Delta Pulse

[Geo]

I believe that a 1266 is a very good and easy detectorwith better sens and discrimination than Tesoro, so i will give it a try. Now about GS4 as i see it will be a normal project if i will use 2 or 3 pcbs as sandwitch. DP is very good and stable but i want to do it a little better at small objects with small coil so a switch to small or big coil and it is OK
My Regards

[ivconic]

...

I can suggest you only GS4 to make....others forget...Not worth!
But you must have accurate schematic and pcb for GS4. As i heard, those posted here are not accurate!? Not sure, but heard that way....I would like to make GS4 also, but do not want to waste my time with faked schematic and pcb...Maybe you can help?

About DP. Aside other things, only thing which interesting me is fact that fet is very cool with 1.5 ohms coil?????
In the past i have a lot of problems with larger coils under 4 ohms...Fet was very hot than?

Best regards!

[Geo]

Hi All .
First for Max. I work my DP at 100 to 400Hz. 400Hz is better because it has better response (at 100 hz i must move slowly the coil if the signal is low otherway i lose the object). The clocking is the same at 100 or 400 Hz. Yesterday i changed the first delay from 30us to 12us. Results....... very bad depth..... why????? i had not time to check it with oscilloscope. I believe that the problem is the coil (maybe it can't go to low). I want to minimise the max delays time so to can increase the freq to 800.... 1000 Hz for small objects detecting.
Now to Ivica.
How and Where are you. I have long time to write you. Of course i am very busy this time and i didn't made a tesoro GS . What about 1266 ?
Now for DP. What are you mean reject? is the first delay Tr4 or the second delay Tr5. If it is the 1st delay then yes if we play with it we can reject some objects. At my detector i have the best results with the potentiometer about short 30....40us. The sensitivity is about the same, max 30cm for 2 euro or 1/2 euro with coil 25 cm 1000uH. With lower inductance i have a little better results but it needs lower dumper (1k/1W now i have 2k2, 1/4w) and is not so stable.
I forgot .... with delay to 80us you can reject the ceramics.
When i will finish the works (maybe on October) i program to construct Barracuda..... 1266 ........ and GS4. IT IS OK TO SPENT MY TIME ON WINTER.
Best Regards

[Max]

After 10 Delta Pulses i have to admit still dont know
everything about PI's..!?
Nothing to do these days, it is kind a monotonous here,
so i decided to make small coil for DP.
I used datas from Hammerhead project:
20cm diamm. wire 0.45mm 26 windings...
Finally resistance is 1.5 ohms.
Also Faraday cage applied (for the first time) in manner
to check this coil on higher frequencies also.
Since reistance is to low i expected fet to become very hot
in no time. I didnt used serial resistance, just waited to
see what's gonna happen...
And nothing happened???? Detector is working good, fet is
cool ???? After 20 minutes still cool???
Oh, yes, i already put heatsink, but small one, just as
"ornament" cose previously i ran this DP on low frequency
with 4-6 ohms coil resistances, so heatsink was needless
at the time...
Still, fet is cool, heatsink also???
I am confused! Now i do not understand this?
I adjusted all pots here and there, made all combinations
and waited fet to become hot - without success!?

1.5cm bronze coin detects at 25cm distance, very sharp!
1l paint can detects at 80cm sharp and at 1 meter with variations in
audio...
Small iron plyers detecting at 50cm distance....

Not so bad at all, considering size of a coil - just 20cm...

"Reject" pot. now working very noticeable as "Disc" on VLF's, but
oposite;
-When "Reject" low, DP detects all sort of metals same,
-"Reject" on "3" , DP stop detecting Al,Foils,some coins
-"Reject" on "6" , DP detects only iron, but very good!

What is this? Sort of discrimination?
Can anybody check this on other machine, i would like to
see some comparsions...


P.S.
I forgot, freq. is 270Hz with this setup...

Hi ivconic,
"freq. is 270Hz with this setup" ok, what's TX on time ?... it's the other key factor that determines consumption... and Vcc value is another one, and then you must consider inductance/resistance and then calculate the peak current (when your fet switch-off happen) and also average power of one cycle using integral of charge function of inductor...

Another thing that's important to notice if there will be too hot running on fet is its breakdown voltage and ...cause at breakdown, during switch-off, your fet must dissipate energy due to collapse of magnetic field, cause by Lenz law you coil store this energy:

|e| = |L* di/dt|

High breakdown voltage mean that your fet "opens" before of small breakdown devices (e.g. BUZ11)... then the eccess energy goes at ringing dump at dumping resistor (that become sometimes more warm than fet!).
And , of course clamping diode that suffer forward conduction during switch-off.

