Maker Factory ELECTRONICS EXPERIMENTS BOX Manual page 304

Circuit 150 to 152 An RC phase shifter chain (C1 to C3, R4 and R5) forms a time-delayed feedback from the
collector to the base. This produces undamped sine waves.
306
Fig. 3.149: Circuit 149 – Pin assignment of the
RS-232C interface
Fig. 3.150: Circuit
150: Simple 1kHz
tone generator
Fig. 3.151: Circuit 151:
Simple 100Hz tone
generator