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I didn't know what to call this instructable, "robot night light" "glow in the dark sign" "back lit laser engraving" "poor man's neon sign" all came to mind, but this could be used for advertising, emergency exit sign, an award or it could just to sit on your desk and look pretty. The size is only limited to the size of the laser cutter you have. This one runs of a battery, but you can run it from a plug pack, up to 12volts if it is going to be run all the time. As with most things that produce light it is very difficult to take a photo that does it justice, even in the daylight it looks really good, and in a darken room it lights up a part of the room. I spent more time taking photos than actually building it sadly this is the best I could do. It may be too bright for a kids night light. I made 2 versions of the sign the blinking "neon type" sign and the standard glow in the dark sign.
Step 1: Stuff you will need
To make a basic glow in the dark sign you will need.
Step 2: Making the wooden base (glow in the dark sign)
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I cut a nice piece of timber 120mm long, and cut a slot in the bottom 1 inch (about 25- 26mm) wide and and about 17mm deep, you may wonder why I sometimes use mm and inches in my projects its because I live in a metric country but quite often I use parts that have been made using inches, like the 9 volt battery which exactly one inch wide, which is much easier to read on a ruler than 25.4 mm.
The slot was cut on a bench saw and the waste cut out with a chisel. A 9mm slot 10mm deep was cut on the top side as the ribbon is 9mm wide. 2 pieces of 3mm thick acrylic were cut as spaces to locate and support the sign, and these are fitted on top of the ribbon.
After test fitting everything and soldering the battery snap on the 2 smaller blocks can be glued in. The base was sanded up and given a coat of furniture oil.
Step 3: Making the laser cut base (blinking sign)
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The base for the blinking sign was designed on Prodesktop and cut out with the laser cutter. the only really important measurements are the gap to fit the 2 ribbons, the 2 signs and the 3 spaces. The dxf file is below, if you want to cut out a base that is the same, you must use 3 mm material.
Once the base is glued together the ribbons can have wires soldered to them, the adhesive backing removed and placed in the base.There is some overlap in the middle, as the ribbons are 9 mm wide and the space is only 15mm.
laser cut dxf.dxf34 KB
Step 4: Wiring up the ribbons
To wire up the glow in the dark sign, its just a case of soldering a battery snap to the ribbon. The ribbon that I bought has a weather proof coating, which has to be removed so that the LEDs touch the acrylic sheet, so you can get to the pads that need to be soldered. A quick look on google and I found that not all ribbons have this coating. The pads have to be scratched with a knife to remove the coating or the solder will not stick. LEDs are polarity sensitive and can be damaged if wire the wrong way around. So make sure the red wire goes to the + sign on the ribbon. I found they work fine on a 9 volt battery, but 12 volts will make the sign even brighter.
The blinking sign has a flip flop circuit driving the 2 ribbons. Flip flops are a pretty common circuit and there is lots of info on the net about them, you can buy them as a kit or make your own with a few cents worth of parts. there is even an instructable on how to build one here. http://www.instructables.com/id/Flip-flop-LED-circuit/
Just wire in the ribbons where the 2 LEDs would normally go. The kit that I got has pots which allow you to adjust the blink rate.
A word of warning about plug packs there are 2 types, regulated and unregulated. Just because an unregulated plug pack says its output is 12 volts, doesn't mean you will get 12 volts out of it, unless it is connected to the correct load the output could be double that, frying your flip-flop, and LEDs. Go for a regulated plug pack, its output voltage will be more stable regardless of the load.
Step 5: Engraving the sign
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The Laser cutter I have access to is a cheap Chinese rabbit laser, and has its limitations, one of them being you can't cut and engrave on the same drawing, so it is quite difficult to get the engraving in the centre of the cut. I found that most images can be imported straight into the laser cutters software and it would do a reasonable job, but to much detail at the bottom of the sign will interfere with the light causing dark spots above it. So I remove the Instuctables text from below the robot and this gave a much better result.
This was removed with Gimp, which is a free, photo editing software Linux, Macs and Windows.
Engraving takes a long time with a laser cutter as the gantry whizzes back and forth across the material not unlike a printer, so the robot took around 1/2 an hour to engrave.
With the text I drew it in pro desktop, and exported it as a dxf file which will be recognized as something to cut by the laser, I then turned the cut speed up, and the power level down, so that the text would only be cut part way through the plastic. This means that the text can be engraved in around 30 seconds.
Some interesting effects can be made by playing with the focus of the laser as well as the power levels, Moving the material closer to the lasers lens gave a ghosting effect, while further away gave a wide line effect.
I also found that the engraving is slightly better when viewed from the back side, so I mirrored the text and the robot.
sign blank.dxf17 KB
sign share make.dxf425 KB
Step 6: Other stuff
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If you just wanted to make a sign without the glowing part, I found that painting the engraving with spray paint and wiping off the excess with a paper towel, soaked in meths worked very well. I made a spelling bee award this way and it worked very well.
I am also planing to make a blinking sign with coloured LEDs an clear acrylic, which I think could possibly work better than the coloured plastic, and white LEDs
Come to think of it there is no reason I could have 3, 4 or even more layers to the sign and run it off a micro controller, and have some real animation happening.