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What Resistors should I have

Discussion in 'General Electronics Discussion' started by DGPILOT, Apr 8, 2012.

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  1. DGPILOT

    DGPILOT

    2
    0
    Apr 8, 2012
    Hi, i am wondering (as on tuesday, in Australia, im going to stock up on components) :confused:
    What resistors are commonly used, i can only think of about 4, so i'd love to know which value resistors, capacitors, ect i should buy!?
    thanks!
     
  2. davenn

    davenn Moderator

    13,496
    1,830
    Sep 5, 2009
    hi there
    welcome to the forums :)

    4?? try a few more than that :)

    Resistors are so cheap, a few cents each, I would be looking at getting at least 10 or 20 of each value from 1 Ohm to 1megOhm. You will use a good spread of values over the years to come and there will be that weekend when you cant get to Jaycar etc and you need those couple of values to finish a project.
    You could narrow down the values between 1 Ohm and 820Ohm a bit as they wouldnt be used quite so much just get a few maybe 6 scattered values.... 10Ohms, 47Ohms, 100Ohms 470Ohms 680Ohms for example.
    I wouldnt skimp on any of the values between 1K and 100k you will use lots of them you could just get a few selected values between 220k and 1 meg.

    Capacitors are a bit different, and unless you are doing specialist stuff common handy values would be ...

    0.01uF, 0.1uF, 0.47uF, in monolithic,
    1uF, 4u7, 10uF electro or tantalum rated ~ 25VDC
    22uF, 33uF, 47uF, 100uF, 1000uF, 2200uF and say 4700uF all electrolytic...
    maybe some at 25V and some at 50V
    you will find the 1000, 2200, 4700 values needed for power supply use

    none of those caps are overly expensive either and you could probably easily afford at least 10 of each

    cheers
    Dave
     
    Last edited: Apr 8, 2012
  3. KJ6EAD

    KJ6EAD

    1,114
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    Aug 13, 2011
    Last edited: Apr 8, 2012
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,295
    2,736
    Jan 21, 2010
    A lot depends on what you're going to be doing.

    If you were interested in digital electronics, I might recommend buying some 1k, 10k, 100k, and 1M resistors because when you use resistors their exact value is often not important.

    My suggestion is to check to see if they have packs of assorted resistors and similar for capacitors and buy them.

    I think I bought a pack of 500 assorted resistors about 20 years ago (it may have been 30 years ago) and they lasted me (for breadboarding) up until a couple of years ago when I bought another similar pack. When my eyes were better I could pick out the right resistor fairly easily, these days it's not quite so much fun...

    Capacitor packs tend to come in at least 2 types. One will include larger value electrolytics, the other smaller values. The packs I bought years ago still have remnants in my breadboarding "bin".

    The breadboarding bin gets refreshed from time to time as I have the odd component left over from something, and in it goes.

    If I were to be really organised, I'd probably split up the resistors by decade (1-0.0, 10-99, 100-999, 1000-9999...) just to make it easier to find values faster.

    Some people have suggested doing this split by E12 value, so you have in one bag 1, 10, 100, 1000, ..., and in another 1.2, 12, 120, 1200, ... and so on. The problem with this is that it's fine if you have E12 resistors (or only E12 values) and all you need to do is look for the correct colour multiplier, but t breaks down when you get E48 or E96 values which mean *way* more bags. The other problem is that when you go from 2 stripes plus multiplier to 3 stripes plus multiplier, the colour of the multiplier changes for the same value resistor (10k = 10 * 10^3 -- 3 bands, or 100 * 10^2 -- 4 bands).

    Jaycar have 4 packs of resistors. I would probably start with the 0.25W carbon film pack with 300 values for $6.95 (RR1680). I started off with something like their 1% metal film pack which is $14.95 for 300 resistors (RR0680). It's unlikely that you'll need the additional accuracy for breadboarding things, and if you need the additional power handling you can place a couple of resistors in series or parallel -- and that won't happen often. (The packs are on Page 73 of their catalog which costs $3.95 or you can get one with this month's Silicon Chip magazine.

