A RC filter and an NTC are connected to ADC2 and ADC5 respectively. These analog sensors are used as input to the ADC. But is is also possible to disconnected them by cutting the cut-straps on the top side of the board.
The RC filter (1. order low-pass) has an approximate 3dB cut-off frequency of 159 Hz. The input to the RC filter is one of the GPIO pins on the UC3 that can be configured to output a PWM signal to the RC filter. This can be used to generate a DC voltage on the output of the RC filter which can be measured on the ADC. As this is a 1.order filter, the ripple on the DC voltage is proportional to the input frequency. A higher input frequency will give lower ripple on the output.