The creator of this Chinese toy tablehooter must have been dement or drunk, because the keyboard octave starts with 'B' instead of 'C', and despite the CPU supports 10 sharps, all black keys are fake and play the same note like the white key left next to it, and 8 of the sharp notes are even located on rectangular buttons instead. The control panel also has no writing at all - possibly the case and PCB designer did not even know the exact functions of the CPU.
The thing from 2002 (PCB date label) has no volume control and yells ear- tormenting loud with some grungy analogue transistor distortion. The monophonic main voice can be switched between a plain squarewave music box timbre and 5 low resolution animal voice samples. Most unusual are the 26 alphabet letter buttons, those each say their letter name in English and there is even a primitive audiogame that says a letter name and the player has to press the corresponding letter button; correct presses play an applause, wrong ones a spring noise. During the game there is a monophonic squarewave monoto (melody loop) and every few correct letters it plays the same polyphonic squarewave jingle, which nicely reminds to historical videogames. But the low resolution sample voice mumbles so dull that it is barely to understand, and the 'Z' is even pronounced "zee" instead of "zet", which makes of it the perfect toy to annoy parents and confuse toddlers until they have completely unlearned all correct piano playing skills and letter names. There are also some nice polyphonic squarewave demos with optional animal voices.
The OBS alphabet letter buttons may be interesting for tekkno to spell words and form English sentences ("I-M-A-DJ", "Y-R-U-A-DJ" etc.) and they also permit to rapidly retrigger their sample. I also like the mode intro jingles with polyphonic squarewave and grainy sample sound, those have this wonderful grungy old videogame style.
circuit bending detailsThe CPU employs a resistor controlled clock oscillator that can be used to add a pitch control. The power amplifier is made from 2 transistors (the 2nd is below the PCB). The count of the 26 letter + 5 animal samples + 1 squarewave sound sum to exactly 32, which is a power of 2 and might be a technical addressing limit within the quirky CPU. (But additionally there are also "applause", "sproing" and a tooting bass sample, thus in total there are 35 sounds.)
keyboard matrixThis instrument has the messiest keyboard matrix I ever saw. At the CPU it has 8 inputs and 4 individual output lines, but 3 additional output rows connect simultaneously to one output through a diode and another through a resistor (connecting both output directly for a test selects the same functions). Another output row connects simply to +Vs. While this still makes sense to save IC pins, it makes no sense at all anymore that the order of the notes and alphabet letters ascends and descends alternatingly in different rows, and the places for the 10 sharp (black) keys use different rows than the flats and the sharps are in almost random order. (With normal keyboards all notes of black and white keys are in a monotonous order from the lowest to the highest note.)
adding sharp keys:
The CPU has the 4 keyboard matrix outputs O1..O4 at pin 1..4 and the inputs I1..I8 at pin 5..12. The 8 sharps are on the 8 rectangular buttons those output line is connected with a diode coming from O4 and a resistor to O1. 2 additional sharps can be connected at I1 and I2 against +Vs (pin 14) through a low resistor. Theoretically the keyboard PCB could be likely upgraded with sharps, but it would be a lot of work to cut and almost all traces to the keys and re-wire them with coil wire. Also the keyboard could be certainly aligned correctly by transplanting the keys 25 and 26 to the left end of the keyboard.
one key play:
A one key play button can be connected at I4 through a low resistor against +Vs. (This feature can be also accessed through the "mode" button at the left side of the circle.)
The 8 monophonic demo melodies are selected in "piano demos" or "animal demos" mode through white keyboard keys and/ or the rectangular "sharp" buttons.
|removal of these screws voids warranty...|