• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

HElp me plz

Not open for further replies.


New Member
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...

Waiting 4 ur reply......



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.


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
Not open for further replies.

Latest threads

EE World Online Articles