I couldn’t help myself, so once I finish one kit, it’s often straight onto another. This kit was sold as an electronic LED hourglass and was a little more expensive at AU$3.07 including postage. Compared to local suppliers, this is a bargain – one major supplier in Australia wants AU$8.95 for a two transistor flasher kit, so I thought I’d build one of these instead and try it out.
Another clear plastic zip-lock bag. Maybe I should call these “fun bags” from now on … or maybe not. *looks awkwardly around in case anyone heard me say that*
Inside, there is a double-sided quarter page leaflet in Chinese with (presumably) instructions, PCB layout, bill of materials (BoM) and schematic. Already, we can see that the circuit uses a microcontroller, an obscure STC 15W201S, with the ability to be reprogrammed through a serial ISP header. This unfortunately means that the kit is probably not as educational as something with more traditional chips – the source code for the current program isn’t provided either. The circuit runs LEDs using a complimentary visual multiplexing matrix drive, so while not as complex as Charlieplexing, does at least allow for twice as many LEDs to be controlled as compared to regular visual multiplexing and makes debugging somewhat easier. Curiously, the BoM lists a capacitor that has no position and omits a USB connector.
The supplied components are, as listed in the BoM, so I suppose that’s what they intended to supply. It is a good idea, wherever you use microcontrollers, to have a bypassing capacitor installed near the chip itself but the leaflet makes no mention of a provision for it. The inclusion of an IC socket is a good feature, although I’d have to criticize them for including such a rusted, crusty push-button switch. There is also a quality control slip as well.
The PCB is a double-sided fibreglass type PCB with green soldermask on both sides and white silkscreen on the top. The pads are tin plated-through-hole, which makes this a pretty decent quality board for a kit. The board has the identifier TJ-56-205 on it, which suggests it is related to the heart flasher kit built in the last post.
Rather sadly, in the packing process, it seems that the board did suffer some abrasion but was not functionally damaged.
Construction and Testing
This kit is one that seems to require a substantial amount of work to complete –
57 LEDs x 2 connections 1 IC x 16 connections 1 switch x 5 connections 1 power jack x 3 connections 1 ISP header x 4 connections 1 switch x 4 connections TOTAL - 146 joints
Construction was, however, very straightforward because the orientation of LEDs was consistent, the board was well labelled and the pads (while small) were tinned. The only thing it took was time – about 55 minutes for me to complete including distractions and photographing.
In the end, three spare LEDs were included, which is a nice touch. However, the negatives were the rusty push-button switch which was found to be somewhat intermittent in functioning, the lack of USB connector (for a more popular way to power the circuit), the lack of a capacitor position on the board, the “blind” use of a rather obscure microcontroller to perform all the functions and the almost unnecessarily thin traces (which might make damage more likely).
The unit, when operating, runs like this, displaying a rather long animation that simulates grains of sand falling from the upper to the lower portion. This “abruptly” resets to a full top-half once the bottom-half is full. The push button allows you to toggle between three speeds.It’s not particularly inspiring, but the LEDs are quite bright and the visual effect is somewhat eye-catching. It’s a shame that the microcontroller is a little obscure, otherwise the LEDs could be used to display something else entirely (or maybe a more flexible hourglass that actually functions as a timer).
While this kit was slightly more expensive than some others, it’s still very cheap by local standards. The cost is understandable, especially when you consider how many high-intensity LEDs were included and the quality of the double-sided fibreglass PCB. Construction was very straightforward, with only minor negatives in the fact that everything is hidden inside an obscure microcontroller with no source code, that the traces seem unnecessarily thin on the board, that a USB connector for easier powering was not included, that the push-button switch included was rusty and intermittent and that no position is provided on the board for the capacitor which I would deem good practice.
That being said, the tin plated board was a joy to solder to and the consistent LED direction made things a lot quicker than it would have otherwise been. The effect is also quite bright and visually distinctive. Having three spare LEDs and an IC socket makes this kit quite recommendable for someone who wants a decent amount of through-hole soldering practice, with a good chance of success.