IDX-PRO+VDI

[Davor]

...The vdi that is paired with the idx depends on the analog of the idx.

Mind you, the ADCs that run at any decent speeds are terribly expensive, and only recently you could get your paws on a decent one that won't rip you to the bone after alimony, say ADS8354, 16 bit, 700 kSPS, from TI.
Discrimination is traditionally done in motion mode, not because it is not possible to do in non-motion, but because of 1/f noise and drift that spoil your calculation. The other benefit of motion mode is that you are amplifying the target response without the cyclostationary air signal. So in effect by reverting to motion detection you are considerably improving the dynamic range towards the low target responses, and a simple ADC built in a micro can do.
What you are about to do is pack a full signal span and process everything in a micro. Therefore you need a good ADC with at least 16 bit resolution or better because the targets are found somewhere around LSB. And a bit of luck.

[Koala]

TX is a sinewave and hard to measure with a multi meter.

BOOM... O_o. the sinewave_ easely_to measure by the multimeter, it will show precise due voltage, at AC range,
just cause this is the sinewave. do not agree with you.

Does not work correct with my meter for some reason. Mains measures fine. Detector is 16V peak to peak on an oscilloscope but only 4V or 6V (can't remember which) on my Fluke. Different meters may give different results but that's tested with my working detector several years ago.

[kt315]

TX is a sinewave and hard to measure with a multi meter.

BOOM... O_o. the sinewave_ easely_to measure by the multimeter, it will show precise due voltage, at AC range,
just cause this is the sinewave. do not agree with you.

[Koala]

Daniele3195 Did you manage to fix you detector

TX is a sinewave and hard to measure with a multi meter. Should be some volt on the AC range I can check with mine and a Fluke meter but I know that different meters give different results. Post what you get between outer ground on PCB and TX on AC setting.

From the outer ground on the PCB and RX there should be no full volts on the AC range

[Qiaozhi]

Now I have to get an automatic cat feeder to feed the outdoor cats when I have to travel. So that is my current project.

Somewhat off-topic, but ... why go through all the complications of building one when they're so cheap to buy?

http://www.amazon.com/Best-Sellers-Pet-Supplies-Automatic-Cat-Feeders/zgbs/pet-supplies/2975260011

Then you can spend more time on the more interesting stuff, like the Arduino-based MD.

[scrungy_doolittle]

@scrungy_doolittle, you are extremely lucky not to be my geometry pupil, as I'd flank you with most graceful ease. IDX is a traditional VLF motion metal detector. I explained how such a detector sorts out what targets need to produce a sound, and a mechanism of exclusion. a target between the boundaries will produce a simple sound - nothing more, and nothing less.

However it is quite possible to do exactly the same in a micro, there are constraints that say - don't do it.

With a micro and a display, and perhaps a DAC to make sound indication, the last thing you may wish to do is to revert to a compulsory simplicity of analogue VLF. Because of time-discrete operation, you simply can't produce a stimulus at any desired phase. You just can't. What you can do instead is play with I and Q values, and reach to any degree imaginable by math. That's the detail you flanked.
In analogue you can get to any phase imaginable, but in the very IDX you don't do that. Instead you apply addition to reach a desired discrimination angle, just as you'd do with a micro.

Because you can distinguish an exact angle of any target response by observing I and Q ratio, you do not have to pay any attention to a classical detector mode of discrimination. You simply map phase to a desired sound representation, and display indication, The VDI that is paired with IDX does half of that job.

I suggest you to take a piece of paper and draw it. A little trigonometry will help a lot. Once you are able to visualise things that way, you'd be able to convert it into code, but not sooner than that. There are many things you can do to enhance signal detection with a micro, but mimicking a traditional VLF will surely not get you anywhere.

Hope I did not burst any bubbles with this post.

