Microchip has recently released a new PIC micro, the PIC12F683,
with twice as much memory as the original PIC12F629 used within the
PICAXE-08. This has allowed Revolution Education to develop the
PICAXE-08M, an enhanced PICAXE-08 with in-built music playing
capabilities – and much more.
Fig.1: the pinout diagram for the new
The PICAXE-08M supports all of the standard commands and features
of the PICAXE-08, with the following enhancements:
- Program memory has been doubled in capacity (approx. 80 lines
- Musical tune playing capability, user generated or four
pre-programmed tunes (play and tune commands).
- 10-bit ADC option on 3 pins (read-adc10/readadc
- Interrupt feature on inputs (setint command).
- Infrared remote control input and output
- Continuously driven PWM motor drive output (pwmout
- Control of radio control type servos (servo command).
- Count high frequency pulses within a set time period
- Accurate digital temperature sensor interface
- Read serial number from any Dallas 1-wire device (eg, iButton)
- Software support for increased (8MHz) clock frequency
Note that all existing PICAXE-08 programs will run on the 08M
Fig.2: with the aid of a PICAXE-08M micro and
simple software, the circuit can flash Rudolph's nose and eyes and
play a seasonal tune. The infrared receiver (described next month)
allows remote selection of one of four possible tunes.
Playing tunes on a PICAXE
The main obstacle when playing tunes on PIC microcontrollers is
limited memory space. All the PICAXE chips have a sound
command to make noises. However, the number of notes and playback
speed, or "tempo", is very limited, as the sound command data
rapidly consumes all available program memory.
To overcome these issues, the PICAXE-08M has a newly developed
tune command to play music. The tune command
incorporates a note data compression algorithm to save memory space.
It is also pre-programmed with four melodies: Happy Birthday, Jingle
Bells, Silent Night and Rudolph the Red Nosed Reindeer. In addition,
it can be programmed with the mobile phone ring tone of your
Mobile phone ring tones are widely available on the Internet in
"ring tone text transfer" format (RTTTF), as used on most Nokia
phones. Although some web sites charge for ring tone downloads,
there are still a number of sites that provide these free of charge.
A simple microcontroller cannot play complicated "polyphonic" tunes,
but can make a good attempt at playing "monophonic" (one note at a
Fig.3: follow this diagram closely when
assembling Rudolph. Note in particular the orientation of the three
LEDs and the PICAXE micro as well as the power supply positive and
Fig.2 shows the circuit of our simple Christmas decoration, with
the PCB shaped in the form of Rudolph’s head. Output 0 is connected
to a 10mm red LED, forming Rudolph’s nose. Output 4 drives two
smaller green LEDs for the eyes, whereas a piezo transducer on
output 2 plays the tune. Inputs 1 and 3 are connected to a
light-dependant resistor (LDR) and push-button switch.
In this circuit, the PICAXE-08M micro can be programmed to play a
tune when the switch is pressed and/or the light level (sensed by
the LDR) changes. Note that the push-button switch circuit is
"active low" for compatibility with the infrared upgrade, which will
be described next month.
The supplied piezo transducer does a reasonable job of tone
reproduction. For a richer sound, it can be replaced with a low-cost
40Ω speaker if desired. Wire one of the speaker leads in series with
a 10μF electrolytic capacitor before hook-up to the PC board.
A kit of parts that includes the pre-shaped PC board will be
available from your usual PICAXE reseller. The PC board overlay is
shown in Fig.3. Assembly of the board is very straightforward, with
attention to the points listed below.
Although the infrared sensor (IR) and capacitor (C1) appear on
the circuit and overlay diagrams, they are required only for remote
control operation and can be left out for the moment.
Fig.4: this piano keyboard representation shows
the key frequencies in octaves 5, 6 and 7. This is the range of
frequencies covered by the PICAXE-08M.
