Karen's Learning Circuit Presentation:


The Learning Circuit 39: Inductor Project: Battery Juicer


got me to playing around with the Battery Juicer Circuit also called the "Joule Thief". You can check out her blog for a schematic and some suggestions. For her build she made a flashlight but I had other ideas for a good use.


When I finally crash at night I put my watch next to the bed. Unfortunately it is quite dark in the room so if I wake up and want to know what time it is I have to turn on the light on the table next to the bed. This usually wakes me up more than I want to and it also disturbs the boss. When I saw the nice low level light produced by the LED in Karen's experiment it dawned on me that this would be a perfect night light and watch reading light for the bedroom.


A couple hours and about 3 feet of 12 gauge copper wire later I had "The Watch Stand"



The watch stand runs on dead AA batteries that won't even power a wall clock. The circuit is the same simple circuit demonstrated in the Learning Circuit. I used a common mode inductor from a switching power supply, a salvaged NPN transistor from an old CFL light bulb circuit, a single AA holder, and the other electronic components needed to complete the build. A small push latch switch was also installed so the unit could be turned off when not in use. No sense wasting those stolen joules. It looks a bit strange, perhaps a bit like the Lunar lander, but it fits well with my sense of the aesthetic.


Here are a few more pictures so you can see it from a few different angles:




The yellow light diffuser that I have placed over the LED so that I do not get a sharp reflection off the watch crystal is something that was acquired over 50 years ago and has been patiently waiting in my Bulb Sockets box for a practical use.


Electronics is fun and inspirations are to be found everywhere we look. Thank you to Karen and the element14 Learning Circuit for a fun project.