Xin Anda - 8-Melody Letter Study Piano (weird toy tablehooter with animal sound & alphabet letter samples)

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.

main features:





The squarewave musicbox timbre (called "piano" in manual) ignores key press duration. Due to a strange multiplexed keyboard matrix scheme, sometimes weak key or button presses trigger wrong functions. While the octave wrongly begins on the 'B' key (an ratio to the sharps), the number strip above the keys correctly starts there with '1'. (With Jin Xin JX-20165 it is vice versa.)
The buttons have no names thus here is what they do. The circle of triangular buttons select the main modes. Counting clockwise from the upper left button they are {piano, piano demos, animal sounds, animal demos, modes}. Each button plays a polyphonic jingle before it takes effect. In "animal sounds" mode you can select the 5 preset sounds with the oval OBS preset sound buttons, those each play their sound when pressed. In "piano" (squarewave musicbox) mode these buttons only play their sound but don't change the main voice. In "piano demos" mode each key selects a demo song in 2 note polyphonic squarewave musicbox sound. In "animal demos" mode these demos additionally have a sample voice that cycles through the 5 animal preset sounds (sound is selected by the note pitch of one of the squarewave channels?). The "mode" button simply cycles through the functions of the 4 other triangular buttons and a 5th function that plays the demos in monophonic musicbox sound and then switches into "one key play" mode. The blue button left next to the keys starts the alphabet learning mode.

circuit bending details

The 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 matrix

This 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.)

volume control

To add a volume control pot, cut the (center) base pin of the transistor on the top side of the PCB. Connect a potentiometer (mine is 5 kOhm) with its right end to the now open CPU sound output (where the base pin was connected). Connect the wiper with the transistor's base and the left end with GND.

The 8 monophonic demo melodies are selected in "piano demos" or "animal demos" mode through white keyboard keys and/ or the rectangular "sharp" buttons.

  1. Old McDonald Had a Farm
  2. Mary Had a Little Lamb
  3. Oh Susanna!
  4. Jingle Bells
  5. Twinkle Twinkle Little Star
  6. This Old Man
  7. Row, Row, Row the Boat
  8. London Bridge Is Falling Down
Toy keyboards with very similar case shape but 37 midsize keys and no alphabet buttons were released by Yongmei as YM-9903A (red, with key lighting?) and YM-9902B (light blue); both seem to contain My Song Maker hardware variants.
 removal of these screws voids warranty...    
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