My take on the HH2

[waltr]

Hello
Dear walter
I have a question about flyback voltage at tp2.
According to Mr. Carl's paper, his flyback voltage is between 100 and 300v. Do you think size of a coil can change the voltage? For exp, i tested it over my 9cm coil and it is 46vpp. Do you think it is normal? I also check my r11 and saw it is a bit warm.

Flyback Voltage PEAK is dependent on coil Inductance and the amount of Flux (current & on time) in the coil at time of turn-off not size.
Also, the MOSFET's Avalanche Voltage Rating will 'clamp' the flyback Voltage.

Typical flyback is 100-300V.
A bit warm is ok (can touch without burning your finger). What value is R11?

How are you measuring Flyback? Scope probe and scope input rated for high enough Voltage?
Scope fast enough to 'see' the very, very short flyback pulse?

[h9361]

Flyback Voltage PEAK is dependent on coil Inductance and the amount of Flux (current & on time) in the coil at time of turn-off not size.
Also, the MOSFET's Avalanche Voltage Rating will 'clamp' the flyback Voltage.

Typical flyback is 100-300V.
A bit warm is ok (can touch without burning your finger). What value is R11?

How are you measuring Flyback? Scope probe and scope input rated for high enough Voltage?
Scope fast enough to 'see' the very, very short flyback pulse?

Thanks for your replying.
Before, my R11 (1W) was not hot, but i could detect target but from low distance!!! Now, it's hot but i can touch it without burning.
Now, i'm using my 9cm coil and it can detect a simple nickel coin (2.5 diam) from 6-7 cm, a steel 8cm from 16cm, a steel 22cm from 22-25 cm.
After a lot of trying, i changed my Q3. Before changing, my R11 was cold, but now it's hot. What is interesting is that i could detect the distance with the same 9cm coil before changing Q3.
In fact, my problem was in use of bigger coils, 45cm or 22cm. they couldn't detect target from high distance. For exp, my 45cm coil could detect the 2.5cm coin from 1/2 cm!
I think that my TX part didn't work or worked faulty because my R11 was not hot at all, and my detection only was based on receiver part.
Unfortunately, i'm using a simple O-scope and am trying to buy a professional O-scope (Rigol 1102E, 100MHz, 400V, with two probes x1 and x10). Since my O-scope is simple, i have not still created a new thread. So, i'm waiting to buy the O-scope and then share pics of my TPs. I think my O-scope isn't fast enough and it shows incorrect flyback voltage.
Anyway, today i will test my HH over bigger coil and notify you.

[waltr]

This still should be in a new thread.
This is a HH2 thread not HH1......

[h9361]

Hello
Dear Walter
After alot of trying, finally i could solve my poor sensitive. Unfortunately, my IRF740 had a problem.
Now, i have an another problem! My threshold pot has not any affect over my audio (my HH1 is Rev. c2, op1). Other words, R31 can't set speaker to silence, i tried two values for R30 : 39K and 150K, the values didn't do anything. Do you have any suggestion for checking?

[waltr]

Hello
Dear Walter
After alot of trying, finally i could solve my poor sensitive. Unfortunately, my IRF740 had a problem.
Now, i have an another problem! My threshold pot has not any affect over my audio (my HH1 is Rev. c2, op1). Other words, R31 can't set speaker to silence, i tried two values for R30 : 39K and 150K, the values didn't do anything. Do you have any suggestion for checking?

AGAIN: this is an HH2 thread.
Please start a thread in the HH1 category

[h9361]

Hello
Dear walter
Please forgive me for writting here.
As you know, i'm working over audio part of HH.
First, i built non-vco version with unsheild coil.
It worked very stable, so i decided to test vco mode.
First, I tried to change its speaker to 8r but i could not.
Anyway, i had to use its original schematic with a 32r speaker. Now, i can hear its vco audio and my threshold pot is working but i have a new problem and that is noise or instability! What is intresting is that i had no any noise with my coil, even i can move it in air or up/down over ground without any noise. But its vco mode is very unstable and i can not move or up/down the same coil. Since you have a lot of experience about HH, do you think it is normal such noise between vco and non-vco? Has your HH2 any noise or instability?

