I started building this toy because I was finished with my son’s Halloween ride. You can find that instructable here (https://www.instructables.com/id/Halloween-Firetruck/). I periodically go to the dollar stores to find inexpensive travel toys or components for projects. On a recent trip I found the T-Rex toy which was used in this project. I believe it costs in the $1-2 range. My son has many dinosaurs already so I thought I could make this one a little more interesting for him.
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Step 1: Parts and the First Incision
Although you can see a purchased and unused battery in the photo, I did not use it in this build (had it in reserve in case I needed a third battery for the LEDs). With that the only parts used which were purchased were the dinosaur and the LEDs used for his eyes (and of course the glues holding it together). The button, batteries and wiring were all taken from an old computer and musical birthday card. A rough estimate of cost to build is $2.12 for the dinosaur and LEDs.
The first step for this project is to cut the dinosaur open. This one was very simple as there was a seam in the mid section where it was glued together. Using an xacto knife I carefully cut at the seam until it was fully separated. This is the part where it's easy to slip and cut yourself so be careful. This is also the point where you DO NOT allow your child to see the mutilated toy, they will throw a complete fit (at least my son did).
Step 2: LEDs
I took two LEDs and cut off the positive and negative leads leaving about a quarter inch on each. Using some old electronics wire which was salvaged from a very old desktop computer (or perhaps printer I forget exactly what machine it came from) I cut four pieces of equal length (around 3-4 inches which ended up being much more than I needed). The cable was far too thin for me to easily strip (I tried a few times but with minimal success), so I did the next best thing. Using a lighter I burned off the ends so perhaps 1/16-1/8 of an inch of wire was showing on each end. I solder one cable to the positive and negative leads of both LEDs. Testing is a very essential step at this point so grab your batteries and just make sure that the wires on the LED end aren't touching. If the LED lights up you're doing well, suggestion, use different color cable for positive and negative to make life easier. Next take a small piece of electrical tape. Put one end in-between the leads and then wrap it around both leads, this way they can't touch anything they're not supposed, or each other.
Grab a power drill and carefully, and slowly, drill out each eye with a bit big enough for the LED to fit snugly through. There isn't a lot of space so a pair of needle nose pliers are useful here. Slide the cables for the LEDs in through the eye socket (one LED per hole) one at a time and grab the cable with the needle nose pliers pulling them out through the mid-center of the toy. Don't pull to hard, you may damage the soldering or cable. Push the LED snug into the socket and if you'd like some extra security super glue them into place. This is a very simple electrical setup (no alternating eye flashing or various combinations) it is best to twist the two negative cables ends and two positive cables ends together. Give them a small amount of solder so that they hold together (twisting never holds together long term with thin cabling I have found).
Step 3: The Button
The button is an old computer power button, it does not toggle and only works when you are actively pushing it. So I soldered some new cables to the leads on the button and tested it using a multimeter. Next I drilled a hole big enough for the button to go through. This now gets into the reason I used this button versus a smaller one. The length of the push part is nice a long allowing the button to be mounted inside of the dinosaur but can be pressed from the outside. There is about an 1/8 of an inch material on the belly so my only alternative would have been a switch if the button had not worked (or grind down the material, but that would have been too much for a small project like this).
One of the pushbutton cables was soldered to the positive cables to the LEDs. I now did a strange little "hack" for the battery connections. I had an old broken ironing board in the basement. Using a Dremel and metal cutter attachment I cut one of the steel rods from the board and cut two very small "cookies". I then soldered the negative LED cables to one of the "cookies" and the unconnected pushbutton cable to the other. These small pieces of steel rod have a nice solid connection the batteries when I do a quick integration test.
To put the button in the dinosaur I used hot glue. This was tricky but fun. To start i put the button in place inside the dinosaur body and then applied hot glue on three sides. Then using a finger I held it into place until the hot glue was pretty solid. If you don't do this the connection will be weak, which is what I did and had to re-apply. I also put some hot glue on a popsicle stick and then whipped it on the far side (the fourth size i couldn't reach with the glue gun). The final result should allow you to push the button without the button moving very much if at all inside of the dinosaur body.
Step 4: The Battery
So I wanted to hold the batteries in place and since I don't have a real battery holder for the two 303 sized batteries I have on hand I decided to use some spare tubing I used in another project. I cut a very small piece and slide it length wise. From here I could slide both batteries in and they would stay together. Using the steel "cookie" connectors I tape the battery and connectors together and when I pushed the button the LED immediately illuminated SUCCESS.
Step 5: Final Assembly
So I don't have photos of videos of this last part, but I can describe it. I carefully slide the battery holder (with batteries, connectors and all taped up) into the body of the dinosaur. Once that's done you slide in the cables into both the front and back of the dinosaur, being careful to not yank on any cable too hard and break a solder connection. Now grab the ever useful super glue! Use the super glue to reseal the seam which you originally cut the dinosaur open with and hold for about 30 seconds. YOU'RE DONE.
Now of course I always worry that my son will not like my creation. It has happened a few times, but luckily all of the toys and creations I display here have been very successful with him. This toy to date (it's been two days) he will rarely put down and does not allow my wife or myself to touch it. So I am very happy to have a successful end result.
This is the simplest build I have put up here. Let me know what you think.