Is there an automatic timer to record how long I've been playing a digital piano?

Question

I'm looking for a timer, an "hour meter" if you will, that will automatically time my playing of a digital piano. It could work on the headphone output, so that when it detects audio it starts counting, and after the audio stops it stops after a small delay. It would need to be completely automatic - no "push start" or "push stop" (I could use a plain stopwatch for that). This way I could know exactly how long I've been practicing/playing.

Something equivalent to this, only triggered by audio: http://pitposse.com/hourmeter.html?OVRAW=hour%20meter&OVKEY=hour%20meter&OVMTC=standard

I've tried searches for "audio timers", "appliance hour meters", etc. and so far no luck.

If you're electronically inclinded, seems like a 555 timer attached to a counter/display thing would work. I considered making a 555 one-shot and have the output drive a relay that was wired into a standard cheap stopwatch... hmmm.

Help?

Answer 1

It may be easier to get a "power meter" that measures how much power your digital piano consumes.

The device below also keeps track of time.

http://store.altenergystore.com/Meters-Communications/Meters-Battery-Monitors/Power-Meters/4-1850-15A-120VAC-1850W-POWER-METER/p284/