Need help finding alternate parts for a circuit - Page 1
Forum section: electronics / beginners

author: aries1470
author_rank: Regular Contributor
timestamp: August 28, 2015, 01:44:20 pm
content: 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:NTE312orMPF102orNTE457. 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:HEF4538BandCD4538BC. 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 Wire0.4mm Enamelled Copper Winding Wire 28SWGwould 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 tapeand 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 ofcourseReplacing theLT1054withTC962, 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 sayThank you kindly for your replies.p.s. Yes, I am located in Melbourne, Australiap.s.s. For schematics, lookherep.s.s.s. Sorry for typo's and spellingEdit: fixed a typo, and added links for the LT1054 and TC962

author: alsetalokin4017
author_rank: Super Contributor
timestamp: August 28, 2015, 01:51:31 pm
content: Can't see anything at your links without opening an account and logging in.

author: oldway
author_rank: Super Contributor
timestamp: August 28, 2015, 01:52:56 pm
content: Give us your usename and password so we can login on GEOTECH forum and look the schematics...

author: aries1470
author_rank: Regular Contributor
timestamp: August 29, 2015, 06:22:53 am
content: thanks guys,Sorry for that, as it logs me in automatically, but all other links should workas 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:SchematicBoard:MPP REV-D 3D PCB.gifNow everything should be okayAgain, thank you for your assitance in advance.

author: Richard Crowley
author_rank: Super Contributor
timestamp: August 29, 2015, 07:25:05 am
content: 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 LT1054D10 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.

author: aries1470
author_rank: Regular Contributor
timestamp: August 29, 2015, 10:17:13 am
content: Quote from: Richard Crowley on August 29, 2015, 07:25:05 amThank you for your reply Richard and for your time having a look over the circuit an your recommendations. Now to get the

author: Richard Crowley
author_rank: Super Contributor
timestamp: August 29, 2015, 02:28:19 pm
content: QuoteWow, 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.