Well that is certainly and old and workable solution!! When you go to purchase components you may find your self substituting some other part numbers. Clearly there are other counters that can be setup to perform the divide by 10 function. If you use the 4046's exclusive-OR phase comparator then the output of the divide by ten stage needs to be 50% duty cycle thus the 7490 counter needs to be setup as divide by 5 followed by the divide by two. If you select another counter say a 4-bit binary device and wire it up to reload so it can divide by 10 you will not be able to achieve an output that is 50% duty cycle. For a up count the Q2 output is only low four out of ten clock cycles. For a down counter the Q2 is only high four out of ten clock cycles. So if you select this means of dividing by then then you are forced into using the edge detector type of phase comparator.

On the other hand if the circuit that you use to convert the input AC signal to a squared up logic signal has distortion and ends up being a non-50% duty cycle then it would not be appropriate to use the XOR phase comparator even if your divide by ten circuit did have a nice 50% duty cycle. That would really force you to use the edge detect phase comparator in the 4046.

Michael Karas