PPR for rotary encoder

in my design, the motor is required to lift up/down a base with a constant speed within 5-8rpm, i m using incremental encoder as the speed sensor and PIC-16f877A to control the pwm, the motor is directly connected to the base as well as the encoder, can anyone guide me in determine the required ppr ? do i need any interface between the encoder and the PIC? thanks

Do we interpret you question as: "I wish to use a rotary encoder and need advice on its selection"?

If that's the case, look for spec's that indicate an output compatible with the PIC.

In general, the more pulses/revolution, the better the resolution.

Do you already have the encoder, how fast is normal speed or rpm. If you had a voltage porportional to rpm can your program then control speed? A relativley simple ckt can convert a pulse train to a voltage porp. to rpm.

http://www.ctiautomation.net/Accu-Coder-Encoders.htm

http://www.clrwtr.com/Kubler-Encoders.htm

Have you looked at Accu-Coder or Kubler encoders?

We should interprete your question as: "I wish to use a rotary encoder and need advice on its selection"? and i google your question, find a lots of similar problems. You could go to check them.