Модель я так понимаю не летающая?
В целом самый простой вариант это микроконтроллер с жесткой программой. Либо управление с передатчика с одного/нескольких каналов, но это уже надо обдумывать алгоритм. Смена яркости программным ШИМом хоть на все лапки.
От 3В обещает работать любимая мной ATMEGA8L. В Питере можно купить здесь http://www.megachip.ru . Дешевле, чем в зажравшемся барыжном чипе-дипе раза в 3-4. Схема будет несложная, но придется программировать контроллер.
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