A Star is Born

An LED Christmas star that is.

What Went OK ?

Following on from my previous post on christmas lights for 2016 this update should detail what I actually made. I wanted to make a light framework to mount the LED strips onto and found a bag full of old fibreglass tent poles – ideal as they are strong and lightweight. I made a hub from two discs of plywood glued together and then drilled 8x holes onto the sides for the poles.

I added some car body filler to strengthen the joints and to waterproof the plywood. The hubs were primed grey and then painted with some black gloss paint.

The WS2812 RGB LEDs came as a panel from Ebay. I had to break them apart and solder individual wires between them. I made a simple jig to hold the LEDs face down (small drill holes and a blob of Bluetack). Each of the 8 arms required a strip of 10x LEDs….each strip required 27x small pieces of wire….each cut, bared back, tinned and soldered into place. I soon doubted my I had decided to do this.

After about 5 out of the 8 strips I was managing to get the process down to about 30 minutes per strip.

Once I had all eight strips I tested them (and corrected a few soldering bridges). By now I had decided against the tubing method of protecting the lights from rain – the PVC tube was quite expensive and I wasn’t sure how I’d manage to pull the strip into place. I decided to mount the strips to the frame and use silicone sealant to waterproof the whole unit.

I put generous blobs of clear sealant on the back of each LED on a single strip and then used 100mmx2.5mm cable ties to secure the strip to one of the frame’s arms. I then added more silicone around the LED to protect the wiring and the WS2812 LED. I had also planned to glue small pieces of 10mm hot melt glue stick to each LED to act as a diffuser – but I trialed out a spare WS2812 and a blob of clear silicone. That worked really well so I added a nice silicone ‘iced gem’ to the top of each LED (see below if you don’t know what an Iced Gem is). 2p3dh3c

Nearly there now, I took a short video of a single starburst unit which you can watch here on my Youtube uploads.

I printed off my PCB design this morning at my local library – they have a well maintained laser printer and charge me 10p a sheet. The design is currently drying after being rubbed with vegetable oil ! I’ll try to expand on that in my next post.

starburst_pcb

I’ve got some electrical boxes; sanded them lightly and painted them black to hold the PCB. The whole unit should be self-contained and require just 5v to operate.

What Went Wrong ?

After sealing the WS2812 and any bare wires with clear silicone I let that dry. I then found some black silicone and thought I’d give it a second coat for added robustness. A few hours later and the black hadn’t dried….maybe it was the damp/cold evening drawing in so I brought the star inside last night. This morning – the black silicone was still uncured.

Now I had a dilemma on what to do – scrap the black silicone off ? Use a solvent to remove all traces ? That could damage the PVC cables, the clear silicone ? Use something to ‘set’ the black silicone ? Below is a test card where I tried out various household chemicals on a sample of the black silicone to see what dissolved it or made it cure. Hours later they were all fairly similar and still gungy.

img_20161029_182754072

So onto plan B, I daubed more clear silicone over the black, wiped it around and hopefully when that has set it will encase the bad layer. Seems OK at the moment.

Lesson learnt – old silicone can also go bad even if it is still liquid. The clear sealant was one that released acetic acid during the cure. The black silicone was a normal cure with no acetic acid – I think this tube had been affected by the cold of last winter.

Please get in contact if you have any questions on this build.

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