Display Refresh Meter

In not a few cases, PC users complaining about headaches and eye strain are using a too low picture refresh rate on the PC display. The circuit discussed here measures the refresh rate using a photodiode stuck on the display screen, and indicates the value on an LC display. The instrument also allows the horizontal (line) frequency to be measured. This is achieved by inserting the refresh meter between the VGA card and the display. Both the horizontal and the vertical picture frequency of the VGA signal are then indicated on the LCD. To save current, the refresh meter is provided with an automatic shut-down function.