strange resistor values

Discussion in 'General Electronics Chat' started by ale2121, Sep 10, 2010.

  1. ale2121

    Thread Starter Active Member

    Mar 20, 2009
    71
    0
  2. Wendy

    Moderator

    Mar 24, 2008
    20,764
    2,534
    No. I have all of them in my personal resistor stock. Which ones are you having trouble with?

    BTW, if you want a better PWM circuit...

    [​IMG]

    LEDs, 555s, Flashers, and Light Chasers
    Chapter 5

    It does 0% to 100% while maintaining a stable frequency.
     
  3. ale2121

    Thread Starter Active Member

    Mar 20, 2009
    71
    0
    what makes this one better?
     
  4. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
    312
    11 components instead of 14 is one thing that is better.

    What are you trying to do? There may be a much better circuits for you.
     
    ale2121 likes this.
  5. Wendy

    Moderator

    Mar 24, 2008
    20,764
    2,534
    Not much, except it is much more straight forward. You exceed 100% with the design you show and you will get some very anomalous results, it will start missing. You can reduce the parts count even more with what I showed.

    Again, what resistors are you having trouble with?
     
    ale2121 likes this.
  6. bertus

    Administrator

    Apr 5, 2008
    15,638
    2,343
    ale2121 likes this.
  7. Nik

    Well-Known Member

    May 20, 2006
    55
    3
    I ran into similar issues biasing an LM334 (*) current source because my high-street supplier only stocked sub-10R values of E24 series in E12. Okay, they were all 1%, so I could series/parallel to get what I wanted...

    (*) i = 67.7/R mA (at 20~~25'C), but specification allows +/- 3% so measure current delivered. It will probably be within ~1.5%, but check anyway. And you did read those teeny colour bands right ??

    FWIW, there's a *very* useful odd resistance finder chart at...
    http://skywaves.demon.co.uk/technical/Teaching/Odd_Resistance_Finder.pdf

    Just remember to respect components' 1%, 5% or 10% value...
     
    ale2121 likes this.
  8. ale2121

    Thread Starter Active Member

    Mar 20, 2009
    71
    0
    Thanks all!
    I'm just trying to build a simple audible sine wave oscillator. I was looking around at various schematics, and came across this one, and the values struck me funny, so I thought I'd ask. I found a schematic in a book that uses a TL081 op amp, which I'd prefer to use since the 555 can't put out a sine wave, and it just so happens I have some TL081s laying around. I found this schematic: http://www.electro-tech-online.com/...743320-sinewave-oscillator-oscillator_700.jpg

    I can't seem to get it working, though I only stuck an LED in there, instead of the 12v lamp it's asking for. If I were to stick the speaker on pin 6, that should put out something, correct?
     
  9. bertus

    Administrator

    Apr 5, 2008
    15,638
    2,343
    Hello,

    The lamp in the schematic is there for stabilization:

    [​IMG]

    A led in that place will not work.

    Take a look at figure 15-10 of the attached PDF.

    Bertus
     
    Last edited: Sep 12, 2010
  10. someonesdad

    Senior Member

    Jul 7, 2009
    1,585
    141
    Here's a program that yields something similar; it can be used with the resistor values you have on hand. Read the PDF files to see what the tools do.
     
  11. Wendy

    Moderator

    Mar 24, 2008
    20,764
    2,534
    To expand on what Bertus said, the lamp is a negative resistance. It is use as part of an automatic gain control to make the sine wave a pure signal.
     
  12. ale2121

    Thread Starter Active Member

    Mar 20, 2009
    71
    0
    Hey Bertus,
    Thank you. I saw that pdf. Anyone know where I can find that lamp? TI-327? I also have no idea what that symbol at the bottom of that schematic is (Vref .833 v)
     
  13. Wendy

    Moderator

    Mar 24, 2008
    20,764
    2,534
    Are you referring to the triangle? It is an alternate symbol to ground.
     
  14. ale2121

    Thread Starter Active Member

    Mar 20, 2009
    71
    0
    No. It's a circle with a + - in it. It looks sorta like a motor?
     
  15. Wendy

    Moderator

    Mar 24, 2008
    20,764
    2,534
    I think you're going to have to define which schematic you're talking about. The only one I could find that comes close is in post #9.
     
  16. ale2121

    Thread Starter Active Member

    Mar 20, 2009
    71
    0
    Oh. In that same post, Bertus attached a pdf, and he was addressing figure 15-10 in that post. There's a symbol at the bottom of that figure, and I don't know what it is.
     
  17. bertus

    Administrator

    Apr 5, 2008
    15,638
    2,343
  18. ale2121

    Thread Starter Active Member

    Mar 20, 2009
    71
    0
    merci beaucoup!
     
Loading...