Hi everyone,
i built a 555 timer RC circuit and connected it to an oscilloscope in order to test the frequency. Why are my practical values slightly more or less that calculated theoretical values? My two resistors and one capacitor each has a tolerance of 10%. Is there another reason (other than tolerance) for the variation between results?
Alex

 

It's all the tolerances, including the R and C.
The 555 timer itself has tolerance variations as to where exactly it switches on the RC timing waveform.

 

Use CMOS 555(e.g. 7555) for more accuracy.

 

Use CMOS 555(e.g. 7555) for more accuracy.

Why would that help the accuracy?

 

CMOS 555 is different in max Freq , min supply voltage , noise characteristic , temperature stability and of course output power.
In addition usually cmos versions have better production quality.

 

In addition usually cmos versions have better production quality.

What does "better production quality" mean compared to the bipolar process?
What's the basis for that statement?

 

I said usually. Maybe you did not understand my statement,Or It is my fault.
I said better production quality deferential , Does not relate to the method of production.The matter is producer.
Probably my statement is not apply to your area.
In meddle east Electronic components usually are Chinese fake and low quality products specially in Iran thanks to west sanctions!
I think You understand what I mean.Don't you?

 

I said usually. Maybe you did not understand my statement,Or It is my fault.
I said better production quality deferential , Does not relate to the method of production.The matter is producer.
Probably my statement is not apply to your area.
In meddle east Electronic components usually are Chinese fake and low quality products specially in Iran thanks to west sanctions!
I think You understand what I mean.Don't you?

Basically.
But I don't see that fake Chinese CMOS parts would be any better than fake Chinese bipolar parts.
Since the sanctions have apparently been relaxed (although not without a great deal of controversy here) hopefully you'll now have a wider choice of suppliers.

 

The process of growing matched resistors on an IC substrate is not significantly different for bipolar and CMOS fab lines. Therefore, both types of 555 should contribute approximately the same range of errors, usually around 1-2%.

You don't say what the actual error is between your calculated and demonstrated frequencies, but with 10% components it is entirely possible for the error to be over 20%.

ak

 

Don't use the 555 for precision timing. If ± 20% isn't close enough for you, then you need a better timing circuit.

 

Basically.
But I don't see that fake Chinese CMOS parts would be any better than fake Chinese bipolar parts.
Since the sanctions have apparently been relaxed (although not without a great deal of controversy here) hopefully you'll now have a wider choice of suppliers.

Coooomeeeee Onnnnnnnnn,You did not understand what I mean finaly likely,You are very familiar with bipolar components and love their suppliers
Forget it,SLK001 is right,555 is not applicable for precision timing(at least bipolar 555 ) ,Use IC using crystal oscillator such as 4060
or Interface a DS1307 with a cheap Attiny13 ,So have a lot of option too.