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Tools and Materials for Arduino
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The IR TX should be modulated and an IR RX module should be used. This will take care of sunlight / heat issues.
You can also use a direct switching replacement for the 7805. It is the "oki-78sr series" of switching regulators. I have used them and they do cost a bit more but work well.
Well... the joule theifs output is switched as well. Not steady state. But, you could try replacing the Ni-Cd battery with the super cap.May work great and might have to give it a try.