A Lego toy that plays different tunes, that you
can play along to using the four gren keys. The notes each key plays
changes with the melody in a way that keeps them in harmony with
the tune. The sounds playing the melody and the harmony voice you
play on the keys are selected by placing different "plugs"
in two sockets, one for melody one for keys. The plugs have pictures
depicting their timbre, which can be different instruments as well
as soundeffects like carhorns and animals. It comes with four build
in tunes, but four more optional tunes can be selected if you use
a special cartridge that fits in a port at the back of the unit.
The white button cycles between the available tunes.
Voice Selectors. All sound data are in the unit; the
plugs merely selects a sound. A plug have three concentric contact
surfaces, that connects with contact pins in the socket when inserted.
Internally in the plugs the contact surfaces are connected with
two different resistors. Each sound plug have a unique combination
of resistors, letting the processor detect what corresponding sound
to use for the part of the socket.
With two testwires and an ohmmeter I decoded the different resistor
combinations for the sounds of all my plugs. After mapping the valid
resistor combinations two pairs of potentiometers could be scaled
and ofsett, using trimpots/fixed resistors in series and parallel,
to get the most optimal range that would let all valid combinations
be dialed in using the full scale of the pots. The pots are wired
to the circuit board at the points that connected to the contact
pins in the sockets. At some positions the values dialed are not
close enough to valid combinations and the program 'gets confused'
and jump somewhat randomly between sounds.
Melody on/off switch. Disables the
automatic melody. only what is played on the keys is heard.
Pitch/speed potentiometer. This potentiometer
change pitch and speed by changing the clock speed of the processor.
Placed in the socket for the keys plug.
[extra nerd info: the potentiometer is a dual potentiometer where
the second pot, suitably scaled and offset, serves as a variable
minimum resistor in series with the pitchbend depth potentiometer,
as the minimum resistance needed to protect the circuit from craching
varies with the clockspeed. Using a variable minimum resistance
insted of just a fixed resistor gives a better operation range of
the depth pot at both low and high pitch/speed settings]
Pitchbend and Pitchbend Depth.
The blue momentary pushbutton lowers the pitch (and playback speed)
when activated. The depth of the pitchbend is controlled with the
LDR with on/off switch A LDR (Photo
Cell) is placed in the socket that used to hold the melody plug.
When enabled pitch/speed is affected by the amount of light on the
LDR. Playable by manually shading the LDR from ambient light or
using the LED Blinker Plug or any other handheld lightsource.
LED Blinker w. intensity pot.
A LED connected to a LFO circuit built into the main unit, is placed
inside one of the sound plugs. The plug can be placed in the socket
for a constant modulation or can be moved with the hand to fade
modulation in and out. The intensity potmeter can dim the LED and
thereby control modulation depth.
LFO with Rate pot and
Waveform switch. The LFO produces two simultaneous waveforms:
square wave and an asymetric waveform somewhere between a triangle
and a falling sawtooth wave. The switch routes either waveform to
the LED. In the middle position LFO output is off (LED not blinking).
Output. A 1/4'' jack
socket with a Speaker/Output off/Line out switch.