Hardware Reference
In-Depth Information
Dump Mode
When the
-d
option is used, the program runs in
dump mode
. In this mode, the program
will report level changes on your selected GPIO pin:
$ ./irdecode −d
Monitoring GPIO 17 f or changes :
30524.573 1
4.628 0
4.322 1
0.696 0
1.555 1
■
By default,
irdecode
dumps out a 1 level when the carrier is present. to invert this
to match the GpIO level, use the
-n
option.
Tip
The left column of numbers is the time in milliseconds, prior to the level change.
The number in the right column shows you the level of the GPIO input after the change.
In this example, the first event took a long time before it changed (I was picking up the
remote). The next change to low (0) occurs only 4.628 ms later, and so on.
This is a good format for getting a handle on the average pulse widths. From this
output, you should see pulse widths centered about certain ranges of numbers.
Each line reported is a signal change event. Either the GPIO pin changes to high, or
it changes to a low level. When reporting changes, therefore, you should never see two or
more lines in a row change to a 0, for example. The reported level should always alternate
between 0 and 1.
If, however, you do see repeated highs or lows,
this indicates that the program has
missed events
. Events spaced closer together than about 150 μs are not likely to be seen on
the Raspberry Pi. Noise and spikes can also cause these kinds of problems.
Gnuplot Mode
Dump mode is great for analyzing pulse widths but it isn't very helpful if you want to
visualize the waveform. To produce an output suitable for
gnuplot
, add the
-g
option:
$ ./irdecode −dg
Monitoring GPIO 17 f or changes :
31337.931 1
31342.528 1
31342.528 0 4.597
31342.528 0
31346.860 0
31346.860 1 4.332
31346.860 1
