So, like Mike said, use the 8052 to measure the periods. Like Erik said, use a processor like the 89C51, with the PCA to make this really easy (see PCA cookbook in links) and bear in mind that the INFORMATION is changing MUCH slower than the data - so you if are cunning you can save data in your recorder at a rate like 5 Hz and get loads of storage. You only need an 8 bit record, since the resolution of a servo is pretty low anyway. At 5Hz you have 1.8 Hours of data. Even the on-board Ram on an 89C51 will hold 6 minutes of data in 4K.

Steve