Barracuda Legend Kit Problems

[Old cart]

it seems -E is OK. a digital meter gives wrong value if a voltage is not symmetrical and not sinusoidal, on AC range or DC, no difference.
you have not to take attention on those voltages.

That is correct, it will not be the right voltage if it in not a true RMS meter, but it will be a relative voltage.

As an example, if the FET is on all the time the DC voltage will be close to the supply voltage.

Most cheap meters, when measuring AC, assume a sine wave and then multiply that voltage by .707. They really respond to the peak of the waveform not the true value. True RMS meters measure the heating value of the waveform so are accurate for any waveform within the meters bandwidth.

[Old cart]

Hey everyone thank you for your patience and help i have had another play with the new board and i have managed to get it to pick up a gold ring about 5-6 (good or bad?) away i have ordered some new 0.5mm enamelled wire so i can make a more precise coil. What have you found to be a better design/size for the coil searching for coinage, rings and relics ect? I know this is a question that has loads of answers but im looking for the best place to start as you guys have been using the barracuda in 'real world' situations, would the basic mono coil be best for roughish to smooth beach or some other variation? also whats with the shielding as i have tried with foil but it only made things worse not better which thought i should do?

That may be about right for your coil. Two things MUST be set exactly right to detect low conductivity items like small gold.

1. The coil damping resistor must be optimized so there is no ringing. The coil must NOT be overdamped either. Search these threads for damping or dumping resistor. There is much written on that subject. On my detector changing from the design value to an optimum value increased the depth on gold by 30%. You will need an oscilloscope to do this properly.

2. Once damping is set spot on then the delay control and delay trim must be set for the minimum delay that your detector/coil will support. While this can be done by ear, as I described earlier, using a scope makes it much easier.

The likely reason you did not hear any change when you changed the delay is that your minimum delay can not be set short enough.
on KT315's schematic R10 sets the minimum delay and the delay control sets the gross overall delay. On Silvedog's board there may not be an R10, it may be replaced by a fixed resistor. If it is you may Haverhill the waveform to substitute a pot to determine the minimum setting.
I like to measure the signal with a scope after the first preamp. This is the same place you measure the DC offset. Start by setting the DC value there back to 0 volts. Then with the scope set to 10uS per division trigger on the flyback pulse. This is the signal that is about 10-15uS wide. You should be able to see some small spikes on the waveform where the first sample is being taken. They should be about 45uS apart. You want to set the delay to minimum ( least delay) and R10 so the first spike, which is the beginning of the sampling period, falls right where the waveform starts to come back to 0 volts. You can determine 0 volts by temporarily disconnecting the scope lead or changing the coupling on the scope to Gnd.
You may have to slightly adjust the delay from to get the best depth. I have found that adjusting the offset slightly can improve the depth because it can affect the way the preamp recovers from the extreme overdrive from the transmit pulse.

Minor adjustments can play a large role in getting best depth.

[Old cart]

Impulse this may be hard to do if you are not familiar with test equipment. Do you have an iPhone or iPad so you could do FaceTime? It would make it a lot easier. We could also do this on Skype but it is not nearly as nice.

[kt315]

That is correct, it will not be the right voltage if it in not a true RMS meter, but it will be a relative voltage.

As an example, if the FET is on all the time the DC voltage will be close to the supply voltage.

Most cheap meters, when measuring AC, assume a sine wave and then multiply that voltage by .707. They really respond to the peak of the waveform not the true value. True RMS meters measure the heating value of the waveform so are accurate for any waveform within the meters bandwidth.

my english is bad. sometimes i want write more but could not. indeed you can take parts from the book and upload its for beginners.

[kt315]

upload texts from this book too

[kt315]

As the Director of Electronics Engineering at the Rowland Institute, Win oversees a fully appointed electronics engineering laboratory with a dedicated staff and three instrumentation benches (including one for use by other Institute members), an extensive suite of electronic test and measurement instrumentation, and a substantial inventory of electronic parts, e.g., including about 850 different types of ICs. The Electronics Engineering Lab designs and fabricates most of the critical electronic instrumentation found throughout the Institute.

[Old cart]

T

As the Director of Electronics Engineering at the Rowland Institute, Win oversees a fully appointed electronics engineering laboratory with a dedicated staff and three instrumentation benches (including one for use by other Institute members), an extensive suite of electronic test and measurement instrumentation, and a substantial inventory of electronic parts, e.g., including about 850 different types of ICs. The Electronics Engineering Lab designs and fabricates most of the critical electronic instrumentation found throughout the Institute.

That is a very good book. I gave one to my son, an engineer for Christmas and he loves it. I am also an engineer and flipped through it. It is a great reference without getting too technical.

[Koala]

Koala just for interest what was the offset voltage that gave best results ?

Sorry can't remember. Can't power it on at the moment as I have borrowed a few bits from it.

I followed the instructions here

[Impulse]

hey guys sorry i havent replyed i have had some work issues the whole site i work on is being shutdown . So i have ordered a roll of 0.5mm enamelled copper wire i will build a coil once it gets here and i will buy a scope once i get paid is this one any good?

http://www.ebay.co.uk/itm/ARM-NANO-D...EAAOxy4c5RsZUd

old cart i dont have an iphone or pad i can down load skype (thank you for being so generous as to help me like this!)

im going to build a 10" coil for coinage and wreckage

once i have bult the coil i will take pics and state the resistance then go from there, using the forum calc i get,

0.5mm Dia wire 124mm inner radius and 20 turns - 0.309mH inductance is this about right as i have read that 300 is about right for this board?

[Impulse]

ooooo and i noticed an old thread that a guy was having an issue with the coil moving in free air if i pick up the coil and swing it in free air i get a beep at the end of each swing? what is that about?

[kt315]

That is correct, it will not be the right voltage if it in not a true RMS meter, but it will be a relative voltage.

As an example, if the FET is on all the time the DC voltage will be close to the supply voltage.

Most cheap meters, when measuring AC, assume a sine wave and then multiply that voltage by .707. They really respond to the peak of the waveform not the true value. True RMS meters measure the heating value of the waveform so are accurate for any waveform within the meters bandwidth.

is the sinusoidal signal clearly for you that I mean? i ask you again because I can not imagine how you measure rectangular 50us pulse with 1/600s period with the high accuracy by primitive chinese multimeter.

[kt315]

ooooo and i noticed an old thread that a guy was having an issue with the coil moving in free air if i pick up the coil and swing it in free air i get a beep at the end of each swing? what is that about?

that is Faraday static electricity about. those people did not visit elementary school in their life.

[kt315]

[Impulse]

ok i used a Fluke 87 True RMS meter is this multimeter to basic?

ok so i have this affect as i have no shielding yet

[6666]

Sorry can't remember. Can't power it on at the moment as I have borrowed a few bits from it.

I followed the instructions here

Thanks for the info.