This instructable covers how to convert your baby swing to wall power, so you can just plug it in and not have to change the batteries.
It's designed so that you can choose wall power or batteries, depending on your needs.
This Instructable requires soldering--There are other instructables covering that if you need help learning.
Step 1: Tools & Parts Necessary
Screwdriver(s)--Used to open up the motor/switch/battery housing
Wire Stripper/Cutter--Used to cut and strip the old and new wiring
Soldering Iron--Used to solder the new switch and wires to the existing wiring
Heat gun or Cigarette Lighter--Used to melt the heatshrink tubing
5 VDC Power Supply--I used an old cellphone charger. It needs to have a similar voltage output to the batteries in your swing. Count the batteries in your swing. Each one puts out 1.2VDC (Whether AA, C, D, ect). Obviously 9V batteries are a different animal. Mine used 4 "D" batteries, so I needed at least a 4.8VDC power supply.
Double Pole Double Throw (DPDT) Switch--A small one from Raido Shack, etc. is fine.
Solder--Used to secure the new wiring
Heatshrink Tubing--Used to protect the solder joints
Epoxy or Super Glue--Used to secure the switch to the housing
Step 2: Disassemble the Swing
I had to remove about 10 screws in order to accomplish this. The picture shows the plastic housing split apart, and the battery box, and wiring visible.
There should be two wires leading from the battery box, a red wire and a black wire. This is the positive (red) and negative (black) power for the motor/sounds/etc.
Cut both of these wires. I chose to cut them equally distant from the battery box and the circuit cards for the motor. This gave me several inches of wire to hold onto when soldering, which is very helpful.
Step 3: Build Up the Switch
The center two positions will be connected to the motor side wiring in the swing. One side of the switch contacts will go to the battery box wiring, and the other side will go to the new power supply.
The positive wires should be on one side of the switch (left or right), and the negative wires should be on the other side.
It does not matter which side goes to what power source, as long as the middle contacts go to the motor.
Step 4: Cut Hole in Housing for Switch
I chose to drill the corners of the area with a small drill bit and then use a razor blade (multiple passes) to cut between the holes to make my rectangular cutout. I cheated and used my Dremel tool a bit, but the razor blade method works fine as well.
Step 5: Prepare Power Supply
Cut the cell phone connector end off, and strip back about 3/8" of the insulation to expose the copper wire.
Carefully separate the stripped ends and plug the charger into the wall. Using your multimeter, touch the red lead of your meter to one wire, and the black lead of the meter to the other wire. If the meter displays the correct voltage of the power supply (say 5.0 volts), then mark the wire the red probe is touching as the positive wire. I used masking tape to do this. If your meter says (-5.0 volts), then the wire the black lead is touching is the positive lead. Mark it as such.
You will need to figure out how to run the power supply wires through the plastic housing of the swing in order to connect them to the switch. I chose to drill a hole on the bottom of the swing, near the battery box. Drill a hole just large enough to fit the wires through. The tie a simple knot (overhand) in the power supply wiring on the inside of the housing to provide strain relief for the wiring. You DO NOT want the solder joint to be pulled on when someone trips over the wiring, etc.
Step 6: Connect the Wiring
Be sure to slide heatshrink tubing on the wires and push it away from the joints prior to soldering them. Once the joint has been soldered and is cool, slide the heatshrink tubing over the joint and shrink it with your heat gun/lighter.
Push the switch through the hole you've created and connect the switch wires to the appropriate wires--battery box, power supply, and motor.
I stripped the wires back about 1/2" inch and then "hooked" them together. (see picture). Basically I bent the stripped ends into a "U" shape and connected the "U"'s together. I then soldered them together. Note the white heatshrink tubing on the red wire. Once the joint is soldered, that will be pulled down and shrinked over the joint.
You will need to do this for all six wires.
Step 7: Reassemble and Test
Place the batteries in the unit, and plug the power supply into the wall.
Turn on the swing (with the switch in either position) and see if it works normally. Push the new switch the other direction and make sure it works normally.
I then glued the switch into the housing using epoxy (in the first picture it's under the masking tape, being held in place while the epoxy cures).
You can unplug the power supply and then determine which direction the switch has to be in for the power supply to power the swing motor.
Label the switch accordingly.
Enjoy not having to buy batteries!