You didn't, and yes you would flunk me with the greatest of ease I understand the I/Q ratio a bit better, but getting the I and Q numbers to start with without using analog (the goal in my case is a pure digital, just digitizing the transmit and receive signals, and then deriving the rest with the micro) means computing the I and Q if you will. And that, is a miminc of a traditional vlf. Only in software. I've not been on for a while, been very busy dealing with an impending divorce, and work on top of it. Game changer when the wife left. Now I have to get an automatic cat feeder to feed the outdoor cats when I have to travel. So that is my current project. Arduino based, using a RTC and motor drivers. Got all the pieces now, so trying to get the motor part running... canibalized some old copiers and printers for motors. Should be easy with the .99 motor driver boards off ebay, but no joy at the moment. Haven't swung a loop for much time either. Used to be a daily thing. Now, no time to speak of. Did get to coin shoot for an hour or two in Dallas on a business trip. Love my old Whites 5900 di pro, but really want a deeper machine that is computerized.
The vdi that is paired with the idx depends on the analog of the idx.

[gtdavid]

Hello All,
I am building my second idx and I am going to build my own vdi could some one please post the conections pic please.?
Also is the a pic of the cirucit board blocked out into sections as I want to have the micro controll the audio also..
and does any one have info on the blackmax coil I see on some of these?
Any help would be great..

[Daniele3195]

I explained bad excuse. I used a transistor BC517 rotated 180 degrees instead a transistor mpsa13

[Koala]

the transistor is turned 180 degrees because I used a MPSA.

Q4 sound driver should be a MPSA13 ???

[Daniele3195]

the transistor is turned 180 degrees because I used a MPSA. the coil has been connected according to the scheme found in this discussion.







if someone has a pcb working to sell contact me to ask for or the email. thanks again to all who help me.

[Daniele3195]

help me please

Hello everyone. Sorry for the inconvenience. Ineed your help. I am a student with a passion for metal detector and I wantedto combine passion and my study and I wanted to build a metal detector to takethe exams. I purchased two pcb from silverdog last summer and I have assembledbut not working. use my pcb with a coil original Blue Max 950 . I do not havemany tools (I don’t have an oscilloscope) to find my mistake for this reason Iask your help .
It turns the metal detector and leaves only aslight buzz and never varies even if you press any button or potentiometer. Imeasure with meter a supply voltage of about 7 volts on all electronicintegrated. on both strands of the winding coil tx I measure about 4 volts andalso on the edge of the gnd I measure 4 volts. on rx there is tension.

I put some pictures of my work. We acceptcriticism and advice on how to make it work.

if someone has a pcb assembly (used as evidenceor that no longer uses) I am grateful to him for giving me life (of course Ipay the pcb and shipping costs).

I will not steal or copy the project but onlyto be able to combine passion and study. Thanks to all in advance.

image url :

[mohandes]

thanx all.very useful .
how we measure dB in this vlf? for example important this range?
caps in series for reject dc voltage?
regards

[Koala]

this is my analysis fo this pics:
[ATTACH]32853[/ATTACH]
when TX coil send waves to targets and find any metal , so this part protect the TX or i am mistake ?so better say if we delete this part how tx work

Parts in untitled.png are parts of the TX oscillator circuit and works similar to this

You can change the frequency by a small amount by changing the capacitor across the TX winding

I would not go too far but I believe it been altered from 6.5Hz to 12Hz without too much trouble before

[mohandes]

Newbie question .

this is my analysis fo this pics:

when TX coil send waves to targets and find any metal , so this part protect the TX or i am mistake ?so better say if we delete this part how tx work

[Davor]

In VLF we use synchronous demodulators to extract information that is amplitude and phase modulated into the carrier signal (at above 5kHz). This information is directly linked to the speed of targets passing against the coil. So imagine 100 coins in a row, and you pass above them with a coil in 1/4 of a second, you'll notice all 100 of them as 400Hz signal.
For practical purposes we limit the response to ~30Hz because it has better S/N. In case you need sharper response, and you don't need superior S/N, you can filter at 100Hz, or even more.