Minipulse Rev D first attempt

[kt315]

[kt315]

[Old cart]

[ATTACH]35776[/ATTACH]

So the chip supplies are -5 and 0 volts. May be best to stick with that.

[Old cart]

I did not make it clear that I agree with Q. I sort of like that name, has a bit of a Bond ring!

[Qiaozhi]

I did not make it clear that I agree with Q. I sort of like that name, has a bit of a Bond ring!

Qiaozhi is a transliteration of "George" from English to Chinese Mandarin romanized form, known as pinyin.
Unless you know some Mandarin, Qiaozhi is difficult to pronounce. I think it was Carl that first shortened it to Q.
Of course, it's also a reminder of some other Qs, such as the Quartermaster from the Bond films, or the omnipotent being Q from Star Trek.
Take your pick.

[Old cart]

Right! Q it is then. It fits! I can barely speak American ( Texas) English, let alone the the Kings English.

[Old cart]

So the plan them is to fix the existing model calling it perhaps Ver2.1 and then maybe do an enhanced version calling it GEOTECH Bara V1?

[Qiaozhi]

So the plan them is to fix the existing model calling it perhaps Ver2.1 and then maybe do an enhanced version calling it GEOTECH Bara V1?

That's about it. I think we should patch up the existing Apberg Rev-2 board, and then create a new Geotech version.

[Impulse]

ok so i have made a simple coil out of my 0.5mm enameled copper wire 24 turns and it reads as 390uh i get a £2 coin at 20cm, this seems a little short? i have borrowed a laptop so i will get the scope installed soon!

[Impulse]

ok so the scope is working well heres a pic of TP1 the pulse width is 46us how can i adjust this to be 58us?

[Old cart]

ok so the scope is working well heres a pic of TP1 the pulse width is 46us how can i adjust this to be 58us?

[ATTACH]35821[/ATTACH]

I don't know Minipulse well. If that is the transmit pulse width I don't think that would make much difference, if any at all. The narrow TX pulse width will reduce sensitivity only to long time constant targets like iron or silver coins. Narrow pulses are better for gold jewelry.
Do you see how the voltage curve is starting to flatten near the end of the pulse? That indicates the coil current is no longer rising so the coil has achieved a steady state mode limited by the coil resistance. This is good.
The general shape of the pulse also looks good.

[Impulse]

I don't know Minipulse well. If that is the transmit pulse width I don't think that would make much difference, if any at all. The narrow TX pulse width will reduce sensitivity only to long time constant targets like iron or silver coins. Narrow pulses are better for gold jewelry.
Do you see how the voltage curve is starting to flatten near the end of the pulse? That indicates the coil current is no longer rising so the coil has achieved a steady state mode limited by the coil resistance. This is good.
The general shape of the pulse also looks good.

hey oldcart yes i see the 'flat' spot on the pulse its good to know that the basic coil i have is doing ok how do i check that there is no ringing? ,

i thought it best to start at the beginning as this is the first thing during the build that i found that is out of 'spec' i cant test my gold ring as i am charging my battery but the board does seem to be slighty better at detecting the gold ring.

[Qiaozhi]

ok so the scope is working well heres a pic of TP1 the pulse width is 46us how can i adjust this to be 58us?

[ATTACH]35821[/ATTACH]

You can adjust the value of R7 (1k2). I expect the difference is due to capacitor tolerance.

[Qiaozhi]

I don't know Minipulse well. If that is the transmit pulse width I don't think that would make much difference, if any at all. The narrow TX pulse width will reduce sensitivity only to long time constant targets like iron or silver coins. Narrow pulses are better for gold jewelry.
Do you see how the voltage curve is starting to flatten near the end of the pulse? That indicates the coil current is no longer rising so the coil has achieved a steady state mode limited by the coil resistance. This is good.
The general shape of the pulse also looks good.

TP1 is the TX oscillator output. You won't see any "flattening out" on this signal.
In order to see the behaviour of the coil current during the TX-on time, you need to put the scope across R3 (3R3).

[Old cart]

TP1 is the TX oscillator output. You won't see any "flattening out" on this signal.
In order to see the behaviour of the coil current during the TX-on time, you need to put the scope across R3 (3R3).

Q of course. My bad. Impulse, try measuring the voltage across R3. Since Voltage across a resistance is proportional to current this will tell you about the current passing in the coil.
To measure the coil ringing you can monitor the output across the coil, except I recall your scope being limited in the voltage it will tolerate, or the output of the preamp. I think this is TP3. What you are looking for is a smooth return to 0 volts of the flyback pulse ( the one immediately following the transmit pulse). Maybe someone has an example of a correctly damped minipulse coil.