IDX-PRO+VDI

[Gwil]

Just as I thought. 11.8 x 8.93mm is a lot larger than 5mm square. 5mm square = ceramic.

[ampirate]

Let me correct that :
Red Square 1cm x 6mm x 3mm - 0.1uF

I ordered a bunch of 150nF (0.15uF) np0 caps.
I hope this should solve the drift problems.

[Koala]

Just as I thought. 11.8 x 8.93mm is a lot larger than 5mm square. 5mm square = ceramic.

As I said that's for a 100v look at the size for 25v or 50v I don't need one so can't be bothered to look myself. But I have a 63V from RS and it measures 6.5 x 5

polycarbonate/polyester are the way to go for best stability you can put whatever you want in your build.

A surface mount board there is much less choice so some ceramic might be unavoidable.

If you are building from the silverdog kit it's will work as is.

[der_fisherman]

Thanks - Interesting Article.

But, my Metal Detector Projects seem to have a drifting pitch up or down over the span of 1 or 2 minutes - even with the Polyester caps.

For example, one Oscillator project that I was testing last night:
- Just a 2n3904 , a 10K resistor , and (2) 0.1uf polyester caps (little red squares 1/2cm across - mica I believe).
On my Datascope, it showed a drift from 60khz up to 100khz over about 1 minute time
- until I powered it down for a few minutes to repeat the same results again ... and again.

That could be simple temperature instability.
regards
Andy

[Koala]

Thanks - Interesting Article.

But, my Metal Detector Projects seem to have a drifting pitch up or down over the span of 1 or 2 minutes - even with the Polyester caps.

For example, one Oscillator project that I was testing last night:
- Just a 2n3904 , a 10K resistor , and (2) 0.1uf polyester caps (little red squares 1/2cm across - mica I believe).
On my Datascope, it showed a drift from 60khz up to 100khz over about 1 minute time
- until I powered it down for a few minutes to repeat the same results again ... and again.

Think you need to post what it is you are trying to do. Maybe in a new thread. Even though the colpitts oscillator works very well for our application it is subject to drift. 2n3904 will also very low current. More than about 10 mA and it will heat up and drift.

[jlsilicon]

Think you need to post what it is you are trying to do. Maybe in a new thread. Even though the colpitts oscillator works very well for our application it is subject to drift. 2n3904 will also very low current. More than about 10 mA and it will heat up and drift.

Ok,
What should I replace the 2n3904 then ?

[Koala]

Ok,
What should I replace the 2n3904 then ?

We can only guess what is happening you need to post what you are doing

2N2222 has 3x the current If it's required we have no idea because we don't know what you are doing.

more info here

http://www.sentex.ca/~mec1995/tutori...or7/xtor7.html

[scrungy_doolittle]

did you use a linear taper or audio taper pot. It makes a big difference. Our ears hear sounds on a log scale. an A15 taper (also known as an audio taper is what you probably need)

[jlsilicon]

Currently, I am trying to build and learn Metal Detector Circuits bottom up.
I am a Digital EE practiced, but never could understand analog circuits - beyond theory.
I can never Tweak the Analog circuit to get it to work.
So, I am trying to learn the analog, op-amps, radio - and so metal detector circuits - by hands-on practice and design.

[Koala]

Currently, I am trying to build and learn Metal Detector Circuits bottom up.
I am a Digital EE practiced, but never could understand analog circuits - beyond theory.
I can never Tweak the Analog circuit to get it to work.
So, I am trying to learn the analog, op-amps, radio - and so metal detector circuits - by hands-on practice and design.

Best to start a new thread. Post your circuit with your results. Ask what you need to change to achieve your goals. You get more views than in a dedicated IDX thread

Best of luck

[golfnut]

this is a good place to learn some basics, I would recommend getting a DL of pspice and modeling your oscillator. This way you can see the output without the hassle of a build. As Im sure you know. It is good = that drift seemed extreme on any level, dont think it is the cap drift, gut feel..

[jlsilicon]

Ok, here it is then :

Understanding and Building Metal Detector CIRCUITS - Opamps, Oscillators, Transmitters, Receivers

http://www.geotech1.com/forums/showt...ters-Receivers

[scrungy_doolittle]

The whites 5900 schematic has a good one.
Basically the same as the 6000di

[kycoin]

I have a IDX pro with the Mr bill mods, it has worked without problems for two years but today I turned it on and nothing dead !!
Could anybody advise me where to look for problems.
Voltmeter says 11.2 volts at the board when turned off and 2.3volts when turned on.

thanks in advance

[golfnut]

Did the batteries ever get fitted the wrong way,, if so there may be a protection diode that got smoked and is a short.

other than that sometimes electrolytic caps go short.


Try it with the coil disconnected, if you still get the severe volt drop its not the Transmitter or the coil.