IDX-PRO+VDI

[onuba]

Shield not working properly. Without a working shield the faintest touch will sound. Coil will be unusable outside.

how to fix the problem. . koala thanks

[der_fisherman]

How to check resistor wattage - very cheap (and very easy) method(s)!!

1/8 is fine. If I remember correctly less than 40ma draw

A VERY cheap and VERY cheerful way to test if the wattage is acceptable is to simply assume that ALL the current goes through ALL resistors (which it doesn't of course!). Then measure the voltage across across the resistor (measure on AC & DC and take the greater value for safety). Multiply the voltage measured by the 40ma (total current consumption) and see if it exceeds the wattage of the resistor type.....it usually will not!!

Or do as many do, is to use the smaller resistor, set everything up and go around with a temperature sensor (index finger!!) and replace the ones that get warm/hot!!!!

This really doesn't replace the proper methods of calculation though!!

A further point is that any resistor above (in this case, assuming say max 12 volts and max 40ma) around say 1k Ohms, will not run hot.....so anything in the range of K Ohms or higher, will be usually safe to use as 1/8th Watt..

This rule may not be followed where large voltages might be developed, in spite of a relatively low supply voltage without checking.....popping one end of a resistor off and placing a current meter in series will bring accuracy to the situation.....

I hope this helps your further if you simply want to be sure....

Regards

Andy

[Qiaozhi]

For hobbyist and experimental purposes, it's easier to only use 1% 600mW metal film resistors everywhere, except (of course) where a higher wattage is required. This greatly reduces the number of resistors you need to keep in stock. If you're planning to get into high volume manufacturing in a competitive market, where price is a major factor, then it makes sense to size every component appropriately to reduce cost. But for the hobbyist there is little point.

[Koala]

how to fix the problem. . koala thanks

Don't ask me I have never been 100% successful at shielding.

My factory coil is 100% good no false signals

This uses two pieces of card covered a graphite/conductive coating.

my attempts are fairly good but still give false signal in the field

One thing I can tell you is the pound shop spaceblanket sold here UK wrapped around the coil does not work in my tests. In fact it's worse than not having a shield never found out what i have done wrong. Think it acts as some kind of capacitor.

[scrungy_doolittle]

Decided to test my vdi out, and hooked power up backward. 2950 got hot, nothing came on. 16 volt ps. 2950 can take up to 43 v.
Does anyone know if that screwup would have killed the PIC or display? (this is a geotech vdi from silverdog.) Going to go get a new reg today, and may replace the opamp just for general principles, but it is the pic and display that worry me.

[der_fisherman]

How to test a new PCB when first using power.

Decided to test my vdi out, and hooked power up backward. 2950 got hot, nothing came on. 16 volt ps. 2950 can take up to 43 v.
Does anyone know if that screwup would have killed the PIC or display? (this is a geotech vdi from silverdog.) Going to go get a new reg today, and may replace the opamp just for general principles, but it is the pic and display that worry me.

For testing, its always a good idea to add a Diode and a low value resistor ( 10 ohms is usually OK.) to one of the power leads.....I always put it in the + lead, but either are fine. Naturally correctly orientated Diode to only allow correct direction of voltage. At least remove the resistor before using fully.
Some leave the diode in circuit just in case the battery gets wrongly orientated for a second or two and the on switch is at ON!
You lose about 0.6 volt with a silicon diode, not enough to worry about. There are better diodes that drop less....
The first switch on should be done with ALL chips removed (assuming that you used sockets!) and then check for correct voltage and polarity at each and every chip socket.....
Best of luck next time.....
regards
Andy
PS You are not the first, or the last to do this!!!

[golfnut]

Tonights Testing,

I found I get higher Range, if I shift off the Null Value slightly inward - probably bending coils added Inductance.

I hooked the X and Y to the Oscilliscope with Gnd of course.
The Angles I got from Y/X based Oscillator Mode - from Flat Left as 0deg - to flat Right 180deg :

* 50 Euro Cent - 10deg
* FOIL - 20deg
* Copper Penny - 45deg
* 2 Euro - bent leg 90deg to 180deg (2 metals)
* 10 cent Euro - 140deg
* 1/8in x 2in Threaded Iron Wire - 145deg
* 3in Ferrite - 145deg
* 5 cent / 2 cent euro - 150deg (Iron ?)
* Beer cap - 150deg
* Quarter - 150deg
* Merc Dime Silver - 160 deg
* 50 cent Euro - 170deg

dependig on how u connect the x and y then vanilla xy mode should look like this from memory

[calebsone]

i just like things to function right and look right i think not jamming a resistor that is longer than the 5cm space between the holes looks better. i had the smaller ones on hand and kinda had no use for them. your right tho trying to buy everything for each project and not just making things work would be to expensive for it to be a hobby... right?

