1 字符游戏 morse
在 FreeBSD 的源码中有一些字符游戏，位置是 /usr/src/games，其中一个是 morse，它可以把字符串翻译成莫尔斯码，也可以把莫尔斯码翻译成字符串。不仅如此，这个程序还可以驱动外部设备，把莫尔斯码发送出去。
2 LED 上的 dit 和 dah
在 morse 的 manual page 里有这样一段话：
Using the -d flag, it is possible to key an external device, like a sidetone generator with a headset for training purposes, or even your ham radio transceiver. For the latter, simply connect an NPN transistor to the serial port device, emitter connected to ground, base connected through a resistor (few kiloohms) to RTS, collector to the key line of your transceiver (assuming the transceiver has a positive key supply voltage and is keyed by grounding the key input line). A capacitor (some nanofarads) between base and ground is advisable to keep stray RF away, and to suppress the minor glitch that is generated during program startup.
就是说可以把输出信号加载到串口的 RTS 脚上面。
LED 阳极接串口的第 7 脚 RTS，阴极通过一个 4.7k 的限流电阻接到串口第 5 脚 GND。
LED 按照 Morse 码的节奏闪烁。
