Rev D Build #2 Started

[homefire]

At this point what is your Sample Delay ?

[geoscash1]

Hi Homefire,

After messing around with it for quite sometime the other night, I reset the minimum sample delay from the build doc spec of 22us to 8us so now the adjustability
of the front panel delay pot gives me minimum 8us to 30us respectively. At the lowest setting (8us) it chatters like a bad dog in my garage but its more or less due to the
EMI and the coil I am using for the build.

It actually adjusted down to 4us but it seemed to lose all sensitivity so it must be the coil I would guess along with other standard parts on the board. It does seem to like being set between 10 and 12us and that is where I am getting the best sensitivity right now with the coil being used. I get no heating to any of the Ic's or mosfet no matter where it is set.

I will be doing a couple of the mods that KRinAZ has done on his thread since my goal with any of these projects is going to be used 99% of the time for gold/nugget hunting as I live in gold country of northern cali.

One thing I need to find out is how he did the trimmers to R7, R8 and R33 (not sure of resistor numbers off hand , don't have the mods printed yet) since there are 3 legs to the trimmers but only "2 holes for the resistors", I have to assume the middle leg of the trimmer is jumpered to one or the other leg of the trimmer but I do not know for sure.

This weekend will be doing some of the mods and building a new lexan form for the spider/basket coil and winding it with 250/46 litz and then doing more testing.

[Qiaozhi]

One thing I need to find out is how he did the trimmers to R7, R8 and R33 (not sure of resistor numbers off hand , don't have the mods printed yet) since there are 3 legs to the trimmers but only "2 holes for the resistors", I have to assume the middle leg of the trimmer is jumpered to one or the other leg of the trimmer but I do not know for sure.

Connect the outer legs of the trimmer to the resistor holes, and (as you said) connect the middle pin to one of the outer legs. Depending on which leg you attach it to, the resistance will either increase or decrease as you adjust the screw in a particular direction. You'll have to experiment with that.

[Qiaozhi]

I have added you to the Completed Projects list.

[homefire]

Good Stuff. I would use a machine like that here in New Mexico.

[geoscash1]

Added Some of KRinAZ's mods

Well I got to work on the board a bit today and added most all mods, only one's I haven't changed yet is R10 (wont fit so will need to add some
wire or something to get the trimmer installed) and still need to do the audio/threshold mod as well.

Now have the SAT front panel pot, sensitivity front panel pot, added trimmers to R7, R8 and R11. Also swapped the 5532 for the LM4562 but it seemed less sensitive so I switched back to the 5532.

Used KRinAZ's pdf template and made the 8"x10" spider coil form today as well and ended up winding it with some 600v PTFE Teflon coated 7/32 - 24awg, final was 309uH, had over wrapped by a bunch and ended up removing quite a few wraps but it is right about where I want it now.

I reset most of the timing according to KRinAZ's specs except for the 5000 pps, for whatever reason the 50k trimmer topped out and the pps is right at 2400pps.

With the new mods and the new coil the test depths improved quite a bit though without fine tuning it other than resetting the sample delay to 8us.

Air test before mods (using a 7" round magnet wire bundle coil at 329uH)
US Quarter - 7"
US Nickel - 9"
14k gold wedding ring - 7"

Current air test with new mods and new 8x10 ptfe 24awg coil:
US Quarter - 7.5"
US Nickel - 11"
14k gold wedding ring - 9"

I still am not able to detect a 15 grain nugget (it's probably closer to 5 to 7gr as it is laced heavily with quartz) but will keep messing around with settings until it does though.

Will add the other mods when I have a chance and continue to play with the settings. I'm also building another coil form as well but it will be 7-3/4" round and using the 250/44 litz wire for comparison.

Some pics with the board mods and the new coil.






Have a great day,
Geo

p.s. Thanks again to Qiaozhi for the project, Chet for the scope help, WM6 for the heads up, kt315, homefire and godigit for the compliments and for adding it to the completed builds thread...

