This SmartElex RLS-08 Analog & Digital Line Sensor Array has 8 IR LED/phototransistor pairs, making it a great detector for a line-following robot. Each sensor has its own digital and analog output also a potentiometer to adjust the sensitivity of the individual sensors.
The TCRT5000 reflectance sensors array is intended as a line sensor, but it can be used as a general-purpose proximity or reflectance sensor. The module is a convenient carrier for eight IR emitter and receiver (photoresistor/photodiodes) pairs evenly spaced at intervals.
Each phototransistor equips a pull-up resistor to form a voltage divider that produces an analog voltage output between 0V and VIN (which is typically 5V) as a function of the reflected IR. The lower output voltage is an indication of greater reflection.
The outputs are all independent, but the LEDs are arranged in pairs to halve current consumption. The LEDs are controlled by a MOSFET with a gate normally pulled high, allowing the LEDs to be turned off by setting the MOSFET gate to a low voltage. Turning the LEDs off might be advantageous for limiting power consumption when the sensors are not in use or for varying the effective brightness of the LEDs through PWM control.
