Hey there, thanks for the post! Glad you like the Metronome project, and I have some good news for you. The second version of the Tactile Metronome (TM2) has a simple line-out capability, where it generates a pulse on one of the pins every time it beeps! On the TM2 there's an "expansion header" on the bottom of the PCB, with labels G V B X S P, which stand for ground, Vcc, Beep, eXpansion, sync, and PWM. The expansion and sync pins don't do anything yet, and the PWM is just the pulse-width-modulation output that drives the beeps of the piezo element. Ground and Vcc are straightforward.
The Beep pin outputs an active-low pulse that is normally high, but goes low during each beep. You could use this to drive something external such as lights, motors, external sequencers or synthesizers, etc. Below is a photo of a waveform I just captured of this output.Every-beep output pin on Tactile Metronome
, on Flickr
Hope this helps! Let me know if you have any other questions.