This device allows:
The device is based on AT89C2051 microcontroller. The circuit of the device is shown in the figure below:
The indicator is connected to the PC power supply via pins Х1 and Х2. The input pin is connected to one of the HDD LED pins. The input HDD.IN controls the first LED scale (LED1-LED8). The second scale (LED9-LED16) is controlled by the input RESERVE.IN and is reserved for future use. The third scale (LED17-LED24) displays a network usage. The input pin NET.IN is connected to one of the network card LED pins. When data is being transferred over the network, the LED turns off and the voltage on NET.IN pin reduced from ~ 0V to 2V. As a result the transistor VT2 will be closed and LED25 and the LED25 will be turned on.
Initially the device didn't have resistors R3 and R4. But eperiments with a network card Compex Ready Link RE100ATX/WOL showed that:
Resistors R3 and R4 are used to set pin NET.IN to high level when the computer is turning on for correct initialization of the network card. The firmware is written in assembly language for ASEM51 compiler. The programm uses timer to control input pins and calculate activity counters which used to calculate the value of levels (ie, the number of lighting LEDs). While turning the the PC the HDD LED is turning on continuously. The firmware can detect it and reset the HDD indicator to prevent false.
Photo of the device:
On the links below you can download the circuit and PCB-layout for Eagle and firmware with sources.