Instructions

44
Pulse width modulation
The individual LEDs are not only switched on and off, but also
appear lighter or darker. Sometimes the brightness increases
evenly. Therefore, you might suspect that some kind of poten-
tiometer is installed to change the current. But, actually the
LEDs are turned on and off in quick succession. If you move
the entire structure back and forth quickly, you can see light
strokes of different lengths. The length of the pulses is changed
and therefore the average duty cycle. The change (modulation)
of the pulse length gives the impression of a change in bright-
ness. This is called pulse width modulation (PWM).
23 White flashing light
The colour-change LED should now flash a white LED in
sync. To achieve a high level of brightness, a relatively small
resistance with 1k Ω (brown, black, red) is required. The col-
our-changing LED is intended to modulate the current through
the white LED. It has to be connected in series. Sometimes
the brightness of the white LED is adjusted in steps and
sometimes seamlessly. Two other LEDs are also connected in
series for comparison, but shine with the same brightness.