes thats with the CRO connected directly to the receive coil. No diodes just a small damping resistor to reduce ringing.

Yes, that's the whole point of a step voltage source - it does not have a short lived exponential fall as PI does. I observed this very behaviour in my simulations right when I joined this forum, and wondered - how come that no one uses it ?!? My simulations used low voltage and symmetrical Tx supply with equal pulse durations on + and - side.
The catch is that targets present themselves as a loaded transformer, where a Tx coil's resistance/load is somewhat added to the target resistance/load. The damping resistor does that - it is transformed from a Tx coil to the target and appears as an additional series resistance, hence shortening the target tau. With Tx coil being attached directly to a voltage source, its resistance is the very resistance of copper wire, and that is not much.
Otherwise you can distinguish iron from, well, everything else. At best.

I believe this is a surefire approach to better detectors with discrimination.

[Tinkerer]

TINKERERS_SB_MO THE MOTION VERSION

attached is the schematic of the TINKERERS_SB_MO THE MOTION VERSION

It uses the same timing schedule and the non motion version. Again, the bare essentials, to be used for further development.

Attached also the HEX file for the PIC16F690.

Enjoy

Tinkerer

[mickstv]

mickstv,
thank you for posting the pictures. Could you or somebody post some pictures of standard PI wave forms, to see the difference?
Are you saying the wave forms you show, are before any amplification?
Monolith

Yes thats with the CRO connected directly to the receive coil. No diodes just a small damping resistor to reduce ringing.

[Monolith]

mickstv,
thank you for posting the pictures. Could you or somebody post some pictures of standard PI wave forms, to see the difference?
Are you saying the wave forms you show, are before any amplification?
Monolith

[mickstv]

Hey Mick,

now show us the "masking effect" of the targets. Make three measurements:
1. Gold nugget alone
2. Hotrock alone
3. Gold + Hotrock together.

Cheers,
Aziz

Well you had better send me some hotrock's then.

[Aziz]

Hey Mick,

now show us the "masking effect" of the targets. Make three measurements:
1. Gold nugget alone
2. Hotrock alone
3. Gold + Hotrock together.

Cheers,
Aziz

[mickstv]

Micks Target shot's

Hi All. I thought I had better show some of my target shots. These shots are taken from a second coil in a rough DD setup. The receive coil is only mono loop at the moment, for experimenting. and the cro shots are directly from the coil with no amp.

Nails and bolts show next to no response or if they do the cro shows a lower response.

I should also mention I had to change the 4.7nf cap to a 10nf cap to get the 7us pulse, I guess this is for the coil size I'm using.


Also my sub gram nugget measures a positive response, whilst a red house brick shows a negative response.



No Target




Lead Target




Steel Target

[mickstv]

Hi Tinkerer, I believe I've fixed the problem. Like you said the timing is opposite to normal PI. ATM I'm running the circuit with just a standard Mono coil from one of my other circuits and another mono roughly configured to induction balance and I can see definite changes depending on target type.

Next is to build a better coil.

I'm impressed......

[Alexismex]

all major pi fails for the audio circuit, we say that 3 o 4 years ago in the forum , we put a lot of efforts in the front end etc...circuits ..... but a very poor design audio , 50 mV too much ...first use a correct VCO you need a specialized circuit like a ad 654 and mix it with the treshold audio classic ....it is the best for me for audio....

[Davor]

Yes I see, so you actually wish audio to accent the small variation at ~10mV and at the same time you wish to maintain the convenience of the non-motion detector, and you are happy with some floating, yet the circuitry around U3a suggests otherwise.
Considering U3a being configured as a non inverting amp, with minimum gain being 1, and the feedback resistor R20 being nailed down to the ground, also being configured as a log amp IF input signal is referenced properly to the ground, you are actually quite close to your perfect audio. In case you do not oppose to turn U3a into a perfect PD controller, you could connect the R20 to a large grounded capacitor or a slow servo, and voila, your audio will gain a more edgy response for targets, and retain the proportional response for the baseline. You might want to pump up some gain in the preceding stages though, because without the target kick, it will revert to the unity gain.

BTW, the 50Hz problem is more of an input stage problem. Point is that input coil will pick 50Hz either as a differential signal by magnetic flux, or more likely capacitively as common mode signal. If it hits the switchers you'll have some nasty interference. Your input is a real differential one and it takes care of the common mode quite efficiently, but you might consider some differential mode highpass filtering - just in case.
Shortly, you'll fight 50Hz more efficiently with single HPF at the preamp than with heavy LPF further on.

[Tinkerer]

Noise-wise C18/C38, the first filtering stage plus a differenting integrator make sense, and more than that is just overkill, and will introduce some serious delays.
Audio stage can be improved by introducing some proportionality to volume. OK, you have proportional frequency, but in absence of targets you could enjoy some privacy
How about a simple twin T at the audio output, say, in series with R4?

Thanks for the feedback.

About the noise filters: Inside the house, the open breadboard picks up the 60Hz noise on every wire lead. The filters really help there.
Inside a shielded box this would be different and some of the filters will become redundant.

However, one keeps hearing about detectors that are much affected by mains noise, so I really don't know. It needs testing of the final product.

The audio. I can say it works, but it is not where I want it yet.
As is, the target signal needs to be about 50mV or more to be discerned. I would like it to be about 10mV.

The differentiation between FE and gold is easy to hear.

The flexibility of the floating "center" frequency is nice too. It gives some leeway for the ground variation.

The continuous tone is annoying. A tween T filter at the center frequency would help for that. Adding a target volume response would help a lot.

I think pelanj is working on that.

The speaker has a resonant frequency where it is louder.

The square wave makes a horrible sound. The problem of a filter, to take the edges off, is the variation of the frequency from 50 to 1000Hz. Of course it can be filtered, but it gets quite involved and the idea of this specific circuit is to keep it extremely simple.

Tinkerer

[Davor]

Noise-wise C18/C38, the first filtering stage plus a differenting integrator make sense, and more than that is just overkill, and will introduce some serious delays.

Audio stage can be improved by introducing some proportionality to volume. OK, you have proportional frequency, but in absence of targets you could enjoy some privacy
How about a simple twin T at the audio output, say, in series with R4?

[Tinkerer]

Actually it is more of a step voltage than a TEM, but does the same job, and step is more PI like. Call it as you wish, but we have finally something new on the block.

My suggestions would be to reconsider the level of filtration throughout system. You have incredible number of filtering stages, and you know about "too much of the good stuff". For starters I'd remove C33 because of the changing impedance of that particular circuit. Then I'd continue removing R14, C26 and R45 (offset is fixed elsewhere already).

My focus recently is on the differential inputs, such as yours. Nice job

Davor, thanks for the feedback.

I agree on C33, C26, R14, R45. It will work without that. The reasoning is to use always the minimum bandwidth needed.

Will it make a difference? Only trying we will really know.

Tinkerer