QTR-3RC Reflectance Sensor Array The QTR-3RC reflectance sensor array requires digital I/O lines to take readings. The similar QTR-3A reflectance sensor array is available with analog outputs. Functional Description The QTR-3RC reflectance sensor 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 three IR emitter and receiver (phototransistor) pairs. With sensors spaced at intervals of 0.375 (9.525 mm) along of the boards longer axis, this array works well as a minimal detector for line-following robots, as line-following courses are commonly made using 3/4 (19 mm) black electrical tape. The middle sensor is slightly offset along the short axis of the board. To use a sensor, you must first charge the output node by applying a voltage to its OUT pin. You can then read the reflectance by withdrawing the externally supplied voltage and timing how long it takes the output voltage to decay due to the integrated phototransistor. Shorter decay time is an indication of greater reflection. This measurement approach has several advantages, especially when multiple units are used: No analog-to-digital converter (ADC) is required Improved sensitivity over voltage-divider analog output Parallel reading of multiple sensors is possible with most microcontrollers The LED current-limiting resistors are set to deliver approximately 17 mA to the LEDs when VCC is 5 V, making the total board consumption just over 50 mA. The schematic diagram of the module is shown below:This schematic is also available as a downloadable pdf (117k pdf). For an alternative array with eight sensors and the ability to turn off the IR LEDs to limit power consumption, consider our QTR-8RC reflectance sensor array. For individual reflectance sensors, consider our QTR-1RC and QTR-L-1RC. QTR sensor size comparison. Clockwise from top left: QTR-3RC, QTR-1RC, QTR-L-1RC, QTR-8RC. Specifications