I spent this morning working on the SmartClock; however as it turns out there might be more to it than I originally thought. In case you've just tuned in, the idea was to outfit a standard clock radio with a miniature motion sensor (specifically a Panasonic NaPiOn sensor) and a PIC microcontroller to shut off the LED display whenever the room the clock was in was empty.
Figure 1: Prototype controller (center), Panasonic NaPiOn motion sensor (top left)
The four-pin connector is for the anodes of the LED display, the three-pin connector in the middle goes to the motion sensor, and the six-pin connector on the left side of the board is dual-purpose: when the board is in the radio it acts as a power supply input, and when it's on the bench it acts as a ICSP port for the PIC programmer. As I was wiring this up I was thinking to myself "There's no way in hell I can ever let anyone see this", but here it is - the worst rat's nest of wire wrap I've ever seen:
Figure 2: Ahhhh!!! (well, I guess it is October - It's a Halloween project)
The Rats' Nest
First off: Don't ever wire anything like. Ever. In the top left we have two ST Microelectronic D10F10 N-Channel MOSFETS that control the anodes of the clocks' LED display. They are driven by the Toshiba TLP191B photocoupler (beige) in the bottom-center. The PIC12F629 is on the left side of the board (on the top side), and in the top-right we have the LM1086-3.3 LDO regulator.
The idea was that by switching off the LED display when the room was vacant it would be possible to save a considerable amount of power over the clocks' lifetime (ballpark figures are found in the original post). After wiring this thing up and plugging in the radio I was disappointed to find out that the radio's current draw actually increases by about 1mA when the display shuts off. As this defies logic I will have to look into this some more, however it is obvious that in it's current state we aren't achieving the goal of power savings.
Room for Improvement
- Better firmware (slower clock speed, sleep timers, etc)
- Better hardware (more efficient power regulator, lower power PIC)
- Less wire wrap
Though the idea of starting with a working clock radio seemed like a good idea at the time; in retrospect it would have probably been a better idea to start from scratch and build an entire clock from the ground up with power conservation in mind. Since the clock I'm using probably wasn't designed to be overly power conservative there are likely unnecessary losses in the power supply and the rest of the circuity already present in the clock.