Newbie here. Trying to read the speed of a diesel. 003 does not seem to have pulse counter for my DO Hall effect module . How else can I read the speed of a motor? In what form does the signal need to be provided to the Imp 003? What type of pin do I need to use? My apologies for my ignorance. Thanks.
003 does have a pulse counter, on pinM - see https://developer.electricimp.com/hardware/imp/imp003pinmux/?q=hardware%2Fimp%2Fimp003pinmux%2F
You would need to ensure the signal transitioned between 0v and 3.3v (no lower than 0, no higher than 3.3) before feeding it to this pin. Generally powering the hall sensor from 3v3 achieves this.
A hall effect module is about the easiest way to read RPM 
Thank you for your very timely help. This worked right away. I love Imp.