[waltr]

I have been reading your other thread. kt And Carl has been helping.
No idea what your issue is. You must use your scope and troubleshoot where the noise is coming from.
It is possible that your PCB layout is the issue, this is typically the Ground connects. Study how I did the PCB on my HH2.
I posted the gerbers so download and open in a gerber viewer.

[h9361]

I unfortunately did not look at that schematic close and it has been a few years since I played with 4046 VCO.
I dug through my archives and found this:[ATTACH]55062[/ATTACH]

This is the one I played with. Mickstv is a user here on Geotech who posted this. Search for original thread about this VCO.

Other wise you simply need to build and experiment (well you need to do that anyway).

Thanks dear walter.
I have a question about mickstv's schematic. Do you think its ground is -vb or +vb if i want to add to my HH?

[waltr]

On the HH1 &2 Ground is the Battery+ and the +5 and -5 are centered on Bat+

[h9361]

Hello
Dear Walter.
I have a technical question about your HH2. I compared your HH2 with HH1 in one point, Gain of U5:A (your HH2) than IC8a (HH1).
I think your Gain is 450 but it's 100 in HH1. Can you tell me the increasing gain what effect it has?!
Thanks

[waltr]

I don't remember the full reason when I did this design.
There is also a gain of 4.3 (U13A & B) into the integrator stage (U5A) on each sampling switch. So total DC Gain is closer to 2000.
However, you need to read on how the integrator works (link below). This in reality does not have DC Gain. The 100k feed-back R discharges the integrating Cap C12 not provide DC gain. The integrator only works on a Changing input Voltage.

I'm sure I also decreased the pre-amp gain as stated in post #1 of this thread.
My schematic shows preamp gain of 1000 but I think it is 470. Also D2 and C3 are not installed on my board since these killed bandwidth to much.

I do remember running integrator simulation using Excel spreadsheet as per Carl's explanation of how the integrator works. See thread: https://www.geotech1.com/forums/show...tegrator-works
for details.

I did combine ideas from other detector designs. That is where the gain between the sample switches and integrator came from. I then spent a few months prototyping various designs before doing the final schematic and PCB. These also have many options to allow experimenting, some of which are not used.

[h9361]

I don't remember the full reason when I did this design.
There is also a gain of 4.3 (U13A & B) into the integrator stage (U5A) on each sampling switch. So total DC Gain is closer to 2000.
However, you need to read on how the integrator works (link below). This in reality does not have DC Gain. The 100k feed-back R discharges the integrating Cap C12 not provide DC gain. The integrator only works on a Changing input Voltage.

I'm sure I also decreased the pre-amp gain as stated in post #1 of this thread.
My schematic shows preamp gain of 1000 but I think it is 470. Also D2 and C3 are not installed on my board since these killed bandwidth to much.

I do remember running integrator simulation using Excel spreadsheet as per Carl's explanation of how the integrator works. See thread: https://www.geotech1.com/forums/show...tegrator-works
for details.

I did combine ideas from other detector designs. That is where the gain between the sample switches and integrator came from. I then spent a few months prototyping various designs before doing the final schematic and PCB. These also have many options to allow experimenting, some of which are not used.

Thanks dear Walter.
I have a request, is it possible to see attached (A1(s1-s3) - A2(s2-s4)).
Do you think gain of final stage should be 1 to do final subtraction or it's better like other 100?

[waltr]

Not really sure.
Why is there a 100uF cap on S2-S4 input?

With this method of GEB typically the GB sampling has a variable gain (panel adjustable) to set the GEB.
This can be the FB or input R.

[h9361]

Not really sure.
Why is there a 100uF cap on S2-S4 input?

With this method of GEB typically the GB sampling has a variable gain (panel adjustable) to set the GEB.
This can be the FB or input R.

Thanks, which 100uf? i can not find the cap.

[h9361]

Do you think i should put C39 or doesn't need?!