I'm returning to the pool after a long absence and once again diving in over my head. I have a machine tool with two linear encoders on what amounts to the same axis. I would like to combine the quadrature outputs from the two encoders and generate a new quadrature output that is either the sum or difference of the two input signals. The outputs from the linear encoders are differential RS422 signals and I don't need to worry about the index pulses from either encoder.
Here's what I'm thinking. First each of the A and B channels from each encoder would go through a Differential to TTL converter like the MAX14890E. The output from the converters would then be fed to a pair of quadrature decoders like the LS7184N. An AVR would watch for interrupts from either of the CLK outputs of the decoders and then read the UP/DN output of the decoder. Based on the direction output, an index into a 4-state gray code table would be incremented or decremented. The output states of the A and B phases would be read from the table and then sent to a differential line driver like the AM26C31.
Is the logic there correct and does this seem doable? Break it to me gently if you don't think I have any chance of making it back to shore.