I'm using some infrared sensors that use a LED and phototransistor, which both require a voltage to operate. I also have a 12v clip that is powering some motors through a driver chip. Is it safe to power these sensors (with the appropriate additional series resistance) from the motor supply? Will motor operation affect the sensors if the supply is used this way?
Is it safe to power these sensors (with the appropriate additional series resistance) from the motor supply?
Yes but make sure the signal going into your arduino is no greater than 5V.
Will motor operation affect the sensors if the supply is used this way?
There is always that possibility because motors generate interference. Good supply decoupling is often very important.
http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html