# HElp me plz

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#### mohdfasieh

##### New Member
Hello
I am new bie in the field of Electronic Engineering. I want to generate a frequency 38KHZ using 555 timer in Astable mode.
i have used the formula F=1/(.693*C*[R1+2R2] )
So i have done Reverse engineering and put 38Khz in formula and Capacitor value of 1 MICROFARAD and i get the relationship that R1+2R2=37.9
So i have used R1=27.2 ohm and R2=5 ohm in my circuit .

Bus problem is that when i build the circuit i don't get desired output of 38Khz from PIn 3 of 555.

So an body help me in selecting proper practical values of R1 ,R2 and C.
Bcoz when i put my multimeter on Continuity and place it across 5 ohms it starts beeping .So
Does it mean that when i use this 5 ohm resistor in b/w 6 & 7 pin of 555 will it be short ckted. Bcoz multimeter is continously beeping when i put my probes on 6 and 7 pin of 555.....

In short plz tell me appropriate practical values of R1 R2 & C...

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#### Hayato

##### Member
When you create a new thread don't do that!

Use higher values resistances. Higher than 1k, for that, lower your capacitor value. Use a 2.2nF ~ 1.0nF and redo your math.

#### SPDCHK

##### Member
If you are looking for an accurate 38kHz, forget using the 555. Temperature change will change the frequency.

You need to use a crystal oscillator. Something like this. Substitute the crystal with the desired frequency crystal

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