Voting is a responsibility, not a privilege. We need to increase voter participation, so that all voices can be heard. However, that is considerable backlash to making voting mandatory (mostly from groups that already have high rates of voter turnout).
My preferred approach is a voting tax credit- say, $50. Voting verification would be provided by state election boards and transmitted to the IRS.
Offset that tax credit with an across-the-board $50 tax increase, and the only people penalized are those who stay home on election day or don't use absentee ballots.
There, that solves the problem without using that nasty word "mandatory."