40-pulses Monoshot (200ms/1A) design_help

Help me to design a Monoshot with the following specifications

1. 200ms pulse width
2. Magnitude 0.5V steps in 0-20V range (total 40 pulses). That is 0,0.5V, 1V, 1.5V,......,19.5V & 20V.
3. capacity to drive maximum 1A load.

5Hz oscillator, driving a Modulo 40 binary counter, driving a DAC, driving a power amplifier.