Application Notes - Using the Scope

Using the Scope Feature to Determine Signal Quality (registered users only)
When initially training buttons from a new remote it's a good idea to check a signal or two using the Scope feature to confirm that they're ok. But how can you tell? The ultimate test is to try to control the device with the newly trained button, but if you're having problems doing that then the scope is a built-in tool that can help you figure out what's going on. Signals differ in appearance between different remotes, so there's not a universal format to look for, but there are some obvious characteristics of a bad signal.

• Long initial stretches without pulses -- like this:

The above example is a result of placing the remote too close to the IR200L dongle during training. 

• Signal bursts containing very narrow spikes -- like this:

The above example is a result of placing the remote too far from an IR200L dongle during training.

What should a good signal look like? This varies among remotes, but here's one example with pulses that are relatively narrow but are not "spikes". Note that many remotes include an initial "shelf" (very wide pulse at the beginning) that is used for synchronization with the receiver. This is followed by the actual data, which is a stream of pulses.

The following is a similar signal scrolled to the right to reveal the start of another signal "burst". You may see this if you press more than one button on a remote during training, as we did in this example, or if you hold down the button. In this case the lone "spike" that separates the two bursts is not noise but rather an intentional flag to indicate separate command signals. This separator spike is used only internally and is never transmitted.

To show the variability of good signals, here's another example of a good signal from a different remote:

Note that the tail or separation between signal bursts can be fairly long, but the actual data for the command is conveyed by the pulses. So there should be an obvious clustering of non-spike pulses that make up each signal burst.

One last example:

The wide pulse followed by a narrower pulse (near the right side of the scope display) is a normal "repeat" command. Some remotes will send this short burst while certain buttons (like a volume button) are held down. The repeat command should always be preceded by a longer burst that represents the actual command to repeat.