I had a trouble on XR-71 due to these facts... then have to change BUZ11, cause have it warm too much (freq. 400+ Hz), I've used there with an IRF740 (400 volt breakdown voltage!)... even if so I have more Rds on it remains cool (and now is big dumping resistor that dissipate big fraction of energy)!!!

Best regards,
Max

[ivconic]

!?

Forgot to post photo!?

[ivconic]

???

After 10 Delta Pulses i have to admit still dont know
everything about PI's..!?
Nothing to do these days, it is kind a monotonous here,
so i decided to make small coil for DP.
I used datas from Hammerhead project:
20cm diamm. wire 0.45mm 26 windings...
Finally resistance is 1.5 ohms.
Also Faraday cage applied (for the first time) in manner
to check this coil on higher frequencies also.
Since reistance is to low i expected fet to become very hot
in no time. I didnt used serial resistance, just waited to
see what's gonna happen...
And nothing happened???? Detector is working good, fet is
cool ???? After 20 minutes still cool???
Oh, yes, i already put heatsink, but small one, just as
"ornament" cose previously i ran this DP on low frequency
with 4-6 ohms coil resistances, so heatsink was needless
at the time...
Still, fet is cool, heatsink also???
I am confused! Now i do not understand this?
I adjusted all pots here and there, made all combinations
and waited fet to become hot - without success!?

1.5cm bronze coin detects at 25cm distance, very sharp!
1l paint can detects at 80cm sharp and at 1 meter with variations in
audio...
Small iron plyers detecting at 50cm distance....

Not so bad at all, considering size of a coil - just 20cm...

"Reject" pot. now working very noticeable as "Disc" on VLF's, but
oposite;
-When "Reject" low, DP detects all sort of metals same,
-"Reject" on "3" , DP stop detecting Al,Foils,some coins
-"Reject" on "6" , DP detects only iron, but very good!

What is this? Sort of discrimination?
Can anybody check this on other machine, i would like to
see some comparsions...


P.S.
I forgot, freq. is 270Hz with this setup...

[Max]

With the previous tests i measured the delay (ΤΡ4) of the DP. It is 50usec I dont remember about second delay (TR5). When i will play again with DP i will measure all the times and i"ll give them here.
But if we want to make the Delta Pulse better at small objects i believe that we must make the delay 30usec max.
Your opinion?????
My Regards

Hi Geo,
I've done some different setup on it using 15uS delay. I must admit I get better response on small items with that first delay. I don't use DP often cause have other PIs and play with them e.g. when can search on beach.
I maked same thing on XR-71, that's similar to DP too and works cool... stable... etc but consumes a lot more due to higher frequency.
I use same coil that use with GS4... a very good 8'' round fastmonocoil, that can be used till 8uS delay (but I never set 1st delay under 10us on GS4... too instability for my taste).
I think that if you want experiment with lower delay (that's a useful thing in the 10-15us range) you need having such a coil... I've made following BBSailor article... using mylar stuff (or the scotch mesh tape or also lead-tape if you find some). If you make such a coil you could do everything in that range without worring of coil disturbance on DP operations at lower delay.
My greater problem with PI is on inland sites. I get them working ok in beach and "easy" soil... but get stuck when there are bricks, pottery, fragments of ceramics. Not only: the more the sensitivity (e.g. GS4) the more the false signals due to iron oxides... so I gave up on those for these kind of inland sites and use BandidoII at now (I'm planning to realize GoldenSabre but have few time now) and I'm ok with it... though depth is not like with GS4 or Delta.
I think that good setting for small object with PI are like in Eric Foster's designs, low 1st delay and frequency from 400Hz up. But false signals are big problems for me.

Best regards,
Max

[Geo]

I attach here the file with the clocking of my Delta Pulse. The file is not mine but i changed the times as i measured my DP.

[Geo]

Delta Pulse delay

With the previous tests i measured the delay (ΤΡ4) of the DP. It is 50usec I dont remember about second delay (TR5). When i will play again with DP i will measure all the times and i"ll give them here.
But if we want to make the Delta Pulse better at small objects i believe that we must make the delay 30usec max.
Your opinion?????
My Regards

[Geo]

Perhaps you have the potentiometer connected incorrectly. Try connecting R20 to the other end of the pot.

Hi Qiaozhi . I am sure.... i have connect the potentiometer right at both detectors.

