design a gray code converter to drive a seven segment indicator. the four inputs to the converter circuit(A, B, C, AND D) represent a decimal digit coded using a gray code assume the only input combinations represents the digits from 0 to 9 can occur as inputs, so that the six unused combinations are don't care terms. design your circuit using only two, three, and four input NAND gates and inverters. try to minimize the number of gates and inverters required. the variables A, B, C, AND D will be available from toggle switches.