[godigit1]

Hey Geo,
I've had good luck with the max 412 in place of the 5532 and the lcm 7555 in place of the ne555.
I know the stock mini pulse is only supposed to be capable of sampling at 10 us but unless I'm reading my scope wrong (new scope)I'm sampling down to 5 us.
I've not packaged my basket coil yet, so I'm using a TDI 12 " dual field, its a great fit for the mini pulse. Both the tx and rx have separate shielding ,it hits items a small as staples on the beach and will get a nickle at 12" pretty good. Also for headphones the Garret AT water proof are pretty good. They have a volume limiter so not to blow your head off on large items while still being very clear on small targets. They are about 85 bucks and come with a cover cap that can be used for mounting making the connection waterproof if you plan on a wader unit.
Looking Good!

[geoscash1]

Mods completed but issues arise

Thanks for the info godigit, I have some 7555's and 412's so I'll try them out.

I have finished all mods to the board that were listed in KRinAZ's mod list.

Now I have a couple issues. The detector still works fine but the audio is constant high tone and lacks sensitivity. The original audio/threshold pot was 220k linear, I used a 250k which worked as well and I could adjust to a slow, low growl. With KR's mods, I did not have a 133k resistor so I used a 150k on high side and 82k on low side with a 5k pot, it totals close to original spec 150+82+5=237k (original 222k) . Now, the tone is continuous (cannot slow it down to growl or slow clicks) and sounds similar to a minelab, whereas a constant mild soft high tone threshold no matter where pot is set and with a target over the coil it will raise the pitch and volume. Its not bad but I like to slow the threshold so want to know if I did this mod wrong or if that is how it is supposed to be.

Also, I swapped the resistors at R7, 8, 10 and 11 for trimmers, the only one's I could not find close was the recommended 3k3 @ R7 so I used a 5k, and 33k trimmer @ R10. I set them to mid point and retested and adjusted accordingly.

From KRinAZ mods list:
1) "TX freq at 5000 pps via 50k trimmer pot (which replaced R8 [from the project spec of 1000 pps])" = Could not adjust to 5000pps, only 1700pps maxed on 50k trimmer.

2) "TX pulse width (main sample pulse width?) at 30uS via 3K3 trimmer pot (which replaced R7) (from the project spec of 56uS)" = 5k trimmer, set tx pulse width to 30us. (TP7)

3) "Sample pulse width (secondary sample pulse width?) at 22uS via 50k trimmer pot (which replaced R11) (from the project spec of 48uS)" = Set to 22us (TP eight)

4) "EFE (secondary) delay at 140uS via 33k trimmer pot (which replaced R10) (from the project spec of 160uS)" = Used 50k trimmer set to mid range then adjusted EFE to 142us (134us+8us=142us) TP6

5) "Primary (main sample delay?) sample delay adjusted to minimum of 6uS (from the project spec of 22uS)" = Set to 8us @R6 (TP5)


From minipulse build doc:
Main sample delay = 22us (TP5)
Secondary sample delay (EFE) = 100us + main sample delay 22 = 122us (TP6)
Main sample pulse width = 58us (TP7)
Secondary sample pulse width = 58us (TP eight)

Wording is different between the build doc and mod list so I may have something screwed up as far as adjusting at the correct test point.

After all is said and done I hope some one can clarify this, looking at the flyback with the sample on the scope, it looks wrong compared to what I have seen and read elsewhere (see pic attached). The sample should be close to or be near touching the flybacks rising edge to get short TC or sensitivity to small targets/gold shouldn't it ???

Incorrect ?

Correction in blue

[Chet]

Hi Geo


The Blue trace that you want to display and move to the right is available at TP7. It can be moved right or left by adjusting the pulse width of TP5 which is the pulse that you are displaying. Reference figure 10 of the build document.


