Hacking a Digital Photo Frame as a World Clock

So, exploiting these ideas I hacked a Kitvision digital photo frame.  Cut each of the RGB lines on the board and inserted switches (74HCT4053).  Hooked it up to an AT Mega 328P microcontroller running code derived from Peter Duffett-Smith’s Practical Astronomy with your Calculator and therefore calculated the daylight terminator across the Earth that matches a photograph of the Earth displayed on the frame.  By cutting some of the RGB signal at the right moments you get the following :

Image

The trick is to do the calculation during the flyback period, and use interrupts to do the time critical cutting of the picture.  The AT Mega has no trouble keeping up – the quantisation of the jagged terminator line is however the timing fidelity driven by the clock.

I did this in 2010.  I have forgotten some of the details – I think it was cutting the R of the RGB that got the impressive night-time effect.  I also got the eclipse shadow calculations working on a PC but was having trouble shoe-horning that into the AT Mega’s 32k code limit, so left it at that point.  This may inspire someone else.

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