PI Audio

[h9361]

As mickstv said, attempting to discriminate on a PI using target conductivity is a fruitless task.

Hello
Dear Qiaozhi.
Please forgive me for my question.
Have you ever received any report for best damping value of 320-350uh coil (Hammerhead)?
Thanks.

[h9361]

Here is a great little VCO circuit Mickstv posted back 2-3 years ago and I've had veroboard version for use on my bench for so long..it finally gave out so I decided to put it onto a PCB.
I added extra decoupling, changed Fet and added option for audio amp connection..all vanilla stuff.

Had 10 Blank PCBs made by PCBway for $25 Au and $20 of that was delivery.. Thanks for the heads up on that Moodz.

I normally use a digital audio version of this but sometimes analog is a better fit and Mick's circuit was worthy of a pcb
It is SMD using mainly 0805 parts.

[ATTACH]45385[/ATTACH]

The original circuit is posted in the Minipulse Audio section..

Cheers
Mdtoday

Hello
Dear Mdtoday
I have a request, i hope you accept it.
Is it possible to take a test video from your audio part?
Thanks

[Qiaozhi]

Thanks dear mickstv for your guiding.
I want to add GB part to HH1 with Mr. Mdtoday's Audio schematic. I hope i have different audio frequency than different metals so that i can almost discriminate metals.
Please see attached, it belongs to one user that tested different metals in Oscilloscope.

[ATTACH]55118[/ATTACH]

As mickstv said, attempting to discriminate on a PI using target conductivity is a fruitless task.

[mickstv]

Thanks dear mickstv for your guiding.
I want to add GB part to HH1 with Mr. Mdtoday's Audio schematic. I hope i have different audio frequency than different metals so that i can almost discriminate metals.
Please see attached, it belongs to one user that tested different metals in Oscilloscope.

[ATTACH]55118[/ATTACH]

I suggest you start a new thread for help regarding this one.

Looks like something Moodz was playing with maybe ask in the corresponding thread...

BTW in reality it's next to impossible to accurately discriminate using PI, objects at different orientations have different TC....

[h9361]

Your better off having your gain control on the preamp...

This circuit has set values for a reason, the first opa1642 has to be adjusted to 0mv output with no signal input otherwise the output won't work correctly. So a gain control in these stages will cause a offset issue with the circuit....

BTW. I've been using this circuit for a few years and works fine....

Thanks dear mickstv for your guiding.
I want to add GB part to HH1 with Mr. Mdtoday's Audio schematic. I hope i have different audio frequency than different metals so that i can almost discriminate metals.
Please see attached, it belongs to one user that tested different metals in Oscilloscope.

[Elliot]

See TDI PCB.[ATTACH]55104[/ATTACH]

Thanks H9361, but I was only referring to breadboarding an alternative audio section, not an entire TDI.

[mickstv]

Actually, i want to put a pot over my unit like TDI for controlling GAIN.

Your better off having your gain control on the preamp...

This circuit has set values for a reason, the first opa1642 has to be adjusted to 0mv output with no signal input otherwise the output won't work correctly. So a gain control in these stages will cause a offset issue with the circuit....

BTW. I've been using this circuit for a few years and works fine....

[h9361]

What do you mean by "gain pot" ?

Actually, i want to put a pot over my unit like TDI for controlling GAIN.

[mickstv]

Thanks. Do you think i can put a GAIN Pot in Mr. Mdtoday's schematic?

What do you mean by "gain pot" ?

[h9361]

You don't need and circuit after c19 on the HH

Thanks. Do you think i can put a GAIN Pot in Mr. Mdtoday's schematic?

[h9361]

I had a look at the TDI-SL circuit. I think a simpler version (less components) may be possible. I agree with your comment about the risk of a "lively" audio threshold, but we deal with those in all-digital machines these days (eg NOX). A way around it is to have an adjustable width dead band, or to wind back ones' threshold a bit. I'd like to give it a go on my breadboard if you can come up with a potential design solution.

See TDI PCB.

[Elliot]

Should be possible using a circuit similar to what the TDI-SL has. I'll see if I can figure it out. Realize though that by making the VCO more responsive near the balance point you will end up with a much more "lively" audio threshold.

I had a look at the TDI-SL circuit. I think a simpler version (less components) may be possible. I agree with your comment about the risk of a "lively" audio threshold, but we deal with those in all-digital machines these days (eg NOX). A way around it is to have an adjustable width dead band, or to wind back ones' threshold a bit. I'd like to give it a go on my breadboard if you can come up with a potential design solution.

[mickstv]

Thanks.
Your mean is after C19 or before it?

You don't need and circuit after c19 on the HH

[h9361]

No pin1 of IC8a. Forget about the HH sat, the rest of the circuit has a manual threshold control, which is better for small target detection.

It's easier to do three samples the you only need one integrator.

S1 about 5us, S2 130us and S3 125us all approx. Then you adjust the delay between S1 and S2 to ground balance

Thanks.
Your mean is after C19 or before it?

[mickstv]

Thanks, your mean after SAT (after SW2)?
Yes, i'm going to add GB with S1,S2 and two EFE

No pin1 of IC8a. Forget about the HH sat, the rest of the circuit has a manual threshold control, which is better for small target detection.

It's easier to do three samples the you only need one integrator.

S1 about 5us, S2 130us and S3 125us all approx. Then you adjust the delay between S1 and S2 to ground balance