Have a good day,
Chet

[godigit1]

Hi Geo,
I have the same first sample location on both my and a friends minipulse. I ask the question is this right and Qiaozhi said basically. Have you been able to adjust the sample to look right?
I seem to be operating pretty well out in the field but was really unsure of the first sample as well.
http://www.geotech1.com/forums/attac...0&d=1437616049
Best
digit

[Qiaozhi]

Hi Geo,
I have the same first sample location on both my and a friends minipulse. I ask the question is this right and Qiaozhi said basically. Have you been able to adjust the sample to look right?
I seem to be operating pretty well out in the field but was really unsure of the first sample as well.
http://www.geotech1.com/forums/attac...0&d=1437616049
Best
digit

TP1 is the TX pulse width.
TP7 is the actual main sample.
TP5 is the main sample delay pulse, which I think you're displaying in your scope image.

Look at Fig. 10 on page 15 of the Build Document.

[geoscash1]

godigit, I tried to move the pulse shape to the right of the rising edge but it does not move, only able to adjust its width, as well as the delay and main pulse so not sure if there is another place to R&R a resistor to make this adjustment.

I have the build doc at my bench with me while working and have adjusted accordingly to what it says on page 15 and used figure 10 for visual help but with these new mods the board is now not working correctly in my mind. It does work and detects fine but the sensitivity is no where near what it was prior to the mods and the audio cannot be correct at all (fast high tone with no adjustment).


I am going to reduce the resistors from the mods that surround the audio/threshold to see if that fixes my audio issue (currently 150k high/82k low/5k pot). Everything else seems to be ok except for the frequency, unable to adjust it to 5000pps (1700 with trimmer maxed) with a 50k trimmer at R8.

My front panel delay adjusts from 8us to approx. 30us but when adjusted to lowest setting of 8us it seems to sample before the rising edge of the flyback based on what the scope is showing me (That's channel 1 @ TP3 and channel 2 @ TP5) which I believe is not right, was always under the impression that the sample should be just touching the right edge for best sensitivity to small items and small gold. I could be and very well maybe wrong though..

Anyway, I'll keep playing with it when I have time to see what I can do with it, if worse comes to worse, I'll just remove the mods and put it back to build doc spec.

Thanks for the replies,
Geo

[godigit1]

Hi Qiaozhi,
Indeed you are right. That is Tp 5, I kept looking at the graph but as one of my lady friends says I man looked it. I kept missing that tp 5 was only shown by spacing only.
Thanks for your patience and expertise with this great project.

[godigit1]

Hi Geo,
I was looking at the graph wrong I kept thinking tp7 was tp5. It took me a while but I finally got it.
So tp7 is our actual sample.
But I am still unsure of actual sample speed. Do we add the delay of the pre amp to tp5 or is that our actual sample time?
The reason I ask is it seems I should not be able to sample as low as I am without mods?
My delay adjusts from 4.6 to 30 us, the only changes I have made are the 555 and the 5532 as mentioned before and I had a large stock of resistors so I chose exact values or just lower, nothing higher than specs.
Here is a picture of tp7 next to the flyback.



I'm still on the road so I cant play with the mods yet but when I get home pulse rate is first thing.
Thanks again for all your help and experimentation with the mods.
Best of luck!
Digit

[KRinAZ]

... and the audio cannot be correct at all (fast high tone with no adjustment).I am going to reduce the resistors from the mods that surround the audio/threshold to see if that fixes my audio issue (currently 150k high/82k low/5k pot)...

Hi Geo, on the Threshold, I ran into this symptom when I was experimenting - it was because the resistances were out of whack. I would suggest this: first put the original (appx 200K) pot back in & verify you can get audio control back, then measure the pot resistances at the barely clicking audio and the resistances at the fastest growl you desire. This will give you the window that you place the pot in. I found I got bad results when the total series resistance was under 200k and a little higher (e.g. 220k) was fine - so used that to find the resistance values for either side of the pot - and I had to try several combinations before I got my adjustment range where I wanted it (slow clicking to distinct loud fast growl). Remember you can use trimmers on either side of the pot and/or make resistor networks (series & parallel resistor combos) to get the resistances just right. I had to be careful to not let the total series resistance not drop below 200K.Hope that helps - Kyle