Lunchbeat is simple groovemachine with 8 step sequencer and four 1bit sounds.
START/STOP - runs or stops sequencer. When sequencer is started in external sync mode,
it waits for first TRIG in pulse. In SETUP mode this button selects internal or external clock. EDIT - cycles thru all sequencer steps from step 1 to step 8, I call this EDIT mode.
Selected step is marked with
fully light LED. SOUND BUTTONS - in EDIT mode you turn on/off sounds to be played on selected step.
When not in EDIT mode, sounds can pe played by pressing sound button at any time.
In SETUP sound buttons are used to enter TRIG division value. In binary! :) MOD POTS - each sound has dedicated potentiometer to tweak sound parameters in real time. TEMPO POT - tempo of internal clock generator.
(one of early Lunchbeat prototypes)
Lunchbeat can be switched to internal clock, so sequencer advances in intervals given
by internal clock generator, and so Lunchbeat sends short 5V pulses to TRIG connector,
serving as master.
Or Lunchbeat can be switched to external clock, TRIG connector is then turned to input
and sequencer advances when rising edge of 5V pulse is received.
Holding EDIT button for longer time gets Lunchbeat to setup mode
(tempo LED flashes rapidly). In setup mode you can select internal or external clock
and division factor of TRIG synchronization. With division factor set Lunchbeate is
receiving (or sending) every x-th TRIG pulse. Division factor "x" can be any number
from 1 to 15. Can be used for creating unequal floating beats. Leave setup mode by
holding EDIT button for longer time again. WARNING: there is no protection circuitry on TRIG IN input! So be sure your TRIG signal
does not exceed 5V! In other case you can fry your chip.
MCU RESET - mcu reset button is not usually implemented on music instrument. But my
assumption is that user will be messing with firmware, so there we go. I am using rigid
2.5N pushutton for this, to prevent reseting unit accidentaly. ISP6pin - hacker's gate to unit's microcontroller. Tweak the sound algorithms.
Tweak the sequencer.
Change unit's purpose completely.
Use the fact that Lunchbeat is the same thing as Arduino with 6 buttons, 5 pots, 8 LEDs on SPI shift
register and 3-bit digital to analog converter. You can run Arduino sketches on it.
From here it is up to you and your fantasy.
How it works:
Microcontroller Atmel Atmega328p is running at freq 16MHz. 6 buttons is connected to
digital input pins with enabled internal pullup resistors, and five potentiometers
connected to analog input pins. Audio is outputed thru
3-bit resistor-2-resistor digital/analog converter with LM358n operational amplifier in voltage
follower mode and DC blocking capacitor. 8 blue LEDs are controlled with 74595 shift register, to
which data is sended from MCU via SPI bus.
Internal sampling frequency is 15626Hz. So there is interrupt routine firing 15626x
per second. This routine checks if some sound should be playing, and if so, checks how long is that
sound playing already and than is computed value for output. Sounds are 1 bit, so output value can be
only 0 or 1, nothing else. After that all four sound values are summed together (mixed) and this final
mix value is pushed to 3-bit DAC.
How to get one:
A - You can buy one in sellout section on this web.
B - You can build one yourself.
Firmware source code, schematics, PCB design and partlist is in GitHub repository here:
Lunchbeat was designed for one of Lunchmeat-Neone workshops, to demonstrate how sound
can be made with 8-bit microcontroller. But the machine eventually proved
itself to be raised from breadboard domains to upper - more solid - printed circuit board states.
Original breadboard Lunchbeat is in this video:
Resources for original breadboard Lunchbeat
in GitHub repo: lunchbeat