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.

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Project: EQKit PSK-1 Electronic “Voice Control” Switch Kit

Continuing the kit-a-thon, I grabbed another EQKit out of the drawer – this one is a PSK-1 which was sold as an Electronic “Voice Control” Switch Kit for the princely sum of AU$1.98 including postage. As a kit that had nothing too complicated in it, how could it possibly do voice control?

The Kit

A zip-lock bag – but instead of containing contraband items, it contains components for the kit.

As seems to be classic with EQKits, they come with the extra frills – a JST cable and socket for power, aside from the necessary components. That’s a nice touch.

The PCB also is of a good quality, being single-sided this time, silkscreening on the top.

The underside having solder-resist and hot-air levelled tin finish for easier soldering. The pads do get somewhat close together, so a fine iron is probably best.

Construction

A quick count of the solder joints needed to build the kit:

14 x Resistors - 28
4 x Transistors - 12
6 x Capacitors - 12
2 x Diodes - 4
Microphone - 2
LED - 2
Power Socket - 2
Total: 62

Another straightforward construction – interestingly, nothing is provided to populate J1 and its purpose is not immediately apparent due to the lack of instructions or information.

Fairly neat solder joints – I did this after work in my time just before bed, so I was in a rush – but the boards from EQKit are always a joy to solder to.

Testing

Ever curious as to what it does, I hooked it up to power and tried speaking to it. Nothing. I tried tapping on the mic … but nothing happened. I even tried clapping … then I realized I mounted the LED backwards. D’oh! Just goes to show that experienced kids like myself make mistakes when they’re tired – so don’t build kits when you’re tired (or drunk)!

Take #2 was much more successful – now the LED was positioned correctly, I found that clapping or clicking would toggle the LED on or off. Quickly double-clapping would not trigger it twice, so it has some sort of “debounce” time. That actually reminds me of The Clapper switches which used to be rather popular. It doesn’t even need any adjustments.

Wanting some insight into how it worked, I tried to trace out the schematic which took multiple attempts due to the numerous cross-connections. I’m not even sure if the above is correct, but not having the time to analyse it in-depth, I’m none the wiser as to how it works.

Observing the bases of the transistors through the oscilloscope seemed to give me some hints – Q1 seems to be just biased with an “impuse” causing it to shut hard off. This seems to propagate to Q2 which shows a much harder “square” drive, all with about a 300ms time constant. Then Q3 seems to be triggered toggled between claps, whereas Q4 seems a bit of a mystery although it should be driving the output in some way … I’m not sure what happened there. But it does work and it seems to be a rather interesting module to integrate into another project (potentially).

Conclusion

As with most EQKit products, this one was rather straightforward to build despite the lack of instructions, and the board was fairly enjoyable to solder to. This one was rather interesting, as it was sold as a “voice control” kit but rather is more akin to a “clapper control” – clap to turn on/off.

The way it works is a slight mystery to me as well, as it has a rather interesting cross-connection of components, but from the oscilloscope trace, it seems to involve “just” biased transistors, some filtering, a time-constant of about 300ms somewhere and some diode logic of sorts.

Regardless, it does perform a rather neat function and it seems to work quite well. Speech doesn’t trigger it – but claps and clicks do. It seems useful as a module in other projects, hence the J1 output which could be input to a microcontroller (e.g. edge-triggered interrupt).

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Project: EQKit MDS-60 Electronic Metal Detector Kit

As a fan of building kits, my crusade to try building random cheap-Chinese kits continues with this EQKit MDS-60 Electronic Metal Detector Kit which I managed to get for AU$1.84. Being such a low-cost item, we don’t expect to build a practical metal detector (the kind you’d walk to a beach with to scan for loose change), but we might have something that does do … something?

The Kit

Another plastic zip-lock bag … we know the drill by now!

Not unexpectedly, for a low-cost kit, the number of components are only just a handful – resistors, transistors, capacitors, an LED, buzzer, potentiometer, switch and terminal block. Still nice to see they didn’t skimp on the switch or terminal block … EQKit seems to make rather decent stuff.

The PCB is a double-sided fibreglass board with white skilscreen on the top and soldermask on both sides.

The PCB is a work of art with its printed trace inductor coil – a close look at the silkscreen sees little soldermask cut-outs which say EQKIT around the circumference of the windings. That’s attention to detail and a quality PCB manufacture to get these to register exactly.

Unfortunately, no instructions nor schematics were supplied.

Construction

A quick computation on the amount of joints needed to complete the kit:

5 x Capacitors - 10
3 x Transistors - 9
3 x Resistors - 6
Potentiometer - 3
Switch - 6
Terminal Block - 2
Buzzer - 2
LED - 2
Total: 40

Construction was straightforward – populate and solder …

… a relatively trouble-free build with some fairly tight transistor pad spacing (a thin iron is best) but due to careful board design with thermal-isolation on pads near ground planes, it was a breeze to construct.

Testing

Testing it was as simple as applying 5V to the unit and adjusting the sensitivity until it beeped, and backing off slightly. Introducing some metal resulted in the detector “going off”, as it should. Magic!

But then I thought … well, how does it work exactly? So I traced out a schematic. Because of the point-to-point type double-side layout, it took me a while to get something which seemed sensible, but errors may still exist.

I suspect this design is a self-oscillating design with a drive and sense coil, and successive stages of filtering and amplification to drive the speakers and LED through Q3. How it exactly works is still a mystery to me – is it increased coupling between the two coils causing the detection or is it the phase-relationship being thrown off in some way. I didn’t spend much more time analysing this – I had too much else on my plate …

Looking at the drive of the coil on the oscilloscope seems to suggest it oscillates at about 275kHz. NDB band users probably won’t enjoy the radiation that might be emitted from this – it’s probably functioning as a low-power CW transmitter!

Introducing some metal into the equation changes its frequency due to a change in inductance but there are now some spikes measured on the base of a transistor in the design (I don’t remember which) – this is probably the small signal that is being amplified signifying detection? I’m not entirely sure … maybe I should have a proper sit-and-think about this one.

Conclusion

For such a low-cost kit, this one was a bit of a surprise. It definitely does detect metal at a fairly short (10cm) range depending on your sensitivity setting. But the quality of the PCB was excellent, with some delicate details and layout.

Unfortunately, it didn’t come with explanations or schematics, so I did some tracing but yet, without enough time to fully study it, I’m not much wiser as to how it works. I suspect the central coil is a drive coil with the outer loop as a sense coil, so perhaps the coupling is what is used to detect metal (due to permeability increasing coupling much like how a core in a transformer increases coupling). But probing with the oscilloscope seems to suggest another possibility – perhaps the circuit is designed as a “tuned” circuit and the change in inductance with the introduction of metal throws off the phase relationship of the feedback resulting in a voltage developing that is successively amplified as the output.

Either way, it was a fun kit to play with, along with its annoying buzzer. The PCB coil is in my opinion, a work of art.

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