Dawn Simulator

Or, the $600 light switch...

Ever notice how hard it can be to wake up when it's still dark outside? Between early worm hours in the winter, and Daylight Saving Time in the summer, it's been a real pain for us. My sister-in-law mentioned to us one could purchase products that would brighten a room gradually to help ease awakening. While products I found (most seemed to be alarm clocks connected to lights), I wanted a bit more sophisticated and controllable.

Since one of our computers runs 24 hours per day and is connected to the network in or home, the best solution seemed to be to create a networked dimmer and control it using software on a computer. I built such a system, which is comprised of the following components:

System Operation

The system is normally operated by the PC software. The only direct user action on the DawnSim hardware device itself is the "Cancel/Override" switch. When pressed while the PC software is controlling the device, the switch extiguishes the lamp. Otherwise, the switch toggles the lamp on and off (hence the "$600 light switch" subtitle above". Whenever the switch is pressed, it changes the system state to "cancel", and responds to all icommands received with "cancel" achknowledgements, until a "clear cancel" command is received, in order to signal the PC software to cancel the current dimming sequence. The LCD display continuously displays status and shows the current and previous commands receieved.


While the Dawn Simulator hardware and software may seem impressive, without the network and PC, the system isn't any better than a light switch. With the network and PC, it's a total system that provides a rather nice way to wake up in a steadily brightening room (like at dawn), even when it's dark outside (for workways, about half the year in our area). The scheduled PC software I wrote doesn't require any action from us, unless we want to change the schedule. While the end result was 2-3 times more expensive than commercial products I've seen, the end result is a totally hands-off system that requires almost no attention. It was also a lot of fun (and work) to design and build the system.

As hinted above, I spent about $600 building the system. Most of this was component parts (buying small quantities at retail is expensive), but some of it can be reused (such as the Basic ATOM Universal Development Board, for breadboarding the system, and parts leftover from the Bare Board Parts Kit, which contains parts for populating 2 boards). The enclosure itself was over $80. I could have cut corners, such as leaving out the LCD display and the DAC chip, but the overall reduction in expense would have been small (maybe $30). Besides, this was as much a learning experience as it was a task to build a usable product. For 2-3 times the price of a commercial product, I have a system with better capabilities and learned quite a bit in the process. As my spouse reminds me, there are worse ways to spend $600.

The only downside I've noticed is using the Velleman DC-controlled dimmer kit. My measurements show that I don't get more than about 40 light levels (which is probably enough) and the output doesn't increase linearly with increasing input voltage. I used an oscilloscope to verify that each dimming level from my hardware provides a 150mV increase to the dimmer and checked/rechecked the wiring ad nauseum; therefore, either I have a lemon or Velleman has a design problem. The dimmer also requires the lamp to be connected and turned on at power-up; otherwise, the dimmer doesn't detect the presence of the light bulb and won't operate. While these problems are a drag, using the kit was still better than trying to build the dimmer myself and the price was very reasonable ($35).

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Copyright 2001-2009, Tim Sharpe. You are free to use this information for personal, non-commerical use without restriction. All rights reserved for commerical, organizational, or government use. Questions or comments to tim@beaststwo.org. Flames to /dev/nul.

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