When you lower the Gain pot, you have reduced the noise!!
So you have increased the S/N ratio.
Have fun

Maybe 1843 . Thanks

Hi Max . You say about the same with 1843. MAybe you have right.... but there are other detectors with more... more gain at first stage 1000....10000 without any problem. Also i tried to change the gain of the first gain (2..3 times) with the same results . Before 2 days i experimented with DP about 3 hours. I connected 2 oscilloscopes and i tried to see where is the problem .
I am afraid that the amplifier comes in saturation and thus needs more powerful signal so that it enters in situation of aid.
I dont stop. I will try again and i"ll tell us about.........
My Regards to all of you

[Max]

I attach the very known schematic of Delta Pulse. I want from EE here to see the shematic and tell me about one question.
R20 is in series with a potentiometer 20K to regulate the gain (and the sensitivity of the detector). R20 is connecting to the inverter input of D5A. The gain of D5A(tl062) is R21/(R20+Rgain...potentiometer). So when the potentiometer is at zero resistance we have the maximun gain =R21/R20.
Yes...... BUT ......
Now i have 2 dtectors Delta Pulse that work fine and the maximum sensitivity (and max depth) is when the potentiometer is at full resistance (low gain).
WHY?????
I wait
Regards

Hi,
yes seems strange... your are right about gain, zero res. at pot and you get maximum gain of d5a. But there is not just gain to consider.
As above indicated you must rely on S/N... so I think that lowering gain there mean increasing signal to noise ratio, thus sensitivity.
I think that increasing gain there would amplificate noise in a bigger amount than useful signal. If so...
You know that integration in next stages would mask you noise averaging it... so if increasing gain to maximum mean reducing S/N you'll get less sens cause a same amount of signal is masked out by bigger noise amount and then averaging mask you a part of useful signal that wouldn't be compromised at minimum gain.

Why this could happen ?
Impeadance matching between stages, frequency response alteration of d5a stage related to your operating frequency, noise due to components (Rgain add its own that is proportional to its "used" resistance)... and many others related... like crosstalks in the pcb.
So, it's difficault to find why, what the reason(s) is(are)... but effect you noticed would for sure be related to S/N degradation with increasing gain.
Finding it would mean, maybe, reducing its impact on S/N degradation... with some mod (like I did e.g. in bandido adding gnd plane) thus gaining some depth with increased gain of d5a.
I know from other experiences that most of the times this behaviour depends by PCB design and assembling of boards.

Best regards,
Max

[Qiaozhi]

I attach the very known schematic of Delta Pulse. I want from EE here to see the shematic and tell me about one question.
R20 is in series with a potentiometer 20K to regulate the gain (and the sensitivity of the detector). R20 is connecting to the inverter input of D5A. The gain of D5A(tl062) is R21/(R20+Rgain...potentiometer). So when the potentiometer is at zero resistance we have the maximun gain =R21/R20.
Yes...... BUT ......
Now i have 2 dtectors Delta Pulse that work fine and the maximum sensitivity (and max depth) is when the potentiometer is at full resistance (low gain).
WHY?????
I wait
Regards

Perhaps you have the potentiometer connected incorrectly. Try connecting R20 to the other end of the pot.

[1843]

I attach the very known schematic of Delta Pulse. I want from EE here to see the shematic and tell me about one question.
R20 is in series with a potentiometer 20K to regulate the gain (and the sensitivity of the detector). R20 is connecting to the inverter input of D5A. The gain of D5A(tl062) is R21/(R20+Rgain...potentiometer). So when the potentiometer is at zero resistance we have the maximun gain =R21/R20.
Yes...... BUT ......
Now i have 2 dtectors Delta Pulse that work fine and the maximum sensitivity (and max depth) is when the potentiometer is at full resistance (low gain).
WHY?????
I wait
Regards

Hi Geo,

When you lower the Gain pot, you have reduced the noise!!
So you have increased the S/N ratio.

Have fun,
1843

[Geo]

?????

I attach the very known schematic of Delta Pulse. I want from EE here to see the shematic and tell me about one question.
R20 is in series with a potentiometer 20K to regulate the gain (and the sensitivity of the detector). R20 is connecting to the inverter input of D5A. The gain of D5A(tl062) is R21/(R20+Rgain...potentiometer). So when the potentiometer is at zero resistance we have the maximun gain =R21/R20.
Yes...... BUT ......
Now i have 2 dtectors Delta Pulse that work fine and the maximum sensitivity (and max depth) is when the potentiometer is at full resistance (low gain).
WHY?????
I wait
Regards

[Max]

Hi Max. I wrote this because before time an unregister guy asked if we can replace CD4538 with MC14538. If you look at datasheets you will see that at MC14538 there is at one input a smitt triger (if i remember ok) that there is n't at CD4538.
I have n't MC14066 to try it. Sorry but i stay at a small city with only one shop with electronics components.
My Regards

Hi Geo,
"there is at one input a smitt triger " yes there is at input A, right, of mc14538.
I think that's why it's somehow more reliable than standard cd4538... due to less sensitivity to jitter problems on this input.
Used also in other detectors and always they work really good.

Kind regards,
Max