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Increase Accuracy

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Powzoom

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Is it possible to increase the accuracy of a 555, or any square wave, by running it at 10X the desired frequency and then dividing it by 10? Would this make it more precise?
 
I need a circuit that varies 10:1 in frequency and stays frequency stable, less than 1%, and the duty cycle needs to be 50.0%. I know the diode modification to the 555 for 50% DC but would it be an accurate 50%. Less than 1% is what I'm going for. I know about crystals but I don't have one on hand right now.
 
I need a circuit that varies 10:1 in frequency and stays frequency stable, less than 1%, and the duty cycle needs to be 50.0%. I know the diode modification to the 555 for 50% DC but would it be an accurate 50%. Less than 1% is what I'm going for. I know about crystals but I don't have one on hand right now.
Stable as a function of what: Temperature? Supply voltage? Component aging?
The duty cycle you can do with a D or JK flipflop, configured as divide-by-2. It will be stable, unless your frequency is high relative to FF propagation delays and their variations.
 
Does it need to be continuously adjustable between 1 and 10, or do you just need 1x and 10x, or do you need 1x, 10x, and a couple of stops in between? If you could say the exact frequency or frequencies you need it would help.

For example if the frequency is very low you might have to use an electrolytic cap with the 555, and that would never give 1% accuracy. But if it was a high frequency you could use a 1% polypropylene capacitor and a 1% or tighter resistor and you could get more accurate and stable than you ever would with an electrolytic.
 
555s, RC and LC generator/oscillator circuits are not designed for good accuracy or precision. The best you're going to be able to do is use a checked Mylar cap against a metal film resistor, and even then, for 1% accuracy, you're going to have to use components with an accuracy of 0.75% or better or at least checked to 0.75%, including the tempco. If you need more accuracy, use a crystal oscillator at a mininum (it's more than good enough for 1%, typically good for 0.01% to 0.001%) and divide it down. What you won't get with an XO is variable frequency.

Dean
 
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