Sun sensors are a commonly used instrument for attitude determination on spacecraft. These sensors come in multiple forms including ones with binary outputs for very simple systems. The two primary variations for satellites are coarse sun sensors (CSS) and fine sun sensors (FSS). Fine sun sensors are more accurate than coarse sensors but are also much harder to build and therefore more expensive. These sensors will output an analog signal corresponding to the level of sunlight they are receiving. The sunlight these sensors receive is proportional to the angle that the sensor is from the sun. Using multiple of these sun sensors you can determine the precise orientation of the satellite. How many sun sensors are required is determined by the accuracy of the sensors being used and the mission requirements of a given satellite.
For CSDC4 the SFUSAT ADCS team built the hardware for an attitude determination system using 16 coarse sun sensors. This system was actually beyond what was required for the payload of that satellite which had no ability to actively change its attitude. The data could, however, still be used to determine ideal transmission times and determine potential failures in orbit. The CSDC5 payload requires a high pointing accuracy which means a highly accurate ADCS system.
The CSDC-5 attitude determination system will adapt the sun sensor hardware previously developed and also add additional sensors. Although the other sensors are not yet finalized it will most likely use an IMU and horizon sensor(s).