Solar powered robot ornament wishes you holiday greetings during the day but when the lights go out radios home for reinforcement.

Step 1: Parts:

Electronics:

2N3904 Transistor
Rectifier Diode
1M resistor
Blinking LED
2 Rechargeable 1.5v batteries
Solar panel

Misc. Parts:

Copper plumbing parts
Grommets
Rivets
Brass & copper wire
LED holder
Copper mesh or beer can
Spring
Epoxy
Hot Glue

Step 2: Battery:

For some of these I used 2 cells from a rechargeable 9v. Others I used rechargeable button cells. Be careful soldering to batteries.

Step 3: Circuit:

I found the circuit I used here: http://grant.solarbotics.net/images/Circuits/LO_DarkON.gif

I really like the simplicity of this circuit and wish I had done a better job showing it off.

Step 4: Robot Shell:

I decided to use copper plumbing parts because I had them on hand but this part could really be anything that has enough room to put the electronics in or on.

Drill holes in the end cap for the eyes and in the body for arms, belly button, satellite pole and wires. I use a hand drill and go slow, starting with a small bit and stepping up bit size incrementally.

I made the mouth with a Dremel and a cutoff wheel, but a hacksaw would work fine.

If you're feeling fancy and/or have them on hand finish the holes with aluminum grommets. On some I just used rivets for eyes on others it's a grommet + rivet mix.

Step 5: Soldering Arms:

I used a small hobby torch to solder the wire arms onto the body. Spending some time fitting the wire so it makes good contact with the inside of the body will make for a much stronger joint. I also sand both pieces I'm soldering right before.

I went with a four finger hand approach because it was easier to use small V's of wire.

I like to pretty much get the arms and fingers into position at this point because If you didn't do a very good job soldering they will break off. It's easier to fix now without the electronics inside.

Step 6: Satellite:

This could also be anything that kind of resembles a dish. I happened to have some fancy copper mesh/fabric, so I went with that. If this part seems like a pain, you can cut out the bottom of a beer can and use it as is.

If you have the fancy copper you still need a beer can. Turn the can over and gently work the copper mesh into the bottom, I used the handle end of a screwdriver. Once you have the shape cut the excess off with scissors.

Punch the hole in the center after you form the dish, if you do it before the hole will warp and spread.

I also solder some wires onto the led at this point. The led holders I used have a rubber cork that has to be on the led before soldering.

Step 7: Get Ready:

Turn the body over and put a piece of tape at the bottom of the neck, this is important because at the end we will be pouring epoxy into the neck.

When I used the 9v cells I kept the batteries on the outside like a backpack, with the button cells I just stuffed them inside. Either way we need to get those leads ready, either though a hole in the neck if they will be on the outside, or out on the desk if they will be inside.

The LED wires need to be strung through into the interior.

The leads for the solar cell need to be put through the belly button, better too long than too short.

Step 8: Solder the Circuit:

NOTE: Diode terminology is confusing, I'm going to call the end of the diode with the white stripe the negative (-) terminal.

Solder the components together.

STEP 1:
+ Solar
+ Battery
Resistor
+ LED

STEP 2:
PIN 1
- Battery
+ Diode

STEP 3:
PIN 2
- Solar
- Diode
Resistor

STEP 4:
PIN 3
- LED

After you have it soldered together cover the solar panel and make sure the led starts to blink. Tape everything up so the leads don't touch and fold it into a shape that is going to fit inside.

Step 9: Attach Solar:

Solder the solar panel to the leads. Carefully position the panel into the hands. Flip over and hot glue panel in place. I also use hot glue to hold the electronics inside.

Attach satellite dish to pole and position at a rakish angle.

Step 10: Put Your Head On:

Use epoxy to glue spring inside the head. After it cures mix another batch of epoxy and pour into the neck, hold head in place until epoxy cures. This creates a nice "Bobble-Head" effect.

Step 11: Write Your Message:

If you're anal or just like to make life easier for yourself, you should probably do this step before you attach the solar panel.

I used a semi-fine point silver paint pen. Leave most of the solar panel exposed so the batteries can charge.

Step 12: Start the Invasion:

Box these up and give them away. I packaged mine a couple of days before Christmas and they were still blinking when they were unwrapped.

You can play with the resistor value to determine how sensitive the solar panel is. With the 1M resistor it has to be pretty dark before the LED starts blinking. With a 100k resistor it will blink in a lit room but turn off in direct sunlight. It all depends on how sneaky you want your robot to be.