Resistors on schematics

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  • m3g4tr0n
    Senior Member
    • Aug 2011
    • 88

    #1

    Resistors on schematics

    what (tolerance / wattage) resistors should i use on schematics that list only the resistor value.
    -----------------
    eg.
    http://www.qsl.net/iz7ath/web/02_bre..._esr/index.htm

    R1=10K <--- do i use any tolerance and watts?
    R2=4K7
    .....
    R9,R11=1K 1%
    R10,R12=22 1%

    -----------------

    when checking eBay to buy resistors i see. 1w, 1/2w, 1/4w - 1%, 2%, 5%, 10%
  • PCBONEZ
    Grumpy Old Fart
    • Aug 2005
    • 10661
    • USA

    #2
    Re: Resistors on schematics

    Figure out how many volts are across it then use ohms law to find current and watts.
    Then use one rated higher.

    5% is the normal/common tolerance.
    If it's not marked you can assume it's 5%
    1% is usually found in things like test equipment.
    -
    5% are pretty cheap and common.
    Wouldn't buy 10% unless that's all I could find.
    .
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    - We should be more concerned about the Intellectual Climate.

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    Comment

    • romansroad
      Senior Member
      • Feb 2010
      • 123

      #3
      Re: Resistors on schematics

      Ohm's law is always best, but if you're working on a piece of gear and are replacing a resistor, you can estimate the wattage by comparing sizes on the board. If you're scratch building, then you're back with ohm's law.

      Comment

      • romansroad
        Senior Member
        • Feb 2010
        • 123

        #4
        Re: Resistors on schematics

        Originally posted by m3g4tr0n
        eg.
        http://www.qsl.net/iz7ath/web/02_bre..._esr/index.htm

        when checking eBay to buy resistors i see. 1w, 1/2w, 1/4w - 1%, 2%, 5%, 10%
        Now that I see the circuit you're building (sorry, missed the URL), 1/4 or 1/2 watts would be fine, and 5% tolerance would be fine as well. You probably already have a PCB with these parts on it, so you won't need to buy them. I mean, if you're building an ESR meter, I bet you have some old boards in your junk box....right?

        Comment

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