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DIY Kit 104 MUSIC BOX ENGINE
DIY Kit 104 MUSIC BOX ENGINE
This kit is the electronic equivalent of a mechanical music
box. It has a range of tunes. It is activated by light falling
on a light dependent resistor (LDR) sensor. The kit can be
placed anywhere that you want a tune to play when light
falls on it: a cupboard, music box. Or there could be some
applications where the LDR is replace by a switch or a
push-button.

How it Works
The music generating IC forms the heart of the project.
Two ICs are provided in this kit. M3481 contains 8
Christmas songs. M3485 contains 5 popular tunes:
Hawaiian Wedding Song, Try to Remember, Aloha Oe,
Love Story & Yesterday.

When light falls on the LDR the music IC is enabled by
the positive potential appearing on pin 2. The sensitivity
of the LDR can be changed by varying the value of the
100K in the SIL connected to pin 2. A tune is selected by
pushing the PCB-mounted tact switch. The jumper J1
determines whether the selected tune will play
continuously or will cycle through all the tunes available
in the IC. The musical pitch is determined by the resistor
R1. Decreasing the value of R1 lowers the pitch, and each
tune takes longer to play. The RC network at pin 7 shapes
the sound. The speaker is driven by a complementary pair
of transistors driven by the IC. Negative feedback is
provided by R3 to stabilise the DC voltage at the emitters
of Q1 & Q2.

Jumper J2 selects whether or not a tune stops immediately
the light onto the LDR falls, or it plays right through to its
end before stopping.

In the resting state the circuit draws about 50uA, and
about 20mA when it is operating. So there is no need for
an off/on switch.

Construction
Check the components provided against the parts list. It is
generally best practice to add the lowest height
components first: the resistors. To keep the PCB area
small one of the resistors is placed under the IC. Make
sure to get Q1 & Q2 correct. They are not the same. One
is an NPN transistor while the other is a PNP type. Also
make sure to get the electrolytic capacitors around the
correct way.

The LDR has long legs so you can mount it at the ideal
distance required for your application. The LDR can go in
either way around. Finally select the IC you wish to use &
push it into the IC socket the correct way around.

Testing
Once the battery is connected the kit should immediately
start to play a tune. If not check that all the components
are in their correct positions, especially Q1, Q2 and the
electrolytic capacitors. Check the solder connections.

Reference
This project was reviewed in Electronics Australia,
October 1996.



The SIL was added January 2002 after the IC
manufacturer changed the specification of the ICs and
more pull-down resistors were needed.

See out kits at

http://kitsrus.com

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PARTS LIST
Resistors 5%
6R8 ............................................ R4 R6......................2
33K............................................ R7 ...........................1
68K............................................ R1 R8......................2
100K.......................................... R2 ..........................1
330K.......................................... R3 R5......................2
100K SIL 5P4R resistor network................................1

4.7uF ecap ................................. C4 ...........................1
100uF mini ecap ........................ C1 C2......................2
68nF ceramic ............................. C3 ...........................1
2 pin header ............................... ................................2
Jumpers...................................... ................................2
Mini push-on switch .................. ................................1
LDR........................................... ................................1
16 pin IC socket......................... ................................1
M3481 music IC........................ ................................1
M3485 music IC........................ ................................1
BC548 ....................................... Q1 ...........................1
BC558 ....................................... Q2 ...........................1
Kit 104V2 PCB ......................... ................................1
3V battery snap.......................... ................................1
8 ohm speaker............................ ................................1 DIY Kit 104 MUSIC BOX ENGINE