    They also (Page 77) have 4 packs of capacitors. the electrolytic pack RE6250 ($11.95) contains 55 capacitors from 1 to 470uF (they will be various voltage ratings), and the greencap pack RG5199 (which are 100V and not many are green any more!) are $9.50 for 50 values between 0.001uF and 0.22uF.

    Somewhere in the past I also bought a pack of transistors. On Page 65 they have ZT-2170 $14.95 which has 100 common small signal transistors. For most uses you can split them into PNP and NPN and just pick one at random.

    Stuff for breadboarding is rarely critical (in fact very few components are critical in any design) so you can save some money by getting some of this stuff online. For low voltage use, buying resistors, capacitors, and transistors in packs like these from China is not likely to cause huge problems. Breadboards themselves can be very cheap to get from China, and although they're not the best quality, it can sometimes be useful to have a couple of them if you don't want to pull one circuit apart to make another.

    From ebay

    -- 1000 1/4W 1% resistors for $10 (search for "assorted resistors")
    -- 500 electrolytics for $16 (search for "assorted capactors")
    -- 100 transistors for $5.00 (search for "assorted transistors")
    -- Solderless breadboards 830 point for $6 (search for "solderless breadboard")
    -- Jumper wires 65 for $3.30 (from search above)

    The jumper wires are especially useful. They save you from having to scrounge up pieces of wire. If you want to scrounge them up, 1m of UTP cable (8 solid cores) will last you for ever. Just make sure you don't get the flexible UTP cable.

    edit: if you go the chinese ebay transistors, pick a selection of the 2Nxxxx transistors as I'm not sure exactly what the other ones are, and it's important to know what you've got and to be able to find specs on them.
     
  5. BobK

    BobK

    7,673
    1,684
    Jan 5, 2010
    You can get assortments really cheap on EBay

    Bob
     
  6. DGPILOT

    DGPILOT

    2
    0
    Apr 8, 2012
    Thanks

    thank you guys all soooo much, you have been very helpful, still wondering though, what does the % and the 1/4 W mean? is that really important, im mainly using arduino/microcontrollers, by the way im in year 9 so im not as genius, i only started with arduino 5 days ago, also ive seen there are carbon and metal film resistors, difference?
    thank you again, isnt it amazing how in just a day, you can get quality advice on the net :)
     
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,295
    2,736
    Jan 21, 2010
    Components are not perfect. When a 1000 ohm resistor is made, it won't be exactly 1000 ohms. It may be 995 ohms, or 999 ohms, or 1065 ohms.

    The tolerance (in percent) tells you how far they may differ from the marked value. A 5% resistor will be within +/- 2.5% of the marked value. Common tolerances are 1% and 5% these days, but in the past they were as great as 20%. It is also possible to get resistors with tolerances as fine as 0.1%, and specialised resistors with tolerances even finer.

    There are very few cases where 5% (or even 10%) will be a problem. Typically resistors are much closer than their tolerance would suggest.

    Power rating is more important. You calculate the power in terms of any two of voltage, current, and resistance. (V^2/R, I^2R, or VI). the result of this should be less than the power rating -- preferably significantly lower.

    So 9V across a 1k resistor will cause 9^2/1000 = 81/1000 = 0.081 or approx 1/10W dissipation which is lower than 1/4 watt, so you're fine.

    9V across 100 ohms results in 9^2/100 = 81/100 = 0.81 or almost 1W dissipation -- this is way over 1/4 watt at the resistor may start to smoke, or at least get very hot. It's value may be permanently altered by this.

    30V across a 3.9k resistor will cause 30^2/3900 = 900/3900 = 0.23W. This is very close to 1/4W and normally you'd use a 1/2W resistor for this to provide margin. On a breadboard with long leads to draw away the heat, and plenty of air around it, it may be OK (especially if it was only for a short period).

    capacitors also have tolerances which operate in the same way. Most important for capacitors is their voltage rating. Exceeding this may damage the capacitor. Some capacitors are polarised and connecting them backwards can destroy them.

    There are a wide range of specifications for components, but there are the big ones. Resistors also have voltage ratings, capacitors have current ratings and resistance ratings, and both have ratings for drift in value over temperature and time, but it is only very rarely that these things matter.
     
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