Need help finding alternate parts for a circuit

[aries1470]

Hi Guys and Gals  ,

I would like to ask for some help, as I will start assembling soon a metal detector once I receive a PCB.

So I will not be copy & pasting, I will provide a link to my other post on a different forum, since I beleive there will be more people here that would be able to help me quicker and answer me more in depth.
Just remembered, that to view messages, you may need to sign up, not sure, since it auto-logs me in. So I will copy and paste, while providing link/

Please forgive me if I am breaking any ettiquettes etc, as I am still newish here.

Alternative parts for Rev D. Need assistance in sourcing and confirmation.

Hi,
As I am awaiting for the boards to arrive, I wanted to confirm some alternate parts, as I am unable to source, or if I can, I need to purchase a huge quantity.

I will start with the following:

   

• Q4 & Q5: J113. What is their purpuse, and are they critical? I can substitute with the following:
          NTE312 or MPF102 or NTE457. I am leaning towards the MPF102 , then NTE312 (closer to spec's with J113) then NTE457 (due to pricing in that order). Does 50mA actually get used as per the J113 specs? or the whole voltage, since we are running ±5 V. The NTE312, I just flip it around from GSD to DSG so it will be facing the other way, while the MPF102 drops in directly, but is ±25V 10mA.
• Q4 & Q5: J113. What is their purpuse, and are they critical? I can substitute with the following:
          NTE312 or MPF102 or NTE457. I am leaning towards the MPF102 , then NTE312 (closer to spec's with J113) then NTE457 (due to pricing in that order). Does 50mA actually get used as per the J113 specs? or the whole voltage, since we are running ±5 V. The NTE312, I just flip it around from GSD to DSG so it will be facing the other way, while the MPF102 drops in directly, but is ±25V 10mA.
• U6 & U7: MC14538BCP. I can only source the following:
          HEF4538B and CD4538BC. Having looked at the pdf files, can someone confirm if pins: 1&15 are used? Since for the On Semi (Motorola) part, they are Vss and mentions to connect them together, while for all other companies, they are:Pin1: T1A and PIN15: T1B. Else, they are exactly the same part. Can this be confirmed.
• Coil Wire: I will be using Kynar 30AWG Wire Wrap Wire Silver Plated (only because I have it on hand). I have become confused from reading way to many posts. In short, Can it be used without any issues? or is it better to get any of the following wires:
  
  • 0.25mm Enamelled Copper Winding Wire
  • 0.4mm Enamelled Copper Winding Wire 28SWG
  would I need to do anything to the enamelled wire or just use it straight and then shield.
• For coild shielding, would this suffice, will I need shielding? copper tape and will be using Temflex Black Electrical Tape as the insulating material between the spool and the copper tape, would this work if I have understood the assembly isntructions correctly, or I can use kitchen alufoil ofcourse
• Replacing the LT1054 with TC962, I don't see an issue excpet for 20 mA difference in output. I don't see the whole circuit using that much current, but I can be wrong, as I have not worked with coils previously.
• D10: Replace MUR460 with UF3005. This is also 600V but 3A. Is there a reason it needs to be 4A? This is what I have handy.
• R6: 100K Multi Turn. Does it need to be of a certain wattage? or is a 1/8W or ¼W or ½W?
• Why is the IRF740 chosen? Can another part be used? What spec's are we looking at that are needed?

This is for the stock version, once I have it up and running, then I will do mod's, but I want to confirm if these items will be okay.

Sorry for the lots of questions, I just want to have everything ready for when the pcb's arrive, to "hit the road running" as they say

Thank you kindly for your replies.


p.s. Yes, I am located in Melbourne, Australia 
p.s.s. For schematics, look here
p.s.s.s. Sorry for typo's and spelling  [/list]
Edit: fixed a typo, and added links for the LT1054 and TC962

[alsetalokin4017]

Can't see anything at your links without opening an account and logging in.

[oldway]

Give us your usename and password so we can login on GEOTECH forum and look the schematics...

[aries1470]

thanks guys,
Sorry for that, as it logs me in automatically, but all other links should work  as they are not on the website.

I have saved a link of the pdf's:
Assembly Instructions: Building the Minipulse Plus (Rev-D).pdf.
Schematic: Schematic
Board: MPP REV-D 3D PCB.gif

Now everything should be okay 
Again, thank you for your assitance in advance.

