Barracuda Legend Kit Problems

[Old cart]

That will work, if you can swing a temp controlled one that is even better. Something like this

http://www.dalco.com/p-11113-stahl-t...W3YaAjxW8P8HAQ

Check for solder bridges around the damping resistor tracks. When they fail they do not usually fails as a short. To test you meter just touch the leads firmly together in the ohms mode. It should read very close to 0 ohms.If is reads like .7 ohms many meters have a Delta (may show as a triangle) button that allows you to take the current reading and make that 0. if it reads much high than .7 the lead may need work. Note that this only matters when you are measuring low resistances but it is a good habit to get into to check it before testing.

[Impulse]

yer that one says it is temp controlled? and i get 0.1 ohm if the leads are pressed together. ok will look at the solder joints for bridges. I have had a look and my meter has the delta function (RELTRI) button.

[Old cart]

yer that one says it is temp controlled? and i get 0.1 ohm if the leads are pressed together. ok will look at the solder joints for bridges. I have had a look and my meter has the delta function (RELTRI) button.

Yes ideally. However if you are not planning on doing more electronics the cheaper model, or something similiar will do.
.1 is great and if you have delta you can use it too.

[6666]

ok i have measured the damping resistor and i get 2.1ohm (AH!!!!) i will replace it once i get a new soldering iron as my last one no longer functions as it should (should be tomorrow)

is this one ok ? https://www.machinemart.co.uk/p/drap...ering-station/

You did unsolder the damping resistor first ?

[Old cart]

You did unsolder the damping resistor first ?

6666 is right- the damping resistor is in parallel with the coil. Resistors in parallel add like this
Parallel resistance 1/ (1/Rcoil+1/Rdamping)
for a 2.1 ohm coil that equals 1/(1/2.1+1/330)=2.08ohms
conclusion you must unsolder to measure it. Note it could also be open and that would cause the waveform you see. it will also measure about the same 2.1 ohms.

[Old cart]

i had one of these

http://www.ebay.co.uk/itm/Plastic-Sh...YAAOSwhkRWeaTj

it worked to get the board going but was junk after that so i started using the buzzer which was better.

What headphones do you suggest guys? as this is ultimately the route i want to take so if i buy some i would like to buy a 'good starter set/high impedance headphone set) which will also help with the barracuda build (difficult to get 'a' single 'best' i know) or just a speaker that you guys used/bought, where did ya get it? (32 ohm).

Maybe something like this
http://www.parts-express.com/visaton...6-ohm--292-540
These are Chinese, you should be able to get them in UK.

[Impulse]

hey old cart i have a new soldering station (temp control) and i have taken off the 330ohm balance resistor off and it is fine?

[Old cart]

hey old cart i have a new soldering station (temp control) and i have taken off the 330ohm balance resistor off and it is fine?

Ok show me the 5534 pin 3 and 6 waveforms again. With and without the resistor installed.

[Impulse]

ok i have resurrected the old board and it has the same issue with a different coil? 11.4v batt volts. i will go back to the board that we have been working on and desolder the 330ohm balance resistor then take 5534 pin 3 and 6

here

[raygdunn]

Barracuda Legend Kit Problems

Hi Impulse

I have a Barracuda PCB freshly purchased and populated. Not sure it's 100% yet, but I attach comparative traces for the effects of the Delay pot. It is actually 20K (marked '203') rather than the expected 25K, but has sufficient movement for my 10" regular wound coil. The pot. is I think a 20 turn, so very fine adjustment. Rotate it clockwise to reduce the resistance and the delay. (It starts clicking when it reaches the minimum, but I failed to note that at maximum).

The following monitor traces are:
Yellow (main sample): 40106 pin 2;
Green (coil pulse): NE5534 pin 6.
I think I used 9V power supply (rather than 12V). The relative vertical position of the traces as not significant, being the most convenient to fit both on the screen.

The Delay moves the primary sample (main green pulse), with the aim to span the tailing off of the decaying negative pulse.

With delay at maximum, the pulse is probably too late:

(There are a couple of additional small voltage spurious pulses, when the coil is switched on and off.)

With delay near the required point:


With delay near minimum:


With the delay near minimum the pulse disappears. (and Old cart is saying this is a dangerous setting) My thought was, is there any chance that you have the delay near this clockwise limit and so are losing the pulse? 10 turns anti-clockwise from clicking point seems a good initial setting.

It looks like the sample pulse height is 4V, which hopefully addresses Old cart's query.

Other figures: The circuit current with no coil attached is around 27ma. With coil attached, it varies by supply voltage and coil resistance and I have figures from 100ma to 200ma. At 200ma both VT1 and the large coil resistor get hot and I've attached a small heat sink to VT1.

I hope this makes sense and is a helpful contribution. My first attempt at attachments on this forum. I just hope they work OK!

