Now for the fun part. This alarm clock is based on a single integrated circuit that contains all the basic functionality of an alarm clock, the LM8560. It really is an alarm clock on a chip, including drivers for 7 segment LEDs. Basically, you hook up power, switches, and a display, and it does the rest. However. For an alarm tone, it produces "900Hz 2Hz intermittent (50% duty) modulation signals". Basically, that annoying "Beep beep beep" cheap alarm clocks produce. And that's straight out of the chip. There's no "alarm on" or "alarm off" out of the chip, just the intermittent. That's absolutely no good to me. I need to run a motor and LED, both of which require constant DC current. So there are 2 ways to go. Either set up a funky system for detecting the intermittent, switching on a relay when it starts, and switching the relay off when it's stopped for more than a second. Or ... "When the need arises, a filter can be applied to alter the alarm signal to a DC signal". So today we learn about low pass filters! The thing to note here is that the annoying beep is only an annoying beep because it's hooked up to a speaker. Speakers are, of course, activated by current, which means what you actually have here is usable current that's being switched on and off twice a second (2 Hz). What a low pass filter (or really, what an "RC Circuit" (Resistor-Capacitor) does, because that's what I'm using, which happens to also be a low pass filter) does, in effect, is store some of that current while it's on, and then release it while it's off. The standard capacitor analogy is a good one here - it's a rain water tank.

That's my understanding, anyway :) Of course, I haven't built it yet. There will be pics when I have.