Take care with the orientation of the three LEDs, which must have
their flat (cathode) sides positioned as shown. Also, make sure that
the notched (pin 1) end of the PICAXE micro faces the serial link
socket. Before soldering the battery clip leads, thread them through
the adjacent hole to provide strain relief.
Power your completed project only from a 3 x alkaline AA cell
(4.5V) battery pack or regulated 5V DC supply. Take particular care
that you have the power leads around the right way, otherwise you’ll
destroy the PICAXE!
The following paragraphs explain how the music encoding process
works. If you’re not interested in the technicalities and just want
to play tunes, you can skip directly to the "Tune Wizard" section
|Bit No. 7, 6 - Duration
||Bit No. 5, 4 - Octave
||Bit No. 3, 2, 1, 0 - Note|
|00 = 1/4
||00 = Middle Octave (6)
||0000 = C|
|01 = 1/8
||01 = High Octave (7)
||0001 = C#|
|10 = 1
||10 = Low Octave (5)
||0010 = D|
|11 = 1/2
||11 = not used
||0011 = D#|
||0100 = E|
||0101 = F|
||0110 = F#|
||0111 = G|
||1000 = G#|
||1001 = A|
||1010 = A#|
||1011 = B|
||11xx = P (pause)|
Notes: 1/16, 1/32 and 'dotted' notes are not supported.
Only octaves 5-7 are supported.
Fig.5: the encoding of each note byte used by the tune
The tune command has the following syntax: tune
led, speed, (note, note, note . . .) where:
(1).led is a variable/constant (0-3) which specifies if
other outputs flash at the same time as the tune is being played;
0 = No outputs
1 = Output 0 flashes on and off
2 = Output 4 flashes on and off
3 = Output 0 and 4 flash alternately
(2).speed is a variable/constant (1-15) which specifies
the tempo of the tune.
(3).note, note, etc is the encoded musical note data.
Most ring tones use notes from octaves 5, 6 and 7 (octave 6
starts with "middle C" for the piano players!). A graphical
representation of these notes compared to a piano keyboard is shown
Fig.6: import RTTTL tunes or create your own
with the Tune Wizard, included in versions 4.0.1 and later of the
PICAXE Programming Editor
There are 12 notes to an octave (including incidental notes), and
if you add pause, this gives 13 different possibilities. As the tune
plays, each note also varies in duration, and most ring tones use 4
different lengths - notes of duration 1/8 (quaver) 1/4 (crotchet)
1/2 (minim) or 1/1 (semibreve). Theoretically, notes of 1/16 and
1/32 are also possible, but only a few ring tones use these
durations and so they are not considered in our algorithm.
Considering this information, each note byte can be encoded into
just 1 byte of memory as shown in Fig.5. The encoding is optimised
to ensure that the most common values (1/4 beat and octave 6) both
have a value of 00. Note that as the PICAXE also performs further
optimisation on the whole tune, the length of the tune data will not
be exactly the same length as the number of notes in the tune.
Fig.7: this table shows the equivalent tempo in beats/ minute for
the 15 possible speed values.
The speed of music is normally called "tempo", defined as the
number of quarter beats per minute (BPM). The PICAXE tune command
allows 15 different speeds (1-15) calculated as follows:
The sound duration of a quarter beat within the PICAXE is given
by the following formula:
sound duration = speed x 65.64ms
Each quarter beat is also followed by a silence duration, given
silence duration = speed x 8.20ms
Therefore, the total duration of a quarter beat is:
total duration = (speed x 65.64) + (speed x 8.20) ms = speed x
The approximate number of beats per minute at different speed
values is shown in Fig.7. The chosen values give a good range for
most popular tunes.
Note that within electronically generated music a note normally
plays for 7/8 of the total note time, with silence for 1/8. With the
PICAXE-08M the ratio is slightly different (8/9) due to the memory
and mathematical limitations of the microcontroller. However, unless
you are a gifted musician you probably won’t notice the
The Tune Wizard within the PICAXE Programming Editor software
(v4.1.0 or later) allows musical tunes to be created for the
PICAXE-08M. Tunes can be entered manually using the drop-down boxes
if desired but most users will prefer to import a mobile phone
monophonic ring tone.
