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need some advice about the lm555

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A stable capacitor: Silver mica, mylar, polystyrene, etc
 
does anyone know whats the best capacitor to use with the lm55 in creating the oscillator?

You didn't specify exactly how accurate the frequency needs to be.
A ceramic cap with X5R or X7R dielectric type is very good for stability and initial tolerance and is way cheaper (and smaller physical size).
 
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haha no im not trying to scare off animal, im trying to build a walking stick for the blind that has a sensor on it, so when the stick approaches an object thats close it will generate a sound through an amplifier. i am aware that the guide dog might be annoyed with it and go insane.

sorry for not specificing the stability of the frequency. the the frequency range is -+5% of the 40khz, so thats 38KHZ< X < 40KHZ. i have thought of using electrolytic, but i was told by someone that it would not do the job at all

i have another question though, would this oscillator drift? as in its not very stable with the 555?
 
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Using good metal film resistors, and a good capacitor, it will be stable enough, especially if the 555 runs on a regulated supply.
 
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