设计一个高低电平信号的测试电路，功能如下：

1．　　测量范围：低电平UL<0.5V ，高电平>5V 。

2．　　用高音表示被测信号为高电平。

3．　　用低音表示被测信号为低电平。

4．　　当被测信号在0.5V～5V之间时，不发出音响。

-Design a test circuit high and low signal, the following functions:

1. Measuring range: low UL <0.5V, high level> 5V.

2. Treble represented by the measured signal is high.

3. With bass indicates the measured signal is low.

4. When between 0.5V ~ 5V when the signal is not audible.