I'd scrap the speed calculation, put an "analogWrite" into "setup" on a spare PWM pin set to a 50% duty cycle, and see if you can measure the PWM frequency of around 490Hz by connecting the PWM pin to your input pin..
I'd scrap the speed calculation, put an "analogWrite" into "setup" on a spare PWM pin set to a 50% duty cycle, and see if you can measure the PWM frequency of around 490Hz by connecting the PWM pin to your input pin..