I guess that's what I find unclear. I'm not sure what, exactly, the display requirement is. Yes, I know he wants 10x the input for some reason, and I'm sure there are many ways of getting 10x the input frequency, I'm not sure what happens to the output, and, what the requirements of the output are, i.e. signal conditioning, waveform, etc.

The diesel engine can change speed very slowly, at best, and the unconditioned output may require considerable "cleanup" in order to be interpreted as a simple AC sinusoid, if that's what it is, but does the display take a frequency input? What is the nature of that input? Does it have to be a square wave?

In any case, there are lots of ways in which the problem can be approached, and, with a 700 Hz maximum output frequency, it should be pretty straighforward emulating a PLL frequency multiplier. If a table of all the exact integral multiples of the input frequency, as there are only 690 of them, and then a timer setup to create each possible 10x output would be adequate, wouldn't that solve the problem?

You say, "it is what they have", yet I don't see the 10x multiplier. Isn't that what he needs to create? The question lies in how it's to be applied. Doesn't that matter?

RE