Sunday, February 5, 2012

Digital display in trains

Yesterday I traveled to Mysore in Tiruchi-Mysore train. The thing I observed in Bangalore railway station was the introduction of digital LCD display on trains. Some trains had them including the one I traveled. Roghly I saw one display board per 5 bogies (not sure). This is very good move. It also shows en-route towns which train stops. This is on par with BMTC buses in Bangalore. Hope the display lasts for long time. I am really not sure their reliability during rainy days. I suppose they will be spoiled if water enters the board. Apparently no protection from water was seen. Anyhow I welcome the new facility by raiways. Hope this will last long. And as always here is the picture. (bit obscure though)


The picture was taken with (1/25)s shutter. With (1/50)s of shutter, the photo was not proper with some part of display not showing up. Then thought for while and recalled the LED animation we were covering in microprocessor lab. Basically the display has refresh rate and shutter is how fast you capture the picture. Hence if the shutter is more than the refresh rate obviously the photo will not contain some part of LCD display. Consequently you need to take picture which is slower than refresh rate of the display. From the above experiment the refresh rate of train's LCD display board is

50Hz < refresh_rate <= 25Hz [Small lab experiment :)]

Sorry I am not expert photographer. There may be better way of doing this. You can have similar experiment by taking snap of your desktop or laptop screen [of-course being powered on :). Seen in CRT displays though]. Usually refresh rate of displays is between 50 to 75Hz. So in order to have proper picture, you need to adjust shutter less than refresh_rate. Try it out :). Any corrections to explanation is welcome

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