Serial bi-directional (one-wire half-duplex) digispark device works however answers itselfs
Based on that schematic, that's exactly how it will react on your pc console program with or without something attached at the other end. You tied the tx to the rx, essentially a loop back device. Ignore the "echo".

As for your digispark not responding, have you set your console at the right speed and parity and stop settings?