[der_fisherman]

i just like things to function right and look right i think not jamming a resistor that is longer than the 5cm space between the holes looks better. i had the smaller ones on hand and kinda had no use for them. your right tho trying to buy everything for each project and not just making things work would be to expensive for it to be a hobby... right?

In my experience, such "short" places for resistors are probably designed to allow "standing-up" of any "long" resistor. That is vertical relative to the plane of the PCB.

Does anyone else have any other ideas on this?

regards

Andy

[calebsone]

i mean to say the hole to hole space is only 5 mm not cm but if you look at the 100k by the pin point its for a stand up resistor the silk screen is different. and you can buy shorter sizes of all through hole parts if iam not mistaken the do35 ect. after the parts description means the size like max min length. i just happened to have short stuff that fit sitting on the board.... and it looks better.

[ampirate]

Problem,

I Null the Coils.
I try adjusting the GEB.
On the Y/X mode oscilliscope, I see:
* Ferrite Rod vary between 10deg to 45deg depending on GEB.
* but all Foil, Bolts, Nickel, Quarter, Silver Dime, Copper Penny are all the same at 135deg.

Why ??

Also, I get a lot better Sensitivity - if I shift (either way) off the Null of 5mA magnitude to about 20mA magnitude,
but I lose the Ferrite to 135deg then also.

[scrungy_doolittle]

For testing, its always a good idea to add a Diode and a low value resistor ( 10 ohms is usually OK.) to one of the power leads.....I always put it in the + lead, but either are fine. Naturally correctly orientated Diode to only allow correct direction of voltage. At least remove the resistor before using fully.
Some leave the diode in circuit just in case the battery gets wrongly orientated for a second or two and the on switch is at ON!
You lose about 0.6 volt with a silicon diode, not enough to worry about. There are better diodes that drop less....
The first switch on should be done with ALL chips removed (assuming that you used sockets!) and then check for correct voltage and polarity at each and every chip socket.....
Best of luck next time.....
regards
Andy
PS You are not the first, or the last to do this!!!

Chuckle. I got a lm7805 in a to-92 case. Installed it. Hooked 5 .5 volts up correctly, and the regulator got hot. Sigh. I could not find the 602 opamp at Tanners, but did get a new blank pic.
So worst case I will have to reburn the pic, and perhaps replace the op amp. And remove the LCD just in case that is the problem. and start over. I got the VDI populated, without the display, and put one on I had recently purchased. Rather frustrating, because I had hoped to hook it up to my 4900di pro. Mary sent me the schematic for that unit, but it still does not list the parts for the unpopulated meter.
I sure wish I could figure out which other unit used that board, so I could get the schematic for it. It is clearly a board that did have a meter, and they just no popped the meter circuit to cut the cost.

[golfnut]

not certain of your terminology?

Dont mix volts and amps !!

I would not do too much XY action at present..


Can you make the detector NOT BEEP on a pass with small chunk of ferrite ??

- If you cant, nothing else will be right either.

[TANCE]

[jlsilicon]

Sorry, tired in the eyes when I posted it...
- 5mV and 20mV

not certain of your terminology?

Dont mix volts and amps !!

I would not do too much XY action at present..


Can you make the detector NOT BEEP on a pass with small chunk of ferrite ??

- If you cant, nothing else will be right either.

> Problem,
>
> I Null the Coils.
> I try adjusting the GEB.
> On the Y/X mode oscilliscope, I see:
> * Ferrite Rod vary between 10deg to 45deg depending on GEB.
> * but all Foil, Bolts, Nickel, Quarter, Silver Dime, Copper Penny are all the same at 135deg.
>
> Why ??
>
> Also, I get a lot better Sensitivity - if I shift (either way) off the Null of 5mA magnitude to about 20mA magnitude,
> but I lose the Ferrite to 135deg then also.