Step 7 question

[Qiaozhi]

The speaker makes a low tone sound when connected to u4 pin 4 and the coil is 20 turns of .5mm copper wire of around 20cm diameter.

It seems like the TX oscillator must be working. Did you do the headphone test in Step 4?
If Step 4 is ok, then connect a voltmeter to the output of the preamp (U2, pin6). Does this voltage change when you bring a large metal target close to the coil?

[Qiaozhi]

And what answers do you bring to this tread ?

http://www.geotech1.com/forums/showt...rracuda-HELP!!

There don't appear to be any outstanding questions in that thread.

[homefire]

PL2 is the 3-pin connector for the sample delay pot.

Thank You. I have a board and parts in route.

[kosacid]

http://www.geotech1.com/forums/showt...oject-complete

[omr255]

It seems like the TX oscillator must be working. Did you do the headphone test in Step 4?
If Step 4 is ok, then connect a voltmeter to the output of the preamp (U2, pin6). Does this voltage change when you bring a large metal target close to the coil?

The coil constantly makes a very faint sound which the headphones definitely amplified but only when the ear piece was right near the coil wire.
I have checked u2 pin 6 and there is only a very tiny change in the voltage (0.003 volts more) when the metal object is placed in the coil.

Should the inductance be between 0.3 and 0.5 mH ?

I have made another coil this time 14 turns and now the mosfet gets even hotter, almost too hot to touch.

[Qiaozhi]

The coil constantly makes a very faint sound which the headphones definitely amplified but only when the ear piece was right near the coil wire.
I have checked u2 pin 6 and there is only a very tiny change in the voltage (0.003 volts more) when the metal object is placed in the coil.

Should the inductance be between 0.3 and 0.5 mH ?

I have made another coil this time 14 turns and now the mosfet gets even hotter, almost too hot to touch.

Yes, the inductance should be between 300uH and 500uH.
Check the component values around the TX oscillator. The MOSFET should not be getting hot.

[omr255]

Yes, the inductance should be between 300uH and 500uH.
Check the component values around the TX oscillator. The MOSFET should not be getting hot.

Could it be anything specific? I have checked all the resistors on the board and all the values are good. All electrolytic caps are in the right way. All diodes are in the right way.
Could it be the poly caps?
I will take some close up pictures of the poly caps, so they can maybe be compared to a successful build and hopefully that might make it easier to spot a misplaced one.

Left side of board Right side of board
http://imgur.com/glJBCkT http://imgur.com/LGTh8op

[omr255]

Yes, the inductance should be between 300uH and 500uH.
Check the component values around the TX oscillator. The MOSFET should not be getting hot.

Also, forgot to ask.
Does the Wima 6800 red cap have a polarity? I've noticed one of the pins is a but longer than the other.

[chevesne]

At least one mistake. "http://www.geotech1.com/forums/showt...852#post223852"

http://hpics.li/e046f9d

http://hpics.li/1b8c7c1

http://hpics.li/5f0b79e

[omr255]

At least one mistake.

http://hpics.li/e046f9d

http://hpics.li/1b8c7c1

http://hpics.li/5f0b79e

Haha, thank you!

I thought those would get me.

I'll re-solder them into the right spots and post the results.

[kt315]

Also, forgot to ask.
Does the Wima 6800 red cap have a polarity? I've noticed one of the pins is a but longer than the other.

do a pic of this strange capa pls.

[omr255]

At least one mistake. "http://www.geotech1.com/forums/showt...852#post223852"

http://hpics.li/e046f9d

http://hpics.li/1b8c7c1

http://hpics.li/5f0b79e

I have re-soldered the poly caps.
There is a slight increase in voltage on u2 pin 6 but the mosfet still gets very hot.
There is also no voltage on u7 pin 2, could this be caused by the 100k turn-pot being placed around or that has no effect.

http://imgur.com/WvGo11E

[omr255]

do a pic of this strange capa pls.

It's the 1 red one which says WIMA 6800 on it.
I can't take a picture as it is soldered and the pins trimmed.

[Qiaozhi]

C7, C10, C11, C12, C13, C14 and C21 are all the wrong values in your photo.
None of these are polarity sensitive.

Update: OK - I see that you've now changed those in your latest photo.
There must be something else wrong that's not obvious by looking at it. I can assure you that this design works exactly as described, so you must an error somewhere. It's very difficult to debug remotely and without a scope.

[omr255]

C7, C10, C11, C12, C13, C14 and C21 are all the wrong values in your photo.
None of these are polarity sensitive.

Update: OK - I see that you've now changed those in your latest photo.
There must be something else wrong that's not obvious by looking at it. I can assure you that this design works exactly as described, so you must an error somewhere. It's very difficult to debug remotely and without a scope.

The mosfet seem to only get hot when the coil is connected.