Combine data from 2 tachometers “+” “-“ ?

Discussion in 'The Projects Forum' started by B F Clanton, Mar 12, 2012.

  1. B F Clanton

    Thread Starter New Member

    Mar 12, 2012
    Premise: 2 servo motors connected in such a way that one motor#2(M2) will either augment or retard the efforts of motor#1 (M1) dependant on the direction of M2. I have the tachometers (T1, T2) built, output to 4 digit-7seg display. I want to take the data from T1 and add or subtract the data from T2 depending on the direction of M2.
    Circuit: [BDC counter (74ls90)]-[shift register (74175)]-[BCD to 7seg decoder (7447)]-[7seg display] X 4
    Options: I was going to try to use a 4-bit full adder (74283) with an exclusive-OR gate (7486) to achieve the subtraction part that would be triggered when M2 is in reverse.
    Problem: The adder/subtracter is dealing with full 4 bit (1-16) and the shift register is outputting 0-9.
    Question: how would I get the a/s the carry on the rollover 9 and deal with any remainder 11-16?

    a/s Theroy: