Check out this schematic. What's with the resistor values? They're probably nearly impossible to find, no?

http://circuitzoo.com/wp-content/up...-Generator-Circuit-Design-using-555-Timer.png

 

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...

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

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

 

what makes this one better?

 

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.

 

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?

 

Hello,

I think he is pointing at the 2.4 K and 6.2 K at the left 555.
Those are standard E24 values, take a look at this table:
http://www.educypedia.be/electronics/resistancevalues.htm

The table comes from the EDUCYPEDIA page on component codes:
http://www.educypedia.be/electronics/datacomponent.htm

Bertus

 

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...

 

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?

 

Hello,

The lamp in the schematic is there for stabilization:

A led in that place will not work.

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

Bertus

 

FWIW, there's a *very* useful odd resistance finder chart at...

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.

 

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.

 

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)

 

Are you referring to the triangle? It is an alternate symbol to ground.

 

No. It's a circle with a + - in it. It looks sorta like a motor?

 

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.

 

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.

 

Hello,

The part you mean is a voltage reference.
Here is a page from the referencebook of the AAC:
http://www.allaboutcircuits.com/vol_5/chpt_9/2.html

Bertus

 

merci beaucoup!