Delta Pulse

[akademiker]

Need some help again.
This pic shows the output of LF357 at pin 6. I searched all across the board, but couldnt find an explanation of this signal. As far as I know, this shows the signal the coil recieves after turning off, right? The first ramp is the decay of the field, about 2µS after turn off it is at the minimum and then the circuit waits about 80µS till it takes a sample of the signal? I already changed the main frequency to about 900Hz and the delay time to be adjustable from 1,5µS to 65µS and the delay width to 1µS to 10µS, but I still get this long time before the ramp goes up again and i can take a sample. Is this long time in conjunction with the decay-speed and thereby the quality of the coil or is it set somewhere in the circuit. As I read on the internet, I need to take a sample after about 15µS to anything golden.
Btw, is it possible to take the sample on the "ramp" or before the "ramp" or just "ontop" of the ramp?
Sorry if my questions sound stupid, but I couldnt find relevant information on the net or on the board explaining this signal.
I use a 2,3Ohm 469µH 24cm coil.

[kt315]

stupid. really. open Carl's Moreland's HAMMERHEAD article and you will see where you do. look last #15 page. FIG 24 and 25.

[akademiker]

stupid. really. open Carl's Moreland's HAMMERHEAD article and you will see where you do. look last #15 page. FIG 24 and 25.

i have already printed the whole article out and readed it twice before asking this question. Its just not clear when the sampling takes place, is it in FIG 26 15µS after the start of the ramp or is it 15µS after the end of the pulse? Its hard to tell, because there is no timescale.

[kt315]

hmmm... for Delta... with comparatively huge MAIN SAMPLING DELAY... that you ask is not so principally... if you do Hammerhead... with only 10 (minimum) us... and you want particularly repeat Eric Foster legendary 5us MAIN DELAY... it is really worth-while.

[kt315]

I took the timing pix from the article of Carl...

[kt315]

...

[akademiker]

Ohhh...now i see... The flyback signal is just cut. Then my coil seems to be pretty aweful if he has such a long flyback signal and I should decrease the pulse width. Thank you very much kt315, now I finally understand what this means
What should I try to decrease the time, till the flyback drops beyond 0.7V ?

[akademiker]

Found the problem, the coax cable was a piece of crap and tripple the decay time >.<, now with simple wire I find a gold ring 22mm at 25cm and at 20 with fast movement

[takos]

delta pulse help

I have just finished to build the Delta Pulse metal detector and i would like help.
my delta pulse work well only with 12v -12.3v if the voltage is little less or little more dosnot work
i have power supply 0-30v for test
become the same and the battery only 12v work.
please help me if there diagram volt test sorry for my english

[akademiker]

Does your "low battery" led (the red one) turn on when you go over or under 12V ?
If yes, the problem is probably in the battery check circuit, check T10 and VD15 for polarity and scorch marks
Can you measure current comsumption at 12V, 12,3V, more than 12,3V and less than 12V ? Maybe a semiconductor is screwed up.

[takos]

delta pulse help

Thanks for the reply.
no problem at T10 and vd12
If the voltage is more than 10v does not turn led only more less!
current consumption is 100ma to 12v same 12.3v and work well.
current consumption is 95ma,98ma to 11.8v and does not work.
i thing there is not problem whith current
also if changing conditions noise potesiometer the current
consumption changed litle
sorry for my english
thankyou very much
i waiting for help

[vourvon]

DP Project Result

Hi,

Finished assemble Delta Pulse and lastly build the coil 1.1m X 1.1m / #24 awg with total resistance of 6 ohms ( 16 turns ), I get info to Thunting Delta Pulse topic that it must be less than 2.4 ohms the resistance of the coil to not over heat the MFET, so I change into 1m X 1m with total 5.5 ohms ( 16 turns ) and not meet the 2.4 ohms so I reduced into 8 turns and I get 2.7 ohms also not meet but I need to try. The result when I turn on the power it's work with poor detection 30cm metal can detect at 15cm in air test. Then I need to try 16 turns no detection result and found that my battery ( 10 volts ) is low so I used the car battery ( 12.8 volts ) and start checking the result after a minutes the R6 start a little burn and a little smoke then I immediately turn off the unit. Anyone help is highly appriciated. Thank you

1. What parts should be possible damaged and need to change
2. I need 1m X 1m coil, I have available #24 awg, How many turns I need or need to change the # of wire.

vourvon

[nick_f]

Hi,
Finished assemble Delta Pulse and lastly build the coil 1.1m X 1.1m / #24 awg with total resistance of 6 ohms ( 16 turns ), I get info to Thunting Delta Pulse topic that it must be less than 2.4 ohms the resistance of the coil to not over heat the MFET, so I change into 1m X 1m with total 5.5 ohms ( 16 turns ) and not meet the 2.4 ohms so I reduced into 8 turns and I get 2.7 ohms also not meet but I need to try. The result when I turn on the power it's work with poor detection 30cm metal can detect at 15cm in air test. Then I need to try 16 turns no detection result and found that my battery ( 10 volts ) is low so I used the car battery ( 12.8 volts ) and start checking the result after a minutes the R6 start a little burn and a little smoke then I immediately turn off the unit. Anyone help is highly appriciated. Thank you

1. What parts should be possible damaged and need to change
2. I need 1m X 1m coil, I have available #24 awg, How many turns I need or need to change the # of wire.

vourvon

Hi Vourvon,
If the coil has higher resistance, it won't overheat the MOSFET (the current will be lower if the resistance is higher). Are sure that your ohmmeter measures correctly? Maybe you have poor contact on the leads. The fact you reducred the number of turns to 8 and yet you measure a higher resistance than for 16 turns means you have measured the resistance incorrectly or have poor contacts on the leads. If the coil has too few turns, it results in a low sensitivity and also the current provided by MOSFET will be very high and it is likely you can burn the MOSFET transistor (or overheat it).
If you only have AWG #24 (I don't know if that is the right diameter or not), in case you need lower resistance, you wind two strains of wire at the same time (so the total diameter is higher and resistance is lower), respecting the number of turns for the coil.

Regards,
Nicolae

[akademiker]

AWG 24 is about 0,5mm diameter and has 89Ohms per km, so you need about 27m of wire for about 2,4 Ohms, which is 7 Tturns on a 1m X 1m "ramka". According to my calculations your 1m X 1m with 16 Turns should have 5,7Ohm, so your ohmmeter should be pretty right.

The coil design of a PI detector is not as crucial as for example with a IB machine, so you should search for the error inside your circuit. Maybe your wires are hanging loose and collect noise from other parts. I had some problems with my own delta pulse, cause the wires leading to the "sense" pot were close to another op-amp and collected a lot of noise, what decreased sensitivity. Also if you have an osciloscop you should check if you sample the backpulse at a reasonable delay. About 30-100µS if I remember correctly.

[vourvon]

nick_f,

Thanks for the reply. Yes I'm sure to the reading of my VOM ( analog ) bcoz I checked to the other VOM ( digital ) almost read closely, No not measure a high resistance when I reduced the no. of turns from 16 with 5.5 ohms to 8 with 2.7 ohms.

akademiker,

Thanks for the reply, I don't have a osciloscope but in my company have many osciloscope and I can go entered the units but without coil, can I check the signal to osciloscope without coil.

Same question:
1. What parts should be possible damaged and need to change
2. I need 1m X 1m coil, I have available #24 awg, How many turns I need or need to change the # of wire.
Additional.
3. What is the minimum and maximum resistance of the coil.

vourvon