That depends entirely on the application. If this is an embedded device that only has to relay the information to some other location or just drive an LED display and you need to save *cost* or even
*power* a chip without a timer will be cheaper and still be able to perform the function.The OP gave no indicate of needing to drive an HD44780 chip or even redlining! I did read something about using it on a bicycle!!! How many RPM will your bike do before it blows a rod?
Rick
Sometimes you have to do ugly things like write isochronous code and deal with memory banking or 4-bit processors in order to make the product affordable. Not every application can afford those expensive boutique microcontrollers with every peripheral known to man, you know. ;-) Best regards, Spehro Pefhany
-- "it's the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
Taking another angle on this: As the OP says "data acquisition system", and when logging, it is always a good idea to not lose precision.
So, you could simply decide a timer LSB (eg 10us?), and then store a timestamp for every spark. (or, time since last spark), or lower 16 bits of timer (almost the same thing), and that's a simple 16 bit capture operation.
Serial flash memory is cheap for large storages, and this would allow your PC processing to do whatever it needed, on averaging, trends, etc
-jg
An RPM meter on a bicycle? Now that would be something. I blew many rods on my bicycle when I was young ;-)
Even on a car the pulse distance measurement is really the only practical way. But yeah, we'd need more info here. I just worked on a truck RPM meter (for the really big road machines out there) and even there a 600msec update rate won't fly.
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
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