Is the internal clock not good enough???

i having problem new project made , i'm not 100% sure cause is, 1 mhz internal clock not enough??

i have made navigation light controller model airplane reads pwm , changes modes accordingly. worked perfect when had project on uno moved on attiny84 , getting random episodes of lights blinking/skipping beats when not supposed to. happen 3-10 times minute , wont 2-3 minutes.

i checked output voltage on airplane , stable fluctuates max of 0.02v once in while.

i checked pwm airplane (used uno) , pwm varies +/- 4usec (hysteresis in code allows +/- 100usec variation)

what think problem is, internal clock skipping beats/jittering causing pwm read inaccurately (either high >2500usec or low <500usec) making lights default off mode


would running @ higher 8mhz internal better or
will better idea use external 1 mhz crystal, or there else should looking into???

have tried @ 8mhz internal? it's easy change if not work.

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