Arado 130

[satdaveuk]

All that was wrong this one was coil plug leads needed resoldering and cleaning of battery compartment due to leaking batterys, very impressive non motion detector.
I find it very touchy to set up, needs to be switched on for a few minutes before tunning but if gain is wound almost full and setting between tunning and meter centre a bit at a time with search coil about a inch off the ground just so you can here the threshold, then you have a non motion detector thats equal second to none out of the machines ive had experience with.
A few pics notice the few components only one ic a few transistors variable capacitor for tunning range, components in search head so i couldnt measure inductance.
Im dead interested in building one of these for a project, only problem i could see would be obtaining the tunning capacitor and coil spec.

[ivconic]

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[goldfinder]

Looks like a great project potential

A simple but very good detector. My kind, love simplicity. We many times makes things too complicated and lose sight of what we are trying to do.

Another possibility is to get the basic circuit down pat and then interface it to a microcontroller. A little programming in a uC with a an A2D could solve any interface problems. And they are only a single chip!

As to variable capacitors - they are out there. Check eBay. Also, You might be able to replace the var cap with some bit of simple circuitry. The wizzards on here like Mr. Q or Ivconic might have some good suggestions in this area.
Goldfinder

[ivconic]

A simple but very good detector. My kind, love simplicity. We many times makes things too complicated and lose sight of what we are trying to do.

Another possibility is to get the basic circuit down pat and then interface it to a microcontroller. A little programming in a uC with a an A2D could solve any interface problems. And they are only a single chip!

As to variable capacitors - they are out there. Check eBay. Also, You might be able to replace the var cap with some bit of simple circuitry. The wizzards on here like Mr. Q or Ivconic might have some good suggestions in this area.
Goldfinder

Yes, actually Arado can be very usable detector even nowdays.
It is real non motion and that's what makes it very interesting even today.
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Yes; that huge var cap is the weakest part in whole arrangement.
Once it "sucks" moisture from the air and get covered with oxide layers - all the troubles begins!
So yes; it would be excellent solution to find a way to somehow electronically replace that var cap.
Sort of electronic variable capacitance circuitry is needed there.
Problem is in it's huge capacitance to be varied - some 500-600pF.
It would be easy to achieve same thing with varicap diodes, but those are mostly limited to 1-30pF range.
Biasing such diode with certain voltage will cause it's capacitance to change in given range.
Yet, as i said, it is not enough wide range to replace mechanical var cap in Arado.
A bit more delicate circuitry is needed there...
Very nice problem to solve!

[ivconic]

Sorry! Actually it is 150pF - not 500-600pF!

[satdaveuk]

If i can stall the customer a few days i will take it apart again and measure the variable capacitor, anyone have any ideas on the inductance etc of the search head it runs at 5.5khz, but as i said there is components in there, also i took the coil plug connections for fucture ref.
Be even better if i could px the unit as he was talking of upgradeing but only wants to spend £150, so to be honest with the man hes better keeping the 130.
Ivonics.... is that the pcb layout of the 130 sitting on your workbench? I ask because it will save me takeing the pcb out for pics, the way my workload stands at the moment im pushed to do anything else and as i said he will be wanting it back soon as its the only one he has.
Im not charging him because he gave me a fisher 1265x which needs a on/off volume control and one of the battery holders is naff, apart from that it seems to work fine.

[ivconic]

I busted my coil long time ago.
Those photos are dating from than.
It was really long time ago and all i saved from than was only this sketch:

[satdaveuk]

Not really much good then, Not worth attempting till we have something more solid far as coil spec plus connections, I been down that road before, time exspense then bin.
If we dont get any luck here will try and weed it out of Arado.

[ivconic]

Yes, at the time i hadn't inductance meter, so i could only measure resistance.
Those components inside the search head are just few resistors and one capacitor.
Those were hard joined into epoxy, so i tried to pull them out and read values but i busted them doing that.....

[satdaveuk]

Yes, at the time i hadn't inductance meter, so i could only measure resistance.
Those components inside the search head are just few resistors and one capacitor.
Those were hard joined into epoxy, so i tried to pull them out and read values but i busted them doing that.....

But you tried them who dares wins you may have pulled it off then it would have been all singing danceing

[Qiaozhi]

A simple but very good detector. My kind, love simplicity. We many times makes things too complicated and lose sight of what we are trying to do.

Another possibility is to get the basic circuit down pat and then interface it to a microcontroller. A little programming in a uC with a an A2D could solve any interface problems. And they are only a single chip!

As to variable capacitors - they are out there. Check eBay. Also, You might be able to replace the var cap with some bit of simple circuitry. The wizzards on here like Mr. Q or Ivconic might have some good suggestions in this area.
Goldfinder

Varicap diodes can only be used in circuits with low signal amplitudes. Therefore, I doubt this solution would work effectively in this design. It would be better to redesign this part to remove any reliance on the variable capacitance. I presume this capacitor is used to balance the coil, and has something to do with discrimination? Is that the intended function of the TUNE control?

[ivconic]

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[satdaveuk]

Varicap diodes can only be used in circuits with low signal amplitudes. Therefore, I doubt this solution would work effectively in this design. It would be better to redesign this part to remove any reliance on the variable capacitance. I presume this capacitor is used to balance the coil, and has something to do with discrimination? Is that the intended function of the TUNE control?

Yes it Qiaozhi and I for one have not got a problem still using that part of the design parts permitting, its down to how well this machine performes why alter it when its dam well works well.
Ive since sent a nice letter to Arado explaining I need the spec of the coil to keep one of my old gents happy who bought from new back in the 80s and wants to keep it going.
Cause the days going to come where we get one of these in with coil problems and dont want to scrap it like ivconics did, although will say his pc looked better for wear compared to the I posted here

[satdaveuk]

Interesting information on coin responce with the 130

[Sean_Goddard]

With a little careful design why not "binary" switch capacitors in parallel? Using 4066's or 4016's you could use two 4 bit up/down counters to cycle through the values. you need to pay VERY special care to parasitic capacitances and screen the whole thing in a metal can most probably, but it would be made to work. I think you were over thinking the problem. Keep It Simple See?