IR proximity sensor for automatic spraying
Depending on what type of human proximity you are trying to detect, here are a couple of options that might work well:

Method 1: If you are trying to detect motion, the cheapest way is to use a photodiode or CDS cell connected with a pulldown resistor and read by one of your PIC's ADC pins. You will need to write an algorithm that senses rapidly changing values on the ADC pin, which will indicate some sort of motion. If you want a narrow detection area, you can use a tube over the photodiode as a blinder. 

Method 2: If you are trying yo detect proximity by using an IR source and measuring its reflection from an object within proximity, you already have the correct setup. However, you will need to check the datasheet of your IR receiver module for its carrier frequency. I think 30Khz to 40Khz is the most common. You can use the hardware PWM pin on your PIC to constantly produce this carrier frequency on one of the IR LED pins. Connect the other pin of the IR LED to an IO pin on your PIC. Now you can send pulses or even serial data to that pin and it will automatically have the carrier frequency on it. With IR proximity, however, you will always run into the trouble of not being able to detect non-reflective dark objects. In which case, see method 3.

Method 3: Use an ultrasonic transducer for proximity detection. Typically two are used. Use one for pinging a pulse (at the resonant frequency) and use the other for detection. You will most likely need an op-amp or comparator circuit to amplify the output of the receiving transducer for greater ranges. The benefit of this method is being able to calculate exact distance to your object based on the flight time of the "ping" and its return. Flight time will be approximately 1/2 the speed of sound since the "ping" has to travel to the source (1) and back (2).