Bike light statefulness resumed
Jan. 15th, 2013 12:42 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
jackI tried popping the battery a dozen times. Each time the light was on beforehand, it was on when the battery went back in. Each time it was off beforehand, it was off when the battery went back in, but came on when I pressed the button.
I tried leaving the batteries out for half an hour once in each state and it still resumed "on" or "off" as appropriate.
Now, that was very informal, so it's quite likely that I biased the test by seeing what I expected to see at some point. But it seems that it's deliberate, not (a) it defaults to always-on if the connection is interrupted (b) there's a residual signal without being deliberately designed that way (c) it's random, etc.
I agree that it makes sense that it's designed that a brief interruption in power doesn't turn the light off (or on) so if it's jolted you're not cycling in the dark. But I'm surprised that it can remember.
What's most likely? Is it plausible there's a capacitor acting as a single bit of persistent memory? Or powering a flip-flop (for 8 hours?). Or is something else a simpler implementation of one bit of non-volatile memory?
I tried leaving the batteries out for half an hour once in each state and it still resumed "on" or "off" as appropriate.
Now, that was very informal, so it's quite likely that I biased the test by seeing what I expected to see at some point. But it seems that it's deliberate, not (a) it defaults to always-on if the connection is interrupted (b) there's a residual signal without being deliberately designed that way (c) it's random, etc.
I agree that it makes sense that it's designed that a brief interruption in power doesn't turn the light off (or on) so if it's jolted you're not cycling in the dark. But I'm surprised that it can remember.
What's most likely? Is it plausible there's a capacitor acting as a single bit of persistent memory? Or powering a flip-flop (for 8 hours?). Or is something else a simpler implementation of one bit of non-volatile memory?