Strange damping on Surf PI 1.2 please help

[antalaz]

Problem solved by re-soldering components ! But I will have problems with lm328... It goes only to 0v or 3.7v
My surf is working at 5khz and 20us pulse width...

I can attach some pics if you want!
I would appreciate your help

I've gave up spiral coil because of the coil shield cap, box i've a loose wound coil with 24awg and delay looks pretty good

[Xtrem]

Replace the 5534, probably its fake, check it using multimeter , between pin2 and pin3 you must measure a diode (0.6v)
i had the same problem with 5532.

[kt315]

Hi everyone !
I'm using an homemade spiral coil.

]

this is strange word SPIRAL. ok. give pics of your coil to seek.

[antalaz]

i've replaced IRF, nothing change...

anybody ?

[antalaz]

I've simulated the NE5534, if R(1M) is disconnected from pin6, i almost get the same issue...

I'll check it out

[antalaz]

I'm back on my surf after a little time being discouraged. I want it to be working !

I've restored my Surf as it was initially, then i've followed Tepco mods which consist of changing values of R1 and R2 in order to modify pulse settings, and make Surf more sensitive to small objects.

Still got trouble, so i've made some measurements, and i think my 5534 is no acting properly... it should amplify my signal, shouldn't it ?
I've got a good signal on the input, but a square wave on pin6

well, i would very appreciate your help.

Pics of scope are attached

i'm also trying to simulate surf on proteus, scheme is finish but the software give me trouble...

thank in advance

[antalaz]

So sad, pin 7 of lm is acting strangely... when i try to set my delay, i've got 0v or 3.8v... no intermediate value...
I'confused, need help please
I think that lm is fried but i'm not sure...

Thank in advance

[antalaz]

I've changed my câble for a 100pF one... looks good ?

[antalaz]

Here is the results... i dont understand why my coil is slowed down... any ideas ?
One pictures is with minimum damping resistor and the other is with max damping resistor (1k)


Please note that i've made those mods:http://prnt.sc/aqfyyk

[antalaz]

just found a piece of coax just long enough. Capacitance of it: 50pF.
I'll try this tomorrow then we'll see changes ! my previous coax was by far more capacitive (i guess "capacitive" is the right word ) ,

[Ferric Toes]

New coil ! Circular, insulated and shielded ![ATTACH]37472[/ATTACH][ATTACH]37472[/ATTACH]

There may be something amiss with the grounding of your preamp as you have a positive tail at the end of the recovery. This can happen if some of the recharge current to the TX reservoir capacitor flows in a part of the RX ground. A good way to avoid this is the ground the RX directly to the ground side of the TX capacitor.

Another cause of this type of overshoot is excessive capacitance in the coil and cable. Try as short a length of cable as possible and see if it improves. You could also increase the value of your damping resistor and see if the overshoot develops into a ringing waveform. If so, it is a coil capacitance problem. Sometimes you can get a faster response by allowing a cycle of positive and negative ringing, as long as the start of the sample pulse is just clear of this.

Eric.

[antalaz]

New coil ! Circular, insulated and shielded !

[antalaz]

I've sandwiched my spiral coil with some insulation material, my delay is now 10uS!

It's working but i think i can enhance it by adjusting delay in a clean environnement.
I'll do it tomorrow.

To be continued

[antalaz]

Yes, i'm thinkin about it

a good spend i guess

[hecbom]

Look into buying "Inside the Metal detector". It explains in detail what you are after.