This is the Valentine’s Day gift project I created for my wife this year. It was inspired by this Valentine Lightbulb project which my wife found via Pinterest. She also created a gift based on this same project as part of her 24 Hours of Love (1:14AM), however we didn’t plan to both create gifts based on this…I guess I stole the idea since she was the one who found it first… We took similar but different approaches – I’ve taken more of an engineering approach to it versus her more artistic approach. She knows I love LEDs and switches so her box incorporated those features – I love the clicky-ness of the switch and the way the hearts catch the light. She also went all steampunk with it and took an otherwise plain unfinished box and made it look antique. She’s awesome like that 🙂 For my implementation, when I saw the lightbulb project I immediately wanted to replace the wire hearts with electroluminescent (EL) wire to simulate a bulb filament. Then, for the message, I didn’t want it to just be written out on paper – I wanted it to light up as well.
The Valentine Love Light was built in two parts – the lightbulb itself with the EL wire heart “filament” and the base enclosure with the illuminated “i love u” message and the lightbulb screw mount. The electronics are battery powered and operated by a push-on-push-off switch on the back of the enclosure.
I really wanted to make the bulb it’s own entity and have it look and feel like a real lightbulb. The filament and glass stem were first removed from an incandescent bulb. Any sharp edges on the inner diameter were filed down before adding the EL wire heart. Thin (1.2mm) “angel hair” white wire was used because I wanted it to simulate the thin filament as close as possible and because the thin wire holds its shape when you form it. After forming it and attaching wires to it, I placed heat shrink over it to simulate the stem. The bottom contact from the screw base of a CFL light was removed and used as the bottom contact for the bulb. The other connection to the EL wire comes out of the side of the heat shrink and gets attached to the screw part of the base. I learned quickly that the metal used for the screw on the bulbs I chose would not take a solder connection. To overcome this, I pressed a strip of copper tape around the inside of the screw base. The other connection to the EL wire was then soldered to that copper tape to make the electrical connection. Once the heart was inside the bulb and the side connection made, I used epoxy putty to seal up the bottom and keep everything in place. A black rubber washer was used to keep the epoxy from going into the bulb area as I pressed everything in place.
The base enclosure is a CU-234 from Bud Industries. This size seemed about right for the size of bulb I’m using and I happened to have some on hand. I had first evaluated some other light bulb screw bases (the kind that mount directly to electrical boxes like in an attic) but they were all too large for the box and I wanted to keep this more compact. A couple aisles over in the local hardware store I found what I needed: a threaded ceramic lamp socket. It comes with one ring nut and I picked up some extra so I could use those to hold it in place through the box. For a power switch, a simple push-on-push-off style was selected for power and is mounted bottom center on the back side of the box.
Now the hard part – the illuminated message. I mentioned this project to a friend and he offered the services of his family’s machine shop. This was great because I had no idea how I’d be able to cut out the letters by hand without it looking terrible. I provided them with a CAD drawing showing the position and sizes of the holes and the dimensions of the message. They couldn’t cut the text directly because their machine didn’t support the font I chose (Helvetica, of course). Instead, they scanned in a print of the drawing and had the machine simply cut the outside of the stencil. By using a 0.040″ bit they were able to get really precise cuts. As you can see from the results, their machine is awesome and I was amazed at how it turned out. The surface was sandblasted to help prepare it for painting.
The box was spray painted first in white and then with a clear coat to make it shiny and to protect the paint. I guess it matches my white Apple products now 😉 The letters were filled with a clear two-part epoxy that was dyed with red resin dye that I found at our local craft store. I placed a sheet of diffusing plastic behind the letters to help spread out any hot spots from the light sources within the box. I used 5 Cree 5mm white LEDs (1 for “i”, 3 for “love” and 1 for “u”) to light up the message. To hold the LEDs and to create separate lighting regions, I turned to my old structural standby: LEGO. I guess it’s a coincidence (or not) that a previous project using EL wire also used LEGO bricks. I just have lots of them and you can build just about anything. The white bricks reflect the light back through the diffused plastic and makes the lettering glow a nice pinkish-red.
For the electronics, I really only had to do two things: 1. provide DC power to the LEDs and 2. supply high-frequency AC power to the EL wire. For the latter, I used the same EL wire inverter I used on my Jacob’s Ladder project. I could have just wired everything to a battery pack via the switch and be done with it. However, I wanted it to be more dynamic. I wanted the message to light up one word at a time and I wanted the heart in the bulb to “beat” or fade in and out. I knew it would be no sweat for a microcontroller-based circuit. For the letters, I would connect the LEDs to PWM outputs and vary the duty cycle to adjust the brightness to fade them in or out. I want to do the same fading effect for the EL wire, but controlling the high-frequency/high-voltage AC is a bit trickier. I used an optocoupler/triac combination like on Sparkfun’s EL Sequencer and also connected the LED in the optocoupler to a PWM output. Some simple code is all that would be necessary to do the fades upon power up.
I had most of the components on hand in breadboard-friendly packages so I was able to easily prototype the circuit, mainly to prove out the EL wire control. The white LEDs are driven with N-channel MOSFETs so they are supplied with their rated current without exceeding what typical microcontroller ports can supply. As far as the microcontroller is concerned, I wanted to stick with what I know so well – the Arduino platform, specifically the IDE. However, I knew I didn’t need all the features and size of a full ATmega part like those found on the Uno or similar. I had some ATtinys on hand so I decided to try those out. I had previously avoided them because I either needed more program space/pins or because I didn’t want to go through the trouble (not that it’s a lot of trouble, really) of programming it via ISP. It’s just that using a serial bootloader with the Arduino IDE is so much nicer. Then I found a cool ATtiny Arduino Core project on GitHub that included bootloader support. Using their code, I was able to flash a bootloader on the chip (ATtiny84) and connect to my USB-to-serial converter via software serial. In essence, I had a 14-pin Arduino-compatible device (for the most part – some functions are not there and it has less code space but still plenty for what I’m doing). Even though all the parts could have been placed on a bread board or simple through-hole prototyping board, I decided to make a simple PCB since it is so inexpensive and easy to create PCBs with services like OSHPark now. This helped keep things organized anyway, component-wise. The PCB also serves as a nice development platform for the ATtiny84 with focus on LEDs and the high-voltage triac switching for EL wire (could also be used with mains power if you are careful). I will create a separate page documenting the PCB design for reference.
To complete the build, I connected the PCB and the inverter to the battery pack and switch and secured everything with double-sided foam tape. A 3xAA battery pack was chosen because it provides a nominal 4.5V supply which is perfect for the inverter and the 3.2V LEDs. The ATtiny84 can work down to below 3V so I should be able to use the full energy capacity of the cells (discharge down to ~ 3V) while maintaining most of the brightness of the LEDs and EL wire.
The whole thing turned out really well and my wife loved it. It creates a nice soft glow at night. I had a lot of fun making this and it’s a way for me to tell her “i love u” even when I’m not around.