Hardware Reference
In-Depth Information
Figure 5-2.
VS1838B wired to the Raspberry Pi using GPIO 17
The circuit may appear somewhat daunting to students, compared to some of the
other projects in this topic. The datasheet lists several components as being required:
100 W resistor
R
1
, and capacitors
C
1
and
C
2
. Finally, there is the pull-up resistor
R
2
, shown
here as 22
k
W.
■
Note
the datasheet simply shows the pull-up as being > 20 k
W
.
If you're breadboarding this in a hurry, you can probably leave out
R
1
,
C
1
, and
C
2
.
I wired mine with
R
1
but forgot about the capacitors. If you leave out the capacitors,
R
1
is not required either.
R1
is not a current-limiting resistor here;
R
1
and the capacitors
are simply a low-pass filter designed to provide a quieter power supply to the part
(which should normally be used). But if you're soldering this up, do include all of the
recommended components for best results. Don't leave out the pull-up resistor.
R
2
is
required.
The IR Receiver
Most IR remote controls today use the 38 kHz carrier frequency on an infrared beam
of light. Even if you know that your brand of remote uses a slightly different carrier
frequency, the VS1838B may still work. The important point to realize about this part is
that it tries to detect the remote control while ignoring other light sources in the room.
To discriminate between fluorescent lighting and the remote control, it looks for this
38 kHz carrier signal. When it sees a steady stream of pulses, it can ignore the
interference.
