Delta Pulse

[Geo]

Hi all,
Can I use MC14538 instead of CD4538?

Yes . Yesterday i finished a Delta Pulse for a friend and it works perfect with MC14538 that shop sold to me.

[Max]

Yes . Yesterday i finished a Delta Pulse for a friend and it works perfect with MC14538 that shop sold to me.

Hi Geo,
nice to ear it works perfect ! It's really valuable machine... I know!
Of course it works too with mc14538... they are just Motorola kind of cd4538! (or ONSEMI version)
Also sometimes these are even more stable
Try also mc14066 and let me know... I've noticed really smooth operations with that stuff in sockets.
Buy with confidence.

Best regards,
Max

[1843]

For 2x2m coil it is better to try 9 turns with wire 1.5...2.5mm

Hi Geo,
With 1.5mm wire, the coil totally resistance(with cable) become 1ohm. So the MOSFET burns! DP doesn,t work with coils less than 2ohms.
Regards

[Geo]

Hi Geo,
With 1.5mm wire, the coil totally resistance(with cable) become 1ohm. So the MOSFET burns! DP doesn,t work with coils less than 2ohms.
Regards

Hi 1843. Total resistor must be at least 3...4 Ohm so you must connect in series a resistor 2...3 Ohm/1w. Large coil needs bigger current to create a larger magnetic field. For example Mikron says that Delta Pulse needs 110ma with disk coils and 180ma with square coil 1x1 m.
Regards

[Geo]

Hi Geo,
nice to ear it works perfect ! It's really valuable machine... I know!
Of course it works too with mc14538... they are just Motorola kind of cd4538! (or ONSEMI version)
Also sometimes these are even more stable
Try also mc14066 and let me know... I've noticed really smooth operations with that stuff in sockets.
Buy with confidence.

Best 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

[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

[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

[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

[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.

[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

[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

[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]

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.

[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

[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...