Project: HX-1021 “Green Lighting” LED Color Small Night Light Kit

Gough’s kit crusade continues with this HX-1021 “Green Lighting” LED Color Small Night Light kit, costing just AU$2.73 including postage. This one was incorrectly listed on eBay as a “mains motion light”, but the lack of a PIR detector is a dead giveaway that it was just going to be responding to brightness with an LDR. Anyway … time to get building?

The Kit

The kit arrives in a box which seems to claim there is a night light already inside. No mention that it is a kit on the exterior, so I wonder whether this is a real product that they just decided not to assemble themselves and turn into a kit? Nonetheless, this feels a bit like IKEA – some assembly required.

The English on the packaging is quite laughable – excellent quality? I doubt it. The light is downy? Okay … whatever that means. I suspect they mean “soft”. Save electricity practical? I’ll be the judge of that.

The other panel was also rather amusing – “This Product’bright lamp-hoursurface show red orchid green three kind or color,color beautiful.” Riiiiight … moving on.

Inside, there is a piece of paper, the casing for the product and a slightly stained plastic bag with components.

The casing is made of a somewhat “dirty” white plastic that has some rather noticeable moulding defects. That being said, it does seem to fit together acceptably, even if the plastic seems a bit chalky and brittle. The lens for the LEDs is a patterned diffuser which looks rather prismatic.

Already, from the bag of components, we can tell that the “colour” of the night-light is just the colour of a tiny bit of plastic trim. Nothing to be too excited about. The components already betray the fact this will be a capacitive dropper design, with the notable inclusion of a polyester “dipped” capacitor that seems to be under-rated (250V DC) and not quite of the best type. The mains prongs are included as a separate component and the straw-hat white LED legs are somewhat tarnished. A piece of insulation tubing is included too.

The PCB is a relatively low-quality board of the paper-type. It has silkscreening on the top side with rather rough edges.

The underside is lacquered copper with a soldermask layer and nothing special in terms of pad shaping to aid solderability. A very average effort on this part, but given the simplicity of the circuit, shouldn’t be too difficult to construct regardless.

Unlike most of the other Chinese kits, this one does come with a half-page information leaflet containing an explanation in Chinese, the bill of materials, schematic and PCB layout. From what I can see, this is a “classic” capacitive dropper design of the sort that bigclivedotcom sees on the regular, with a zener-shunt regulation meaning that the circuit probably consumes the same amount of power whether the LEDs are on or off. It does have a flicker-reduction capacitor across the LEDs, but other than that, it’s very much a minimalist design which should mean there is not much to get wrong either.

Construction

Before beginning construction, lets do a quick computation of the number of solder joints necessary to complete the kit:

4 x LEDs - 8
Transistor - 3
5 x Diodes - 10
2 x Capacitors - 4
4 x Resistors - 8
LDR - 2
Mains Wires - 2
Mains Pins - 2
Total: 39

The number of connections is rather limited so it should be a walk-in-the-park, proverbially speaking, even with the “low cost” paper-substrate copper-lacquer type PCB. It’s a case of populate and solder-down, although you will need to leave most of the legs on the LDR so it can protrude into the casing hole and sleeve one of its legs to prevent the LDR from shorting out when manipulated into its final place. Also good to leave some length of wire from the mains, although you could trim it back about halfway to make it a little neater.

At this point, I forgot to take an image of the rear of the PCB, but you can already imagine, it’s nothing special … just a number of solder joints.

The supplied prongs need to be pushed through the slots in the casing. It is a very tight fit, so a hammer and some patience are required.

Then, it is a case of soldering to these pins which is a little awkward given the shape of the casing. Due to the high thermal mass of the pins, a hefty iron is recommended, but avoid overheating the pins if you can.

The board them nestles into the bottom, secured to the rear casing by a single screw. The whole casing then can be snapped together, with the LDR positioned through the hole and the window fitted.

The “colour” front trim panel can also be affixed. In fact, I strongly recommend that you fully assemble the case before testing as the circuit is not isolated from the mains, thus the casing serves as vital insulation for the user and protects the user in case you get any “magic smoke release” events.

As I applied a little bit too much heat to one of the prongs while soldering the wire connection to the rear, the channel within the plastic body must have melted slightly allowing the pin to skew slightly. No major issue as it will still fit into my adapter plug and is still snug in the body so as not to fall apart.

Testing

Plugging a mains kit into the wall for the first time is a little bit of a frightening moment. On the one hand, you hope you’ve done everything right and it will work. On another, you know if you did do something wrong, you’re probably going to find out about it rather quickly as mains is somewhat unforgiving. With a kit such as this one with no spare parts … it could be game over unless you can find suitable replacements from your “junk box”.

I plugged my unit in and … absolutely nothing happened. Knowing that it is a “night light”, I covered the LDR with my hand rather gingerly (as I didn’t fancy an electric shock either due to the non-isolated nature of the circuit). Nada.

I scratched my head and thought “maybe I placed the LEDs the wrong way around again …” but that wasn’t the case. I powered the string of LEDs from a bench supply (~12V DC to reach 20mA) and they worked just fine. I didn’t see any bad joints either.

It was at this point, I plugged it into the power analyser and I saw that there was some current draw. I finally turned off the lights in the room, hypothesizing that the light must have gotten in through the slightly “thin” casing and the LDR was very sensitive. To my surprise, it works just fine and I didn’t make any mistakes … phew!

Looking at the power consumption seems to show the unit consuming about 0.699W or thereabouts whether the LEDs are on or not, which is a bit of a shame but not a big surprise.

Conclusion

This low priced LED night-light kit is a bit of a surprise. For the price, we do get a nice enclosure and a working night-light, although the design is a crude capacitive dropper, it does have some smoothing on the output. The included leaflet is a good help with the schematic on it, although the quality of the components (especially the rating of the capacitor, the paper-type PCB and the moulding of the plastic case) is a little lacking. As with mains kits, the non-isolated nature of the circuit needs to be kept in mind when testing – touching any part of the circuit when powered is a bad idea. Also, as always with mains kits, extra care needs to be taken during construction to ensure no “magic smoke” events occur.

The biggest downside aside from the under-rated capacitor seems to be the fact the light draws about 0.7W whether the LEDs are on or not, so aside from a loss of LED lifetime, there doesn’t seem to be a big point to turning the LEDs off when it is bright as there is no energy being saved.

About lui_gough

I'm a bit of a nut for electronics, computing, photography, radio, satellite and other technical hobbies. Click for more about me!
This entry was posted in Electronics and tagged , , , , , . Bookmark the permalink.

Error: Comment is Missing!