Around a year ago, I went on a shopping spree for kits and ended up with a stash of them which I would attempt in my spare time. Chinese kits have all the fun of being relatively inexpensive, but also often lacking in clear instructions and sometimes components.
This time around, it is a “16-Tones Electronic Music Box” which I purchased for AU$2.57 including postage. I constructed it almost a year ago, but I never got around to documenting and posting about it. Given that I’m at home with the flu, it probably makes sense to just get this one off my chest.
In standard form, the kit comes as a zip-lock bag of parts and PCB. No instructions are provided.
The PCB is a quality double-sided silk-screened and soldermasked PCB with a HASL finish. Judging from the descriptions on the silkscreen layer, it should not be a big problem to build without any instructions.
The rest of the parts provided include even IC-sockets which is a good thing for beginner kit-builders. There is an odd component – a module including a gob-top chip-on-board. This is marked on the PCB as 9561 and is sometimes known as a CK9561. This appears to be a module used in children’s toys and is normally considered to generate four different tones depending on the connection of two of the pins. The Rf resistor at the top of the module sets the oscillation frequency.
Because of this, I already had my hunch as to what was going on – the additional circuitry would be switching in/out resistor values or modulating them to produce additional variations on those four base “tones”.
I decided to trace a schematic for this, but this was an exercise in frustration as this particular board is routed so efficiently that connections are made in a “spiderweb” fashion, hopping from the top to bottom layer at will at every via opportunity. Eventually, however, it seemed to take shape.
The two ICs used are a CD4011BE Quad NAND gate which is used to do some logic operations on the four bit input (set by switches with a 150k pull-down). This is fed to the module and onto the CD4066 CMOS Bilateral switch which is used to toggle in the resistance network on Rf. I didn’t feel the need to go much further, but do note the use of curved lines as a stylistic choice to better delineate crossing-lines. That was my second attempt to draw the schematic by hand, so I’m fairly happy with it, but as usual, there may be errors so use with caution.
Construction and Results
Construction of the kit is mostly straightforward, although the wider than expected slot made soldering the module more difficult than it would otherwise have been. As a result, I found it best to solder in the top two leads first, then solder in the module at an angle, and feed the two leads into the PCB base and solder them in as the final step. The wider-than-necessary slots continue for the switches, resulting in some slightly crooked switches, although it does not affect their function. Care should be taken to orient the IC sockets the right way (pin 1 notch).
In all, the solder resist and pad shape worked well for easy soldering – the thermal bridges preventing heat loss to the rest of the copper.
You can see the care I took to bend those scrap resistor leads for the Rf connection from the module to the PCB base board.
In the end, there were three excess header pins and one resistor. Better to have an excess than a deficit!
You can see from the image above, the music box sounds (audio recording) quite tinny and annoying. More like a noise-box that generates harsh harmonics, it sounds like a car alarm from the 90s and wouldn’t be described as “musical”. There may be 16 “sounds”, but a few of them are similar and all of them can vaguely be described as “alarm-like”. Did anyone say annoying?
It would be fair to say that this was probably not one of my favourite kits. While the PCB was a good quality, double-sided board with soldermask and screen printing, as well as solder-friendly pads, the compact design with traces jumping back and forth proved a headache to untangle. The smaller board with little room on all sides could prove a little more difficult for the novice, along with the slot for the module which is too wide. But as it is all through-hole style devices with the exception of the module, it’s still considered a fairly easy kit overall.
That being said, the description of the kit as a “music box” is a little irksome, as it isn’t really so much a music box as a noise box. For the most part, it sounds something akin to a tinnier version of those old 90s car alarms that played random harsh tones. Because of this, it doesn’t really have many applications except perhaps in a toy or in a pinch for a siren of sorts. I wouldn’t advise giving it to children, however, as if they manage to get it working, it could very much be used against you as a sonic weapon.
The only thing I can think of is that it could make some different noises if you change the various resistor values – even putting my finger over some of the connections effected a frequency shift, so it could be of interest to a circuit bender perhaps.