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D-type latch (with text-to-speech explanations)

D-type latch (with text-to-speech explanations) screenshot


The applet on this webpage demonstrates how to integrate the Hades simulation framework with the FreeTTS text-to-speech synthesizer. This results in a multimodal learning environment, where the interactive simulation with its animation and visualization is accompanied by context-sensitive speech output and explanations.

The circuit shown and explained here is the standard D-type latch, built from four NAND2 gates. For a textual explanation without the text-to-speech comments, please click here.


If the simulation and animation works when running the applet, but you can't hear the speech output, you have probably not yet changed the security settings of your browser's Java virtual machine. The speech synthesis in FreeTTS relies on a few operations (audio output, but also property accesses etc.) that are forbidden for untrusted applets. Therefore, to really run this applet with speech-output enabled, you might have to edit your Java security configuration file. The easiest way is to use our Java Policy Editor, which helps you to edit the security settings.

If audio output still does not work on your system, please also check the following:

If the applet doesn't work at all, and you are sure that Java is enabled in your browser, chances are that the applet simply did run out of memory. The default memory limit of 64 MBytes used for Java applets is a bit low when running Hades with text-to-speech output, because the speech dictionary, phoneme data, and audio sample buffer are all pretty large. Please check the applet usage page for information about increasing the memory limit; a value of 128 or 256 MBytes should be fine.

Run the applet | Run the editor (via Webstart)

Impressum | 24.11.06