Decoder Lights The Way

摘要

To display the status of two digital outputs, you can simply con-rnnect an LED and its resistor on each output. You must, however, interpret, or "decode," the displayed binary code. In addition, when no LED lights, users have no way of knowing whether it means that both outputs are off, that the power is off, or that a malfunction has occurred. In some applications, including industrial and medical settings, an indicator sending an ambiguous signal would be unacceptable. This Design Idea describes a simple circuitrnthat resolves this problem by displaying four states on four LEDs (Figure 1). The operator need not understand binary coding, and, if no or more than one LED lights, it can mean only "no power" or "default."