Compilation of 3 previous articles with an Atmega328 running on 1.5 Volt and an adapted Led circuit around D13. Instead of an AA battery you could also use a 1.2V NiCad cell and add a solarcharger to that.
The HT7750A supposedly can deliver 200mA. The HT7750 only 100. (although the datasheets make me doubt that). All in all this DC-DC converter may be a better option
Note: There is a mistake in the circuit: the 4.3 Mhz Crystal should be a 16 Mhz