Why not give that loved one something special. A fabulously unrealistic beating heart.
OK. I seem to have a thing for building Rube Goldberg like devices that are overly complicated and do so little. This is one of those.
I'll prob be modifying this as I go, and can already think of things I should be doing different. I will say that the girlfriend actually squealed a little when she saw the completed first version. The cat can't get enough, and will shortly be destroying it I'm sure.
The whole concept is based on general magnetic principals and re-using junk. I have actually used this idea once before to make fluttering mosquito wings. I very well may make another at some point. I'll post if I do...
1 Altoids tin, or suitable container.
1 old or dead CD Rom drive. Desktop style preferred, although a laptop drive would work.
1 555 timer chip.
1 47uf capacitor
1 3906 transistor
2 3.3K resistors
1 1k resistor
1 red LED
Power source - 3-6 volts. This could be a wall-wart, hacked USB cable, AA batteries, whatever.
Wire of various sorts
wire snips, the finer the better
screw drivers, various sizes. You need at least one large straight tip, and 1 large and 1 small Phillips. The small should be a jewelers size, or so.
possibly a magnifying glass, or reading glasses, depending on your ability to see really small stuff
A good deal of patience
I'm assembling this one "free form" which means that I will not be using a board of any kind. Mostly cause I didn't have any handy. This can certainly be laid out any way you want.
Step 1: CD Rom Tear Down
OK. First things first. We need to claim the parts we need from the CD Rom drive. Yes.. I know it's a DVD Rom drive in the pictures. Lets not be picky.... Start taking out screws. After some prying and swearing you should get down to the point where you will see our target, the laser eye assembly at the center. This will become the part that does the actual mechanical "heart beat" work.
Usually, it's a floating assembly riding on two rails. this can vary by manufacturer. If you can get the two rails free, it usually slides right off. Be careful to disconnect the ribbon cables. If you cut them, leave some slack, just in case.
Once you have the main laser assembly free, start removing external parts until you get down to just the laser focusing assembly. This will be where the small Phillips head screwdriver comes in handy. It will be the part with the laser eye suspended between two magnets with some small coils. The coils are energized to move the eye around and provide fine focusing during CD read operations. Check the pictures, it will make more sense.
Be VERY careful to preserve the connections on the focusing assembly. ripping the ribbon cable off the eye makes it nearly impossible to solder the wires to it later.
There are a lot of other goodies inside the remains of the CD Rom drive. take a minute to poke around and see what else you can scavenge. LEDs, motors and such.
Step 2: The 555 Timer Circuit
OK, we have our mechanical part. Now we need something to drive it. The 555 is a really nice little workhorse of a chip. We are going to use it to create the pulses that will simulate a heart beat.
The 555 is designed to put out a timed pulse depending on the values of the resistors and capacitor attached to it. I played around a little and eventually decided on a 47uf capacitor, and two 3.3k resistors. This gives a nice beat, slightly faster than a normal human heart.
The diagram below explains how to lay it out. I had to use the 3906 transistor on the output, as the pulse from the chip is just not strong enough.
If the diagram below is Greek to you, I would encourage you to check out these sites. They have some fantastic information to get you started:
You can see that once you have it together, it looks easier than it appears. These are the basic steps I use:
1. Connect Pins 4 and 8. If you are free forming this, you can bend the pins under the body.
2. Connect pins 6 and 2. I usualy run a jumper over the top of the chip to avoid bending the legs off.
3. Solder the capacitor across pins 1 and 2, with the negative side on pin 1.
4. Solder one of the 3.3k resistors across pins 7 and 8
5. Solder the other 3.3k resistor across pins 6 and 7.
6. solder the negative power lead to pin 1
7. solder the positive lead to pin 8.
I would apply power at this point and check to make sure I am getting a pulse by putting an LED across pins 3 and 1, with the positive lead on pin 3. If the chip heats up at all, something is connected wrong. If you have a nice pulse, then: (with the 3906 in "dead bug" mode, flat side up, pins facing you)
8. solder the middle leg of the 3906 to pin 3.
9. Solder the left leg to ground (pin 1)
Now, you need to connect the "eye" to the circuit. There will be 4-6 connections on the eye. take a battery or power supply and test the contacts to see which ones make the coil jump up. some contacts will make is slide to the side, some up, some down. you will get the idea. When you have the right ones...
10. solder the right leg to one of the connections on the coil from the CD Rom drive
11. Solder a connection from the other connection on the coil to the + source (pin 8 or 4)
I find it's not generally needed to solder pin 5 of the 555 to anything. it just works.
Now, when you connect the power, you should see the "eye" jump up and down. If not, check your connections. The biggest mistake I usually make is connecting the 3906 backwards.
Step 3: Doctor, the Paitent Has a Pulse...
A: You call an hambulance!
We are in the hone stretch now. We have a working timer, and a working "thumper" for our heart. I took the working assembly and glued it to the inside of a Altoids tin. I then glued a small coil of wire on the top of the eye, making sure it would not hit the top of the tin when the eye extended.
At the last minute, I added a red LED to the circuit. I just connected it and the resistor to the positive and negative power-in. nothing fancy. Just as shown.
I drilled a small hole in the top of the tin directly over where the eye is. when the tin is closed, I drop a piece of wire through, when the eye jumps, it will push this wire (or "push rod")up and down.
I then made a small loop in the top of push rod so I can glue it to one end of the heart. I closed the cover, and cut a heart from paper. I glued the bottom tip of the heart to the top of the tin, then glued the loop on the wire to the top of the heart. Look at the pictures. you will get the idea.
I would post video.. but I can't find the charger for my camera. maybe at some point...
That's it.. Have fun. As usual, there will be a torrent of people who have more ideas. Bring it on! and lets see the pictures when your done.