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 increase the tally counter by one number? It was a long process that resulted in this simple circuit.
We follow the circuit from left to right. The 5V-60mA solarpanel delivers over the LDO LP2950 3V max. The voltage lost over the shottky diode BAT85 is 300mV. This charges the 10F super capacitor with 2.7V. max. The LDO MPC1703 has 1.5V out to power the Tally Counter.
The CD4093 is an ultra low power quad gate schmitt triggered NAND IC. Gate A is a comperator that makes a nice level edge with RV. Gate B makes an edge triggered pulse of 1 second. Gate C makes a 100 ms pulse at the beginning of the B pulse and Gate D at the end of the B pulse. Both, B and C pulse are connected with a 470nF capacitor to the count input of the tally.