Circular LED Chaser kit bash

I bought myself a bunch of kits from China to use as soldering practise and to try to find out how they work. The first one I attempted was this “Colorful Voice Control Rotating LED Light Kit …”:

After soldering everything together I discovered that nothing worked. It seemed I'd bridged two adjcent PCB holes with solder. On trying to remove the bridge I managed to cut through some tracks that were routed close to the holes.

Instead of throwing the board away - I mean it cost me all of £1.22 - I decided to see if I could salvage something from the mess.

After a lot of head scratching and poking around with wires and the multimeter I decided I wasn't going to be able to save the board as designed, but that I might be able to patch it up so that at least the CD4017 decade timer could cycle through the LEDs.

So, I de-soldered all the components that were part of the sound section of the circuit and went about soldering wires to the back of the board until all the problematic tracks had been bypassed. As you can see in the following photo, there were a lot!

While doing the patching I soldered on a wire from the CLK pin of the CD4017 that could be used to trigger the counter and so test that the counter would light all LEDs in sequence. They did … progress!

Now that the CD4017 and the LEDs were working I hit upon the idea of using the kit as the basis for a circular LED chaser. For that I decided to use a 555 timer to trigger the CD4017. I breadboarded a circuit and messed arond with various resistor and capacitor values until I got the chaser running at a speed I liked. A trim pot was included to enable the trigger speed to be adjusted.

Here's the circuit I settled on:

Everything on the right of the above circuit (including the 4017 chip) was pre-determined by the remaining content of the circular PCB that came with the kit. Everything to the left of the 4017 was new.

OK, I'd got a working circuit. But what to do with it? I'd recently bought a 6cm diameter perspex globe from the Pi Hut so I decided to mount the chaser in that. This meant that the 555 timer circuit would have to piggy back over the CD4017 chip on a daughterboard. Out came the soldering iron again and I put together the required board, which was sized to fit in the globe.

Testing with the LED chaser circuit board showed that everything worked, as the following video shows:

Having proved the circuit worked I glued the daughterboard on the back of the circular board using some scrap plastic offcuts and UHU glue. Black electrical tape was used for insulation. The corners of the daughterboard were trimmed off to ensure they couldn't be seen from the front.

The next job was to make a gasket to hold the board inside the globe. I made two rings of the required internal and external diameters from cereal box card. These were laminated together with Roket card glue, painted with black acrylic paint and then glued to the round circuit board with super glue.

The ring was such a good fit inside the globe there was no need for glue to hold it in place:

As can be seen in the back view of the globe above, a hole was drilled to provide access to the trim pot. Unfortuately I caught the trim pot with the drill and broke of the plastic fitting for the screwdriver. I couldn't mend that but luckily, the screwdriver can still be used to turn the trimpot.

I first considered using batteries to power the circuit but decided instead to power it via a USB micro socket. This decision was made because I wanted to mount the globe on a stick, like a wand, and a USB socket could be mounted at the end of the wand. Therefore two power leads were routed out of the globe through a hole drilled behind the loop from which the globe was intended to be hung.

An offcut of tubular metal curtain pole was used as a wand. Attempts to glue the globe to the wand failed, resulting only in a small amount of damage to the bottom of the globe! In the end I went for a push fit which entailed adding layers of shrink wrap to the wires and adding some double sided foam tape to the inside of the tube.

All that was needed now was a base for the whole thing to stand on. The initial idea to use the glass jar lid seen in the above video was quickly discarded. Then I came across the base of an old wireless phone and decided to use that. The base was drilled to accept the wand and a slot was made in the rear of the base to accommodate a USB B micro socket. The USB socket was purchased ready soldered to a small PCB. This is turn was attached to an offcut of perfboard and the wires from the globe were soldered to it:

The tube was push fitted into the hole in the base, padded with double sided sticky foam tape. The tube was tilted back to be supported by the back of the phone cradle.

The following photos and video show the finished product. It's a bit rough and ready, but it'll really only be used in a dark setting over Christmas, so I'm not too concerned. It's also gratifying to finally finish this thing!

I eventually bought another copy of this kit and managed to build it correctly.