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NJM567 V LM567 - Tone Decoder Formula Help

Discussion in 'General Electronics Discussion' started by stuart sutherland, Aug 8, 2019.

  1. stuart sutherland

    stuart sutherland

    11
    0
    Jul 6, 2015
    All,

    I am looking at two devices:

    1. NJM567 (Made by JRC then Phillips)
    2. LM567 (Made by TI)

    These look fundamentally the same. The data sheet for each looks identical (same equivalent schematic). However, the formula quoted for calculating the central tone frequency differs in both data sheets (I have attached both).

    1. Fo = 1 / (1.07 x R x C)
    2. Fo = 1.1 / (R x C)

    Before I start designing I want to understand why these are different?
    I cant understand why they would be from the data sheets.

    Does anyone have any experience in using either device and can fill in the blanks?
    I thought equation 2 would be one I used, however I got confused when I seen the formula in data sheet 1.

    Many thanks,
    Stuart
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    9,137
    1,846
    Nov 17, 2011
    No experience with these chips, but: Look-alike components do not necessarily have to be identical. Small variations in parameters may lead to small differences in behaviour. Not uncommon. Use the formula that matches the specific chip you are using.
    Then again: The equations differ by ~17 %. If you use standard capacitors (20 %) and resistors (10 %) the change in center frequency implied by component tolerances is higher than that. As a one-size-fits all solution you could just as well use f0 = 1/(R*C) for designing the circuit.
     
    (*steve*) likes this.
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