complete project

[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]

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.

[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

[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.

[satdaveuk]

Thanks Tinkerer your a gent

Regards

Dave

[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

[Tinkerer]

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....

Alexismex, thank for the feedback.

The AD654 seems to be a step in the right direction.


What about using a Digitac Direct converter, like the AD9837. It produces a sine wave that is easy on the ear and frequency modulation.

Tinkerer

[Tinkerer]

Thanks Tinkerer your a gent

Regards

Dave

Remember that this is just a simple basic design. You notice that the motion version is nearly the same as the non motion version.

Now we can take this basic design and adapt it for a specific purpose, for example a pin-pointer.

There are lots of improvements that can be done on a pin-pointer design.

And many different choices. For example, it can be made autonomous, everything incorporated in a stick. No cable. Or it can be made as an attachment to a normal detector. Or it can be made with a short cable and attached to the upper digging arm.

Many variations are possible.

Then there are the possible variations of target indication. For example a vibrator, like cell phones use.
It needs some thinking of how to make the indicator with an autonomous just a stick design.

So, basically lots of thinking and figuring out to do. Too bad that only few people have a thinking hat.

Thinkerer

[Tinkerer]

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

Davor, thanks for the tip of the AC coupling of U4a.

There are other areas of improvement possible.

For example, the integrator- difference amplifier at U1d. The inputs are uneven because of the low impedance of the minus input and the high impedance of the plus input.
Maybe using a 2 opamp instrumentation amplifier design would bring some improvement.

Or divide the function into 2 parts, separate integrators and then an instrumentation amplifier to remove common mode noise.

What do you think?

Tinkerer

[pelanj]

I am still working on my audio PIC - it will use either one tone, which would shift up or down with the voltage at the ADC input or a two tone, low for iron, high for non ferrous mixed together. I think about using the PWM and some 32-64 level lookup table for the sine. It will be programmed using XC8, as that one is the easiest for me. I cannot promise any dates, but one day, it will come. Once I have the first version, I will post the code for comments and improvements.

[Tinkerer]

I am still working on my audio PIC - it will use either one tone, which would shift up or down with the voltage at the ADC input or a two tone, low for iron, high for non ferrous mixed together. I think about using the PWM and some 32-64 level lookup table for the sine. It will be programmed using XC8, as that one is the easiest for me. I cannot promise any dates, but one day, it will come. Once I have the first version, I will post the code for comments and improvements.

Thank you for the update.
It sounds good. Probably it is a good idea to try any execution as soon as possible to see how it works with the complete circuit.

The sine wave does not need to be very perfect, anything is better than a square wave.

Tinkerer

[pelanj]

I will test how the audio responds to a pot on the low pin count demo board. And you are right, even low precision sine is better than square. If the PIC is able to do a high precision sine generator (I have seen some projects like that). Once I have the sound generation right, it can be used instead of the hardwired VCO.

[mickstv]

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

Aziz

Hi Aziz, I can see what your talking about.



Mick

[6666]

pelanj

what type of PIC are you using ?

[pelanj]

I use what I have at my hand right now - that is 16F690. All I need is ADC at the front and PWM output. Some free digital I/O pins could be used to select different modes, use as mute or something like that. This one should be powerful enough with enough memory as well - but once the program is ready, we can try to squeeze it into some lower model if 16F690 would be overkill.