Sandbanks

[Mr.Jaick]

https://www.youtube.com/watch?v=eZQyVUTcpM4

I just Love You Man

[Qiaozhi]

by the way i find a good looking speaker wire to use as box to coil connector
here is a pic if you can see it's flexible and feels fancy:
[ATTACH]53234[/ATTACH]
[ATTACH]53235[/ATTACH]

should i use it or keep the faith in RG58 like cables?

You need to use a shielded cable to connect the coil to the control box.

[Mr.Jaick]

You need to use a shielded cable to connect the coil to the control box.

my coil is not shielded so that means i need to use a RG58 cable then connect the core copper to +12v and the stranded shield to end of the coil
or you refer to a double core + shield wire?

[kt315]

we call a wire end running to MOSFET's DRAIN as 'HOT END', a coil wire end to power line 'COLD END' respectively.
so COLD END is shield point connection. ALWAYS. simply understand that and remember.
not so hard to understand.

[Qiaozhi]

my coil is not shielded so that means i need to use a RG58 cable then connect the core copper to +12v and the stranded shield to end of the coil
or you refer to a double core + shield wire?

If your coil is a mono (which it appears to be) then you only need a single-core coax cable. The ground (0V) connection is attached to the outer shield.

[Mr.Jaick]

we call a wire end running to MOSFET's DRAIN as 'HOT END', a coil wire end to power line 'COLD END' respectively.
so COLD END is shield point connection. ALWAYS. simply understand that and remember.
not so hard to understand.

I got it, solid explanation thank you.
so actually we're taking about AC analysis here which the battery becomes a big capacitor and short to ground

[Mr.Jaick]

If your coil is a mono (which it appears to be) then you only need a single-core coax cable. The ground (0V) connection is attached to the outer shield.

thank you very much
in my case it's +VDD which is the same as ground for those pulses i guess

[Mr.Jaick]

can anybody help on this problem?
i made my own PCB for this polones schematic



layout is ok connections are ok but it hardly detects a big iron lock
coil information:
0.75mm enameled
13 turns
1 ohm
should be about 260uh
damping resistor 470 ohms
gain of PreAmp is 3700 (on the high side)

here are all the necessary information of the running circuit
settings are : volt/div= 5v time/div= 2ms otherwise mentioned
1_oscillator output


2_gate of IRF740


3_Drain of IRF740
volt/div = 20V time/div = 2ms


4_drain of IRF740 zoomed out Back EMF
volt/div = 10v time/div = 20us

it has a bit of undershoot on the falling edge about 0.5V

5_cathode of 3,3V zener in front of PreAmp


6_pin 10 of 4011BP


7_pin 6 of preAmp


any help would be great

[Mr.Jaick]

a better view:

[kt315]

2_gate of IRF740
IRF740_gate.jpg
---
how much PULSE WIDTH?

[Mr.Jaick]

2_gate of IRF740
IRF740_gate.jpg
---
how much PULSE WIDTH?

the hole pulse on and off time is 10ms (each division 2ms) = 100Hz
so i think it's about 200us on top(peak) of the pulse and 400us on the bottom side
but over all the duty cycle is 2%

by the way i changed the two gate drive resistors by calculation
the series one to (R6) 27ohms and the pulldown one to (R7) 33K which is ok for the frequency i think.

[kt315]

200us PULSE WIDTH gives 400V p-p. you can not check pulse on the gate because you DO NOT SEE IT.
so also it is HIGHT VOLTAGE and you will burn your o-scope in moment.

[Mr.Jaick]

200us PULSE WIDTH gives 400V p-p. you can not check pulse on the gate because you DO NOT SEE IT.
so also it is HIGHT VOLTAGE and you will burn your o-scope in moment.

i changed the pulldown resistor(R7) on the gate from 33k to 220 ohms and i think it was too low that the mosfet didn't fully turn on(it was dead cold)
I changed that to 2.2k and it's better i guess
now the PULSE WIDTH is 70us or there about and mosfet doesn't get hot at all
detection is improved just tiny bit and i think the problem must be in coil driver and coil itself

do you know what is the optimum gate pulldown resistor for the IRF740 ??
the series resistor for gate(R6) is 27 ohms

now i'll just add couple of turns to the coil see what happens

[surfdetector]

820k under lf357 changed to 1M

Bernte did you put trimmers in place of the two 33k resistors to enable changing the sample delay?

[surfdetector]

can anybody help on this problem?
i made my own PCB for this polones schematic
[ATTACH]53239[/ATTACH]
[ATTACH]53247[/ATTACH]

layout is ok connections are ok but it hardly detects a big iron lock
coil information:
0.75mm enameled
13 turns
1 ohm
should be about 260uh
damping resistor 470 ohms
gain of PreAmp is 3700 (on the high side)

here are all the necessary information of the running circuit
settings are : volt/div= 5v time/div= 2ms otherwise mentioned
1_oscillator output
[ATTACH]53240[/ATTACH]

2_gate of IRF740
[ATTACH]53241[/ATTACH]

3_Drain of IRF740
volt/div = 20V time/div = 2ms
[ATTACH]53242[/ATTACH]

4_drain of IRF740 zoomed out Back EMF
volt/div = 10v time/div = 20us
[ATTACH]53243[/ATTACH]
it has a bit of undershoot on the falling edge about 0.5V

5_cathode of 3,3V zener in front of PreAmp
[ATTACH]53244[/ATTACH]

6_pin 10 of 4011BP
[ATTACH]53245[/ATTACH]

7_pin 6 of preAmp
[ATTACH]53246[/ATTACH]

any help would be great

How did you choose the size of your damping resistor? Did you use the variable damping tool? I am thinking that it is not sized optimally.
Cheers