Why a cheap digital tally counter not using for other purposes? i needed a day counter for another project i was working on. So I bought a tally counter and first measured the energy consumption. That was so low that I could feed the circuit with a supercap. A small solar panel could provide sufficient energy for a very long time. The only problem was the control. How do I convert the day / night voltage of the solar panel into a signal that the tally counter increases by a number? It was a long process that resulted in this simple circuit.