August 21, 2017

Miniature laser harp

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DIY Kit – Laser harp with 8051


A laser harp is a harp without strings. Instead of a bright beam, the user only needs to toggle the beam, as if
he had struck a string and still played a melody. The photosensitive resistor and the monolithic integrated
circuit STC89C52 two parts constitution. The laser beam emission tube is blocked, and the corresponding
photosensitive resistance induction resistance changes, changes of system of eight photosensitive resistor
which produces high and low potential, and the MCU reads the change of photosensitive resistance of high
and low potential, complete the operation command input, SCM according to the instruction information to
control the data transmission through the serial port, both docking the speaker’s p0^2 port and then light water
P1 port assignment, to produce the corresponding reaction.

When a laser is irradiated, the microcontroller reads the voltage of the photosensitive resistor, which is low at
this time. When no laser radiation, the microcontroller reads the voltage of the photosensitive resistor, then it
is high level. Thus, when the light of the laser is shielded, the effect of the switch can be generated in the

The frequency of the human ear can be heard from 20Hz to 20kHz, and the harp note frequency should be in
this range. Just different notes have their own fixed frequencies. Through the 52 microcontroller comes with
16 bit timer, you can produce the above audio. For example, the harp’s standard tone, La, is 440Hz. By
calculation, the half period is 1136 Mu s. Thus, the square wave of the 440Hz can be generated as long as the
jump pin level is changed in the half cycle. And then through the electroacoustic conversion element (horn),
you can produce standard tone La, and other notes are the same way.

Our laser harp features

  • there are 7 strings, when the string is cut, the buzzer corresponds to the sound level
  • cutting strings, corresponding to the string LED lit, a total of 7 LED
  • play two pieces of music stored by button
  • medium high bass switch