HH2 -- Take Two

[joecoin]

I'd like to have at least one please.

[Ray-NM]

new board

Any update yet Carl on the new bds and how well your test bd worked.
thanks
RayNM

[Nc-Dirty-digger]

was wondering if you got this working yet? im new have'nt built anything but have been reading about building for awhile now.and have become interested in trying to build one myself.this looked like a great place to start.i would be greatful for any help thanks

[Altra]

Finally had some time to get the HH2 going. Still have some tweaking to do. Did not complete the audio section, wanted to get the front end going first. I was lucky and found a 11in GP4500 DD coil on ebay, this will be my standard. Later I will wind my own coil. I didn't have a PIC12f683, so I used a PIC12F675. Its ok, but the internal oscillator only goes to 4mhz vs the 12F683's 8mhz. I going to order some PIC12F683's. Its on hold until after the holidays, hope some others report in soon.

Happy New Years Everyone!

mark

[johnandles]

Sequence of construction

Hi Carl my board arrived,wow!
Thankyou.
Is there a recommended sequence of build,adjust, test etc.
Have you started the Web site yet?
Cheers
John

[Altra]

I got to play with the HH2 again. The fet driver and the dual preamp design, really speeds things up. Kudos to Carl! I am sampling around 10uS, using a homemade 8in mono coil (220uh/1,4ohm). This same coil on a PI with a single 1000X preamp gain has to be sampled at around 20uS. So there seems to be real improvement! It can pick up a nickel at about 11in. Not a peep out of a small nugget(match head size). Still more work to do.

I was able to get about the same results with an 11in ML DD coil.

Someone asked me which part I was using for the preamp(IC6). I tried the MAX412 and the NE5532. Both work well, based on observing the output on the o-scope. The MAX412 seemed slightly faster. For those of you who don't want to pay $9 for the MAX412, the NE5532 at under $1 will be fine. You can always upgrade later.

Mark

[johnandles]

Adjustable delay

Hello Altra,
did you attach a pot to ADC pin and is that all?
If not I am a little unsure as whether you had to change Carls software as well.This area is new to me (micros).
Could you post what you changed or added to achieve adjustable sample delay?
Cheers
John

[Carl-NC]

The easiest way to change the delay is in the coded value. I think I documented how that works. I will add code for the pot in the near future.

[Altra]

Hello John,

Below is from Carls code. These five variables control all the timmings.


//--- Variables ---
unsigned int Period = 255-125; // 1000 Hz (PS=16)
unsigned int TxPulseWidth = 65535-100; // 100us
unsigned int Sample1Delay = 65535-15; // 15us
unsigned int Sample2Delay = 65535-200; // 200us
unsigned int SampleWidth = 65535-15; // 15us
//--- Prototypes ---

An example, you want to change the Tx pulse width from 100us to 60us:

Change this line
unsigned int TxPulseWidth = 65535-100; // 100us
to
unsigned int TxPulseWidth = 65535-60; // 60us

or sample delay to 10us

Change
unsigned int Sample1Delay = 65535-15; // 15us
to
unsigned int Sample1Delay = 65535-10; // 10us


I am using the adc to change the sample delay. I left out the details for
two reasons. First I do not program in C language. Second I modified my pcb connections to the pic chip that are slightly different than what Carl's specified in his modifications. I did this before his code or pcb changes were posted. So, I don't want to muddy up the project by confusing the details. Just follow what Carl posts.

mark

[johnandles]

Thanks Altra for the info,now I can change the firmware to adjust parameters and recompile.
I dont understand "C" either.
I hope Carl will post the adjustable version soon.
Regards
John

[johnandles]

lost my brain

Hello, I am not sure if I am reading the firmware correctly or not.
I assume the ..
#define TxPulse GPIo1 is pin 6 on the micro
but on both posted schematics it seems to me like pin 4(GPio3) is the Tx trigger?
I cant find a remark to Pin 4 pin assignment?
As I mentioned on previous posts that I am new to pic programming and only had minimal Basic with PC programming experience.As a learning tool this project is fantastic,I hope to gain knowledge,maybe someone can put me on the right track.
Cheers
(should have slept in)
John

[Stefano]

Hi Carl,

could you please confirm the following transistor replacement:

2N3904 -> BC547
2N3906 -> BC557
MPSA64 -> ??? (BC516??)

but soldering them 180° rotated.

Is that Ok?

[Altra]

John,

There was a problem with pin 4 on PIC12F683 it only functions as an input. So Carl changed the code and posted these modifications for the circuit board. GPIO3 was change to GPIO1 for the TX pulse. You need to cut a trace on the pcb and add a jumper

http://www.geotech1.com/forums/showthread.php?t=16101

You are correct about the "#define TxPulse GPIO1". This creates an alias for GPIO1 or pin6.

You should read all the posts under HH2. Also for a better understanding of the over all circuit read through the HH1 threads and original article

http://www.geotech1.com/cgi-bin/page...head/index.dat

[Carl-NC]

Hi Carl,

could you please confirm the following transistor replacement:

2N3904 -> BC547
2N3906 -> BC557
MPSA64 -> ??? (BC516??)

but soldering them 180° rotated.

Is that Ok?

I didn't look at the details of the replacements, but they are probably fine. These are just general purpose transistors, except the A64 is a Darlington.

- Carl

[johnandles]

Thanks Altra,It all makes sense now.
Thankyou
John

John,

There was a problem with pin 4 on PIC12F683 it only functions as an input. So Carl changed the code and posted these modifications for the circuit board. GPIO3 was change to GPIO1 for the TX pulse. You need to cut a trace on the pcb and add a jumper

http://www.geotech1.com/forums/showthread.php?t=16101

You are correct about the "#define TxPulse GPIO1". This creates an alias for GPIO1 or pin6.

You should read all the posts under HH2. Also for a better understanding of the over all circuit read through the HH1 threads and original article

http://www.geotech1.com/cgi-bin/page...head/index.dat