Ray

[Old cart]

ok i have resurrected the old board and it has the same issue with a different coil? 11.4v batt volts. i will go back to the board that we have been working on and desolder the 330ohm balance resistor then take 5534 pin 3 and 6

here
[ATTACH]35392[/ATTACH]
[ATTACH]35393[/ATTACH]

First one with damping resistor is good. This is what you want! The second pic, without resistor rings like a door bell, as expected without a resistor. THIS IS WHAT AN UNDAMPED COIL LOOKS LIKE.
Do you know that coil inductance? If you do if you take another shot at 10uS per division trigger on the neg edge of the main pulse we can accurately determine ring frequency and knowing this we can calculate the effective parallel capacitance. This will help tell us how good the coil and cable are.

[Old cart]

Hi Impulse

I have a Barracuda PCB freshly purchased and populated. Not sure it's 100% yet, but I attach comparative traces for the effects of the Delay pot. It is actually 20K (marked '203') rather than the expected 25K, but has sufficient movement for my 10" regular wound coil. The pot. is I think a 20 turn, so very fine adjustment. Rotate it clockwise to reduce the resistance and the delay. (It starts clicking when it reaches the minimum, but I failed to note that at maximum).

The following monitor traces are:
Yellow (main sample): 40106 pin 2;
Green (coil pulse): NE5534 pin 6.
I think I used 9V power supply (rather than 12V). The relative vertical position of the traces as not significant, being the most convenient to fit both on the screen.

The Delay moves the primary sample (main green pulse), with the aim to span the tailing off of the decaying negative pulse.

With delay at maximum, the pulse is probably too late:
[ATTACH]35395[/ATTACH]
(There are a couple of additional small voltage spurious pulses, when the coil is switched on and off.)

With delay near the required point:
[ATTACH]35394[/ATTACH]

With delay near minimum:
[ATTACH]35396[/ATTACH]

With the delay near minimum the pulse disappears. (and Old cart is saying this is a dangerous setting) My thought was, is there any chance that you have the delay near this clockwise limit and so are losing the pulse? 10 turns anti-clockwise from clicking point seems a good initial setting.

It looks like the sample pulse height is 4V, which hopefully addresses Old cart's query.

Other figures: The circuit current with no coil attached is around 27ma. With coil attached, it varies by supply voltage and coil resistance and I have figures from 100ma to 200ma. At 200ma both VT1 and the large coil resistor get hot and I've attached a small heat sink to VT1.

I hope this makes sense and is a helpful contribution. My first attempt at attachments on this forum. I just hope they work OK!

Ray

Ray you are correct in all your statements. Those sample pulses look correct and the mid sample position is just about spot on.

Impulse have you been rotating the pot 20 turns, that might be the whole problem? If so thanks Ray for helping us find the problem.
May be best to just rotate it as described above until it clicks then go back ten turns.

If this proves to be the problem I would suggest you both cut that link in series with the delay pot and place a 5 K resistor there so the delay trimmer can be set to any position without creating this no pulse situation with the 40106. btw I do not think this should damage the 40106.

impulse do you have a compact fluorescent light anywhere nearby, note the noise on the flat 0 volt part of the signal, Ray does not have that. Could be external noise or maybe even noise from the scope switching power supply itself.

Ray,is it possible to get a good clear picture of the component side of the board for comparison, thanks?

[Old cart]

With delay at maximum, the pulse is probably too late:

(There are a couple of additional small voltage spurious pulses, when the coil is switched on and off.)

It may be possible to eliminate those spurious pulses by bypassing the supply pins 7 and 14 on the 40106 with a .1uF ceramic or film cap with the leads trimmed as short as possible mounted to the back of the board. Those extra pulses can not help anything.

[Old cart]

Impulse I estimate that your ring frequency in post 204 about ( without damping resistor) is 300000Hz which is way to low. This probably means you have too much cable capacitance. How long is you coax? If it is long than 1 M it is probably too long and this wil have significant effect on how the coil damps. Simple cut it shorter and you wil fix this problem. This wil allow us to adjust the damping and set the sampling much earlier which is good if you looking for gold or other low conductivity items. If you are looking for iron it wil not help!

[raygdunn]

If this proves to be the problem I would suggest you both cut that link in series with the delay pot and place a 5 K resistor there so the delay trimmer can be set to any position without creating this no pulse situation with the 40106. btw I do not think this should damage the 40106.

I've already added a 10K pot. I had a "spider" wound coil (has former with 37 slots inside and out), which was very slow, as in insufficient delay adjustment. With the meter on it, the reading glitched, when I touched a certain area. I can only imagine it to be a scratched insulation short. I'll rewind.

impulse do you have a compact fluorescent light anywhere nearby, note the noise on the flat 0 volt part of the signal, Ray does not have that. Could be external noise or maybe even noise from the scope switching power supply itself.

I do have that interference. :-) It is annoying. I switched off my florescent "CSI style" magnifier/work light before taking the shots. 60Hz mains from the high voltage transformer, I'd guess.

Ray,is it possible to get a good clear picture of the component side of the board for comparison, thanks?

Several photos from assorted angles, not 100% indentifiable but close I hope.







Ray