Building The Ultimate Delta Pulse using KT315 pcb

[tomari]

so is it 820ohm now??? please post latest parts list!!!!
man, i dont know if you mean i can use 680~820 ohm
or if you just made a mistake and posted 820 instead of 680
i see a parts list you posted 2 days ago on an other thread and R5 is 680!!
my english are not great too!!!

[kt315]

I operate by Eric Foster posting time-to-time. hoping this will help.

PI Coil Lesson
Posted by: Eric Foster (---.ipt.aol.com)
Date: March 25, 2000 04:30PM
Hi All,
Below is a repost of an article I did a while back on my Tech forum.
"There are many factors that influence the design of a PI coil. However, let's decide on two starting parameters i.e. 100uS pulse width and 2kHz pulse rate. One very important factor is what the earliest sampling time is required to be, as this does have a major effect on the maximum useable coil inductance. The greater the inductance and the higher the current, the longer it takes to reduce the field to zero and the later the sample delay has to be. If you are designing a detector for beach and shallow water hunting a good minimum sample delay to aim for is 15uS. With the right components in the transmitter circuit you can then use a coil inductance of 300uH. I have found it best to wind the coil with 10/0.1 PVC insulated stranded wire (10 strand, 0.1mm strand diameter) as this minimises eddy currents generated in the wire cross section. For a 10in coil the winding resistance is about 4 ohms and with an additional 4.7 ohm 4W resistor in series (in the drive circuit) gives a coil time constant (L/R) of about 30uS. For a 100uS TX pulse width (3.3 times the coil TC) the current will have reached over 95% of its maximum value at switch off, which is a satisfactory situation.
Another important factor to decide at the outset is the type of battery and the required battery life. At 2kHz the current consumption with the above values will be about 250mA at 12V which really requires the use of 10 C cells as a minimum. You can of course design for less current and smaller batteries by using a shorter TX pulse, a higher inductance coil with higher series resistance but there will be some performance trade off. Some PI detectors, particularly earlier designs, do not use a series resistor in the coil circuit to limit the current. Is this case the pulse current is often limited by the coil inductance i.e. the current is switched off well before it has reached its final value which would be determined by the coil resistance. Alternatively, the pulse repetition rate can be lowered until the current is of an acceptable value. There are disadvantages to both of these techniques:- Inductance limiting results in the magnetic field still changing rapidly in a positive direction at the point of switch off. This can cause some signal loss due to switch on eddy currents cancelling those generated at switch off. In pulse frequency limiting, the response time and noise averaging of the detector may not be as good.
The shunt, or damping, resistor, will be determined by the resonant frequency of the coil plus stray and cable capacitance. Not being able to display formulae yet (hope to soon as scanner arrives on Monday) you could look up in a radio or electronic text book the formula for a critical damping resistor for an LC with a given resonant frequency. Or you could just try it experimentally. Start with 1k ohms and look at the receiver output on a scope. The receiver (again it depends what front end I.C. you use) should recover cleanly with no ringing before the point of sampling. Add more resistors in parallel until this is achieved. You should end up with maybe 500 ohms across the coil as described above. Use a good quality 0.5W metal film as the peak emf at switch off can reach several hundred volts and I have found that smaller wattage carbon film resistors can break down and go noisy. I have tried a cermet preset in series with a fixed resistor to give an easily variable adjustment but again the high voltage can cause burning at the wiper contact and eventual failure.
Eric.

[tomari]

very informative text my friend, i practice DP, you practice patience!!!
if it had th formula it would give me break but i will find it.

to be honest, this DP is for large **** hidden deep. no coins etc.
soil is full of nails, bullets and other little metal **** that make you dig all the time
no nugget search, no coin search

in general the search go in 3 stages:

25cm coil cleans up the small ****
40cm coil cleans up the small **** that is deeper and searches for bigger target
1x1 coil searches the good stuff

[tomari]

kt315, is there a connection for auto/manual in your pcb? and where is it?

also can you explain auto-reset function ? it resets as soon as you start the machine? does reset button work after this?

[kt315]

I did not make connection auto/manual at PCB.
auto-reset is zeroing SAT part at moment of turn on approx 3-4 sec.

it resets as soon as you start the machine? - yes.

does reset button work after this? - yes, certainly. you push RESET button if you are feeling necessity.

[kt315]

[tomari]

hello, very nice mod, i love it!

one last (i hope!) thing

can you write here in this thread the exact (right) start up procedure?
where each potentiometer must be? please take em from left to right

can you put an explanation of each potentiometer use?

i know you have post it again, but its deep in the forum and search machine does not help at all! (shows thread but not page number)

thank you,
Noob but not drunk.

[kt315]

for start procedure I did especial film.

[kt315]

main rules how right to do DP

Instructions How To Make Delta Pulse Working.rar

[tomari]

thanks KT, on your PCB the E point next to c12 is for all shields of the box?
the =E point next to PPS trimer is a test point

right?

[kt315]

thanks KT, on your PCB the E point next to c12 is for all shields of the box?

this is not E, this is GROUND (GND) symbol. I use this point for shielding of board under it.
ie static field influences via way :::: OPERATOR BODY --- HOUSING (plastic) --- THE SHIELD/GUARD --- THE PREAMP AND BOARD


=E is -E. be cause in P-CAD symbol (-) restricted in some cases, could not use (-) and used (=) instead. yes, test point.

[kt315]

first step you do a graphite spray shield layer

[tomari]

yep, i know its ground, but i couldnt find any other symbol in keyboard
i plan to make a shield box somehow, scrape maybe from copper boards, will i connect every shield to this pin?
i remember seeing in schematic front shield, back shield but on board i think there is this pin for both shields. am i right?

so every time i start up DP i have to have these settings:
- DEPTH – min, at left side, counter-clockwise (first delay)
- DISC – min, at left, counter-clockwise (seccond delay)
- GEB – middle (????)
- SENS – middle (????)
- T/HOLD – middle (????)

thank you!

[kt315]

shield layer is ready now

[kt315]

will i connect every shield to this pin?
i remember seeing in schematic front shield, back shield but on board i think there is this pin for both shields. am i right?

use the points how you find this convenient. if point is FRONT so connect it to front panel if metallic. or
if not metallic but you use pots non soldered at pcb - solder all pots one wire and this wire connect to FRONT shield POINT.
same for BACK POINT. how to shield the board look at last pics.

so every time i start up DP i have to have these settings:
- DEPTH – min, at left side, counter-clockwise (first delay) - this means PULSE WIDTH - you set it on minimal width
- DISC – min, at left, counter-clockwise (seccond delay) - FIRST STROBE DELAY - you set it on minimal delay
- GEB – middle (????) - SECOND STROBE DELAY - you set it on middle delay
- SENS – middle (????) - same
- T/HOLD – middle (????) - same

thank you!