Step 4 flyback voltage of 240v

[Denots]

Hi,

I also bought geotech baracuda board and I am building it. I do like you design. It's really nice.
I just measured for U4 pin1 and 4. They really look like yours. (I don't know why I can't upload my screenshots, I can only add images from url)
So maybe you or we are good to go.
Here I have very short depths of detection, I am guessing my damping resistor isn't right.
I read previous posts and also inside the metal detector second edition.
And now I am just waiting for more 2W resitor values. I'll let you know if I can make it work as expected

i know for a fact that u4 pin 4 was a nice square wave when I started, not sure about pin 1 though. The moment I shorted it was when I started getting odd shapes at pin 4.
I?ve decided to order a fresh board and start again with new components, luckily wasn?t too far in, I?ll post back with my findings

[jeanhubert]

Thanks kt315.

Hi Denots,

Here are images from my version.
As I measure the same as you, you think I also burnt some components?

[Denots]

Thanks kt315.

Hi Denots,

Here are images from my version.
As I measure the same as you, you think I also burnt some components?
[ATTACH]47370[/ATTACH]
[ATTACH]47371[/ATTACH]

quite possibly you may have done the same as me, Like you say we have very similar scope results.
The only thing I haven’t replaced yet are the mosfet, capacitors or resistors, oh and the two voltage regulator chips but I have them on order.
Ive had a good probe around and all caps seem to be within range but having trouble testing resistors while fitted to the board, hence the reason I decided it easier to start again. It seems like the right hand side of the board, the power supply is all working just fine, seems to be somewhere on the left hand side, hopefully I can get the new board to the same step and test the old and new boards against each other and hopefully pinpoint what’s going wrong.
by any chance are you using a bench power supply to power your board?

[jeanhubert]

No, I am using a 12v battery.

[Denots]

I see, I only ask cos I’ve killed a total of two different boards now using a bench supply, one mpp and a geotech baracuda, stopped using the power supply now in favour of a 12v battery pack, soon as I did that built my second mpp without a glitch

[waltr]

No, I am using a 12v battery.

I see, I only ask cos I’ve killed a total of two different boards now using a bench supply, one mpp and a geotech baracuda, stopped using the power supply now in favour of a 12v battery pack, soon as I did that built my second mpp without a glitch

I also use a battery but ALWAYS put a current limiter in series.
A 40 Watt automotive tail light limits current to about 3-4 Amps and prevents smoke if you slip with a probe or clip the wrong point.
This has saved me many times.

[jeanhubert]

Hi,

Does anybody else have scope of U4 pin1? Best if the design is working for sure

Anyway, Denots, my understanding of this part isn't 100% sure but, for me C5 charges through R11+R10 until its volatge reaches Vp of 40106, when this level is reached pin 2 of U4 goes to -5V, hence the charge of C5 should now be done using R11 only. What we do see here, is that the voltage goes up and down, I am not sure of the exact reason of that, I mean the up and then the down, but the time it takes, matches the pulse duration we see in the instructions with figure 5, about 100 us. Then when Vn of 40106 is reached we restart the whole process. In addition the frequency of the signal at pin 4 seems correct and the pulse duration too. So maybe it's correct.
What do you think?

[Denots]

Hi,

Does anybody else have scope of U4 pin1? Best if the design is working for sure

Anyway, Denots, my understanding of this part isn't 100% sure but, for me C5 charges through R11+R10 until its volatge reaches Vp of 40106, when this level is reached pin 2 of U4 goes to -5V, hence the charge of C5 should now be done using R11 only. What we do see here, is that the voltage goes up and down, I am not sure of the exact reason of that, I mean the up and then the down, but the time it takes, matches the pulse duration we see in the instructions with figure 5, about 100 us. Then when Vn of 40106 is reached we restart the whole process. In addition the frequency of the signal at pin 4 seems correct and the pulse duration too. So maybe it's correct.
What do you think?

Yeah I know what you mean everything else checks out, getting the right results for all the steps so far but like I mentioned my wave at pin 4 was square to start with now it?s got a slope, it might not matter and possibly it?s from adding parts in the next step? I?m not going any further until I?ve built the next board to this point and seen the results.
Board should be here in the next day or so.

I also use a battery but ALWAYS put a current limiter in series.
A 40 Watt automotive tail light limits current to about 3-4 Amps and prevents smoke if you slip with a probe or clip the wrong point.
This has saved me many times.

wise man, I was a little more foolish and chose to ignore the advice against using dc power supply, lesson learned.

[jeanhubert]

Hi Denots,
Any news, building from scratch, with a New kit?

[Denots]

Hi Denots,
Any news, building from scratch, with a New kit?

Hi, no not yet sorry, been working on coils for the mpp over the last week or so, haven’t got round to doing anything with the baracuda yet.
I have all the parts now to get to where I was except I know I ordered some 79L05 and 78L05, one has turned up the other hasn’t yet, pretty sure I’ve got enough for step one though, might give it a bash tonight

[Denots]

Made a start on the new board,
step 1 - 4.9v
step 2 - all assembled except Voltage regulator at U6 (79L05) ordered 50 for ?1.58 but got to wait for delivery, should be here by 15th Oct though lol, might order one up in the meantime.

Heres some circuit porn for you to keep you going till the next update

[Denots]

Step 4 is now complete, here is a picture of u4 pin 4 on the old board after the short


Here is u4 pin 4 on the new board


u4 pin 1 old board


u4 pin 1 new board

[jeanhubert]

Hi,
so pin 1 are the same right? I mean the captures you uploaded are done using different Time/div, right?
As for pin 4, you are right, it's a nice square! I am just wondering if it stays like that once the sampling part will be completed(step 6). I will wait your update once this is done and if it does I'll try to find out what I burnt on my board.

Thanks for helping!

[Denots]

Hi,
so pin 1 are the same right? I mean the captures you uploaded are done using different Time/div, right?
As for pin 4, you are right, it's a nice square! I am just wondering if it stays like that once the sampling part will be completed(step 6). I will wait your update once this is done and if it does I'll try to find out what I burnt on my board.

Thanks for helping!

Not sure tbh, I just push autocapture on the scope and it sets it all nice for me, I’ve just figured how to get screenshots from it so stick with me and I’ll do a comparison with the same time/div and post back with pictures

[Denots]

I tried to upload the photos but they are too big to upload on here, I?m not messing around resizing so here is a screenshot of my findings, top row is the new board, not much difference between them to be fair