LightBot is a simple robot. He stands still and tries to look real cute in a robot sort of way. And as it gets dark, he lights up his glowing red eyes. If you are looking for such a companion for your desk or shelf or a kids room, LightBot might be just the right character for you !
Step 1: The Character
LightBot is a nice and easy project. You can print out his pattern from the accompanying pdf file, glue it to a piece of thin wood of your choice, give it a coat of clear lacquer or equivalent for durability, and when dry, carefully cut it out with a scroll or coping saw. I made two LightBots this way with a 1/8" thick wood back, and two on 1/4" thick wood. If that is all the robot cuteness you need, glue a small block on the bottom of the backside so he will stand up all by himself, or glue on a magnet so he can stick to a refrigerator. If you want him to glow red eyes in the dark, drill two holes for LEDs and two tiny holes for the Photoresistor, and read on.
Step 2: The Electronics
This dark detecting circuit shown here uses very little power - averaging roughly 1mW over the working life of the batteries. The chart shows the measured current draw versus battery voltage. So two AA batteries will power it for a long long time.
You will want to use high brightness red LEDs so that LightBot will still shine well as his batteries slowly drop in voltage over the months. You'll need an LDR (light dependent resistor), a general purpose NPN transistor like a 2N3904, and two resistors, 470K and 2.2K ohms. Also a AA battery holder for two cells. Breadboard the circuit and try it out for a few days and nights before soldering the components together.
Step 3: Making the Circuit
The photographs show the circuit soldered together in the back of LightBot's head. If you used the same components as on your test breadboard, and hook up correctly, it will work first time. The battery holder is attached with double sided foam tape. Note the narrow wood border frame glued in place around the back of the head. This allows fitting a plain back cover to hide the electronics as can be seen in a later photograph.
Step 4: Moveable Arms
Giving LightBot positionable arms greatly increases his robot cuteness! It requires the thicker wooden backing; I used 1/4" thick cedar. After cutting his complete form out, drill into each shoulder for a pivot pin; 1/8" diameter is perfect. Then cut his arms off along the body. Drilling before cutting ensures perfect alignment of the arms with the body. Then cut some short lengths of 1/8" dia. rod for pivots; I used brazing rod. I find that drilling into wood with an ordinary twist drill invariably leaves a hole that quite snugly accepts a metal rod of the same nominal diameter. The arms will be moveable but will stay where you put them.
Step 5: Magnetic Hands
I fitted a tiny magnet in each arm so LightBot could 'hold' things, like paper clips or even electronic parts. He looks even cuter holding stuff ! Of course with magnets as 'grippers', he only hangs onto things that have some iron in them somewhere. In the second picture he has 'grabbed' onto a screw in one hand and a junky bottle cap in the other. The magnets can be clearly seen in the third photo here. The magnets I used are 1/8" dia. by 1/8" long, but longer and slightly larger in diameter ones could be fitted for a stronger grip. They were pressed into 1/8" dia. holes with a little bit of super glue for security.
Step 6: Make More Than One !
LightBots make good gifts for kids - or even for certain 'grownups'. So while you are at it, you could make a family of them. A child or grandchild can even help - with gluing the pattern, maybe with cutting out, but especially with the soldering after everything else is ready. I cut out four LightBots and intended to keep a couple for visiting kids to solder up, but must have gotten got carried away when soldering the first one - and ended up finishing all of them before realizing I should have stopped after that first one ! Guess I'll have to make some more now.