After consolidating my first project, a temperature/pressure/humidity/sensor, I'm working to integrate it on a bigger project, a full shield ready for making an engine test bench.
On my ArduinoUno I have: A0 & A1 reserved for thermocouples reading after two AD595 to linearize output of K. Thermocouples read cylinder head temp. & exhaust gas temp. A2 & A3 reserved for torque & thrust load cells after INA125 signal conditioner A4 & A5 I2C pins reserved for barometric sensor.
D0 & D1 are free, I'm sending serial data via USB so they couldn't be used, am I wrong? D2 "start data acquisition" button D3 "stop data acquisition" button D4 humidity sensor D5 to D10 are reserved to LCD D11 is the RPM signal input D12 is the "propeller blade number" switch, they could be 2 or 1 depending on formula
the code, which starts to be a little HEAVY to run, makes me think that I couldn't make an RPM counter like the one described in the playground. In fact, being it a small model engine for an airplane, I would read propeller passages between IR led and phototransistor, 30000 RPM for two blades of the propeller will be 60k pulse per minute, or if you prefer 1khz. The other case is an engine running up to 40k RPM but with a single blade propeller. If my program will took even if only 1 ms to run, it seems to me that reading won't be accurate, Arduino-based RPM counters that I've seen on the net are intended up to about 5k RPM, while I'm up of one order of magnitude! I thought I won't be able to recognize proper signals, so initially I thought to make a mechanical device, such as a 1:10 gear reducer or an optical chopper, but these two aren't solutions easy to follow and realize at home, and even not so easy to integrate in my own shield! ...plus I have to connect phisically one of these devices with propeller hub, one more problem...
So, my question: would using a "binary counter" like 74ls393 be a good solution for downsampling input frequence of a 16x / 32x / 64 factor? would it recognize the dirty signal from phototransistor or would exist a better solution (e.g. something with a 555 timer, but I have no idea where to start with the circuit!)?
Many thanks for the attention @ my loooooooooooooooooooong post!