Note that the PICAXE can only play one note at a time
(monophonic), and so cannot use multiple note (polyphonic) ring
A typical RTTTL ring tone, as downloaded from the Internet, is
shown in Fig.8. The first few text characters describe the ring tone
name, then the default characteristics (default note duration = 1/4,
default octave = 5, bpm = 125), then each note in turn. This ring
tone can be imported straight into the Tune Wizard. The Tune Wizard
will then automatically generate the BASIC code required for the
The tune can also be tested on the computer by clicking the
"Play" menu (assuming the PC is fitted with a soundcard and
speakers). The tune played will give you a rough idea of how the
tune will sound on the PICAXE, but will differ slightly due to the
different ways that the computer and PICAXE generate and playback
The "outputs" section of the Wizard interface allows you to
choose which outputs flash on and off as the tune is played. For the
Rudolph project, select both outputs (nose and eyes!)
Fig.8: Star Wars Theme Tune In RTTTL Format
The program listing shown in Fig.9 demonstrates how to play a
tune when the switch is pushed.
The tune played will vary between four different melodies,
depending on the light level falling on the LDR when the switch is
pushed. Three of these melodies (Jingle Bells, Silent Night &
Rudolph) are pre-programmed tunes included within the PICAXE-08M
bootstrap program and are activated by the play command.
The final melody ("We Wish You a Merry Christmas") is a
user-defined tune, generated by the Tune Wizard, and played with the
The play and tune commands allow you to play simple
musical tunes on the new PICAXE-08M. There are approximately 1000
tunes for free download on the software page of the PICAXE website
Some other possible sources for free ring tones are:http://www.ringtonerfest.com/
Fig.9: Rudolph Program Listing
' ***** main loop *****
if pin3 = 0 then playit
' ***** play tune *****
readadc 1,b1 'read light
REM debug b1 'optional display on screen for
' play tune depending on light level
> 200 then play_xmas
if b1 > 150 then
if b1 > 80 then play_silent
play_jingle: 'internal tune Jingle
play_silent: 'internal tune Silent
play_rudolph: 'internal tune Rudolph The Red
play_xmas: 'external ring tone tune
' We Wish You a Merry Christmas
tune 3, 4,
Next month, we’ll show you how to control Rudolph via an infrared
remote control. The transmitter also uses a PICAXE-08M chip and will
take you less than five minutes to assemble.
In addition you have to install two parts on the PC board and
change the PICAXE program.
1 Rudolph PC board
1 miniature LDR
1 miniature piezo transducer
1 miniature pushbutton switch
1 3.5mm stereo socket
1 3 x AA battery holder
1 battery clip
1 8-pin IC socket
2 5mm green LEDs (LED1 & LED2)
1 10mm red LED (LED3)
Resistors (0.25W 5%)
1 22kΩ (red red orange gold)
2 10kΩ (brown black orange
1 4.7kΩ (yellow violet red gold)
4 330Ω (orange orange brown gold)
Note: the infrared receiver (IR) and capacitor (C1) are not
required at this stage. Their use will be covered in the
infrared upgrade next month.
Also required (not in the kit)Z
PICAXE Programming Editor software (v4.1.0 or later)
PICAXE download cable (Part No. AXE026)
3 x AA alkaline cells
Obtaining kits & software
The design copyright for this project is owned by
Revolution Education Ltd.
Complete kits (Part No. AXE-107S) for this project are
available from authorised PICAXE distributors – see http://www.microzed.com.au/
or phone MicroZed on (02) 6772 2777.
The PICAXE Programming Editor software can be downloaded
free of charge from http://www.rev-ed.co.uk/picaxe/
or ordered on CD (Part No.