This is a fun project that can be built in a couple of hours (minus the glue's drying time).

Building a step stool is a simple project. The circuit is also extremely simple but it can be used to drive robot motors, water pumps, or high voltage lights from a Raspberry Pi or Arduino.

Parts

Step 1: Cut the Top and Legs

Here are the rough dimensions of the wood. I didn't do any pre-planning for this project, so I don't have any templates. These measurements were taken after the project was finished.

The only measurement that's important is the ratio of the top platform to the base. Make the base about an inch longer and wider than the top so it won't tip over. Start this project by deciding how big you want the top then cut the legs accordingly.

My top was 12" by 7"
The total height was 7"
The width of the bottom of the leg was 8"
The legs were splayed out at a 10-degree angle.

I free-handed the leg shape on one edge then cut it out. I used the scrap from that cut as the template for the other edges of the legs.

When you cut the mortise in the legs make sure you take the 10-degree angle into consideration. Cut a normal rectangular mortise, but stay away from the bottom edge. After you've cut the mortise, use a chisel to cut the angle. If you mess up, the overlap on the tenon will hide some mistakes, so don't worry too much about it.

Step 2: Cut the Cross Beams

The center cross beam is made from three parts, the center beam, and two pieces that are attached to either side of the center beam.

Carve out the middle of the center beam and cut tenons on the ends.

Use the center cross beam as a pattern for the other two. Cut a mortise in these, but don't cut all the way through. When the three pieces are placed together, there should be a hollow center.

Step 3: Assemble the Step Stool

Glue all the joints and clamp everything. Only glue one side of the center beam. The other side will be the access panel used to install the electronics and change the batteries.

After the glue dries, apply whatever finish you want. I don't really like stains, so I just used a simple oil finish.

Step 4: Attach Magnets to the Access Panel

Drill small recesses on the inside of the center cross beam and the cross beam that will be the access panel.

Put some epoxy in the holes and insert the magnets.

Step 5: Install the Circuit

Attach the LED strip to the center cross beam. Drill a small hole at one end large enough for a red and black wire. Solder the wires to the led strip and cover the exposed solder with hot glue.

Measure the diameter of the PIR sensor and drill a hole through the center of the cross beam covers. Screw or hot glue the sensors in place.

Solder the parts together as shown in this diagram