[Richard Crowley]

• Question #2 appears to be identical to question #1.  Or did we miss something?
• In Question 1/2 you ask about "Q4 & Q5" as if they were the same thing. I think you mean to be asking about Q3 & Q4 which are the JFET switch transistors.
• NTE469 appears to be the recommended replacement for J113.  Why are you looking at NTE312 which does not seem like a suitable replacement.
• I don't understand you statements about price. The difference in price between NTE312 and NTE 469 appears to be only a few cents.
• My assumption would be that all CMOS 4538 dual one-shots are close enough for this circuit.
• The diameter of the wire will have some effect on the inductance of the coil. But it seems trivial to compensate for slight variations in wire diameter. The outer insulation/plating/whatever will have no practical effect.
• To make little shield boxes, we would typically use scraps of copper-plated PC board material. Or even pieces of tin can folded and soldered together, etc. This isn't critical. As long as it is conductive/metallic (to form a Faraday shield)
• A very brief glance looks like TC962 could be a suitable replacement for LT1054
• D10 doesn't appear to get anywhere near the voltage and current ratings. Probably any diode would work.
• R6 is not dissipating any power. Any variable resistor will work.
• It appears that Q1 is driving the transmit coil, so it needs to be capable of handling the current. The frequency is probably not a limiting factor.

[aries1470]

• Question #2 appears to be identical to question #1.  Or did we miss something?

No, my mistake, when I copied it over and did the re-formatting, I copied twice, 

• In Question 1/2 you ask about "Q4 & Q5" as if they were the same thing. I think you mean to be asking about Q3 & Q4 which are the JFET switch transistors.

A typo, yes, Q3 & Q4, the J113's. You are correct.

• NTE469 appears to be the recommended replacement for J113.  Why are you looking at NTE312 which does not seem like a suitable replacement.

Trying to find an easily accessable J-Fet, without having to go to the "big guys" and they are available somewhere, where it is close to me. I found on the internet a replacement for the MPF102, of which had these as its replacement of which one was the J113, so thought it is a "two way road", if the J113 is a replacement for the MPF102, together with the other ones, then, that could mean it can work either way, but not sure if the circuit would need those specifications, or that they were chosen since they were readily available to the person that was making it, as was the diode D10, due to it being readily available (that was from another post in those forums), so just making sure. Here is the link - Substitute for MPF102 JFET. I hope that clears up my inquiry on why I selected those parts.

• I don't understand you statements about price. The difference in price between NTE312 and NTE 469 appears to be only a few cents.

It is over a dollar difference for me, each , but no NTE 469, only NTE457, MSP102 and NTE312 available to me . The other option, would be the MPF106/2N5485. The other place that I can go to is: Rockby of which carries a large selection, and is same distance as Jaycar from me.

• My assumption would be that all CMOS 4538 dual one-shots are close enough for this circuit.

That is great news 

• The diameter of the wire will have some effect on the inductance of the coil. But it seems trivial to compensate for slight variations in wire diameter. The outer insulation/plating/whatever will have no practical effect.

Cool, one less thing to worry about.

• To make little shield boxes, we would typically use scraps of copper-plated PC board material. Or even pieces of tin can folded and soldered together, etc. This isn't critical. As long as it is conductive/metallic (to form a Faraday shield)

Ok, so some black tape etc, then some alu foil should do for a 1st coil attempt 

• A very brief glance looks like TC962 could be a suitable replacement for LT1054

Excellent, since I have those readily available from another project I had made.

• D10 doesn't appear to get anywhere near the voltage and current ratings. Probably any diode would work.

Thanks, so I will just use the UF3005 I have spare.

• R6 is not dissipating any power. Any variable resistor will work.

This is excellent, since in the future I am planning on swapping it out, and using a digi-pot in its place. Cool, great news.

• It appears that Q1 is driving the transmit coil, so it needs to be capable of handling the current. The frequency is probably not a limiting factor.

Hmm, bugger, as it is an expensive piece for me, buuuuut, I can live with that.
[/list]

Thank you for your reply Richard and for your time having a look over the circuit an your recommendations. Now to get the

[Richard Crowley]

The other place that I can go to is: Rockby of which carries a large selection, and is same distance as Jaycar from me.

Wow, you actually have physical shops where you can buy specific semiconductors in your neighborhood/city?  Most of us have resigned ourselves to ordering everything online.  It is not clear why you think you must use only components that are available locally. Most of us would probably be completely out of luck if we had to do that.