Lightboxes are one of those ridiculously priced items that at the same time they are so easy to make, and thats one reason instructables is full of such projects.
There are also many ways to make them, so there are many approaches to the end goal. Here we will try to exaplain ours. Our main goals, was making it as cheap as possible and at the same time re-using as much old material as we could.
Materials and Choices
Before I started writing this instructables I searched to see what other people have done, and of course we are not the first to think of using an old tft screen for our project. A TFT screen is in essence a lightbox with a tft board in the front. So removing the board (and a few polarizing sheets) will leave you with the lightbox.
Here is a similar attempt. The advantages of TFT screens are numerous:
a) it already has an acrylic sheet and reflecting surface. And not only that, the acrylic sheet is dotted in such a way, as to distribute the light more evenly across the board.
b) it already has a frame and the electronics needed to power it up.
c) people throw them away all the time
The problems of TFT screens are fewer
a) it needs some hacking to let the screen constantly on
b) it needs a power plug (not portable)
c) many thrown away tft screens suffer from burned CCFL lights (or boards).
Thats why even though we decided to use the screen and the screen frame, we opted for using LEDs instead of the original electronics. CCFL are also not so portable (ie battery) friendly.
There are also LED lightbox instructables around. Like this one or this one. We opted for smd LEDs in order to make our design more compact and at the same time operatable from one (recycled of course from old laptops) 18650 Li-ion battery (3.7V).
SMD LEDs are a pain in the ass to solder, so I strongly suggest using the 3528 Variety (like here). They are very cheap and at the same time big enough to solder without cursing. We used way smaller ones just because we had them around from some old broken LED TFT screen, but we suggest you go the 3528 way :)
We decided against SMD LED strips, as most of them have to be operated at 12V and the 12V ones use resistors which "burn" power, making them not so efficient. If you really dont want to solder SMD LEDs, you can use an SMD 12V strip and a XL6009 step up converter (like here), to convert the 3.7V of the li-ion battery to 12V. This is a less efficient design than the one we used, but it spares you the smd led soldering part.
One could ask why didnt we use 3 li-ion batteries in series (so that we would reach close to 12V). The main problem is the charging circuit. We also opted for a very cheap USB powered li-ion charging circuit and protection board costing half a euro (like the one here) which charges only one in series battery.
So all in all our total costs were not much more than 5euros and at the same time we had materials for more lightboxes if needed :)
Of course your cost may vary, depending on how much you scavenge from old equipment, but even buying the LEDs or LED strips wont cost you more than 10-15euros in total.
So here are the steps as we did.
Step 1: Disassemble the Tft and Throw Away the Un-needed Parts
Disassembling the TFT is quite straight forward. If it's not for you please follow the nice instructions provided in this instructable.
What we need from the TFT screen, is the dotted acrylic sheet, the metal frame, and the white reflecting sheet on the bottom. And thats more or less it.
When disassembling please give extra care no to break the ccfl, as they contain mercury.
Step 2: Gluing and Soldering the LEDs
I will assume that you use 3528 LEDs. the ones you see in the picture are quite smaller so your life will be easier.
First check how many LEDs you need. We will use a AMC7135 chip which provides 350mA of constant power. Each 3528LED can be safely used with 20-25mA so by using 14 of them we will provide 350mA / 14 = 25mA to each. If you feel like using more and driving them softer you can go with 18LEDs which means each will receive nearly 20mA.
at 20-25mA no extra cooling is needed.
We would like to mount them on the same place where the CCFL were placed. The dotted acrylic sheet from the TFT, is dotted in such a way as to provide a uniform light from the directions the CCFL were mounted.
In order to mount each LED we used a tiny drop of super glue. Space them equally over the length of the acrylic panel and glue them in place. This will make the soldering job waaaay easier. But before you mess with the superglue, make sure you know the polarity of the LEDs.
there are many ways to check polarity. LEDs are diodes and only work one way. The one we used is the diode function of our multimeter. When you touch the LED leads the correct way, the LED produces a dim light. If your multimeter doesnt do that, you will need a 3V source, ie a power supply, a pill battery (like the one the computer motherboards have), or 2AA batteries connected in series. Just touch the LED leads one way or the other with the 3V source, and when they turn on (even dimmly) you have found the correct polarity.
You will want to mount them with the same polarity on the same side. So first check the polarity of the LEDs and then glue them with all the pluses or the minuses on the same side. This will make the soldering job quite much easier, as we will mount those LEDs in parallel (ie all the + soldered together and all the - also together).
So glue them one by one, apply some pressure for the Cyano acrylic glue to stick and go on.
Next step is cutting even length wires. Choose two colors so you can tell plus from minus and make sure they are not much shorter or longer than the space between the LEDs. You can temporarily keep them in place by using masking tape and then SOLDERING :)
On each LED lead you will need to solder 2 wires together. Be quick with the soldering gun as the LEDs are small and if you wait too long they will burn. If you seem not to manage a joint and the seconds are ticking, stop the effort let the led cool down and continue. But also, Burning a couple of the LEDs is not such a hassle. as you can cut them and glue new ones. Scrape them of the acrylic with a knife or a dremel and glue a new one.
On the last LED of each side, solder bigger wires as we will need them
After you solder all the LEDs check for bad connections (check that all LEDs work). You can do that safely by providing 3V to the wires you just soldered (the correct polarity please). 3V are the big "pill" batteries if you dont have a regulated power supply around you.
This part of the job takes around an hour or two depending on your skill and frustration.
If you chose to go the LED strip way, just glue the LEDs on the acrylic panel, and then connect the output of the XL6009 step-up converter on the end of it. By adjusting the output power (from around 10V to 13V), you can adjust the brighness of the LEDs (because two strips of LEDs could be TOO bright for your needs). We dont have photos for that but its a quite straight forward experience (and more hassle free).
Step 3: Soldering the Control, the Battery and the Charger.
The AMC7135 chip is pretty straight forward to use. As you can see in the datasheet, it has 3 pins. As we look it from the front side (the side where the letters are), the middle pin is connected to the ground, the right pin is connected to the plus of the battery and the plus of the LEDs and the left pin (out pin) is connected to the minus of the LEDs.
glueing the ΑΜC7135 upside down on the acrylic with superglue makes your life easier. Be careful that when you glue it upside down the pins are also mirrored :)
so with the AMC7135 soldered you can safely now use your LEDs from 3.2V up until 6V. The AMC7135 will make sure it provides a stable current of 350mA on the LEDs.
The lightboard is pretty much ready. Now we need to connect the batteries, the charger for the batteries and an on/off switch. The photos we provide use a bit of a different topology, as we used a circuit with low battery indication, but if you use the charger with the protection circuit, the low bat circuit is not necessary.
We found flat li-ion batteries from an old apple somebody threw away, but any 18650 Li-Ion battery can do. You can also solder more 18650 batteries in parallel if you want more capacity. Old 18650 batteries are perfect for this project as even 3x 18650 in parallel that only have a 600mAh each, will give you more than 5 hours of continuous usage before you will need re-charging them.
Solder all batteries in parallel and then solder their two leads on the B+ and B- of the charging board. This way you can USB charge your batteries when needed. Then Solder two wires on the OUT+ and OUT- of the charging board. Connect the OUT- on the GND pin of the AMC7135 and connect the OUT+ on the middle pin of a 3way switch. Then connect the Input + pin from the AMC7135 on one of the other two pins of the switch. This way you also control on/off on the LEDs.
Step 4: Questions Etc
If you feel that the guide takes for granted some steps please feel free to ask.
We also post the 3d printed parts on thingiverse and put a link here for those who want to use them