I have recently made a model V8 ic engine and would like to build an arduino based rev counter. Pick up would be from a Hall effect transducer. But would like help with 1) the sketch and 2) how to connect to a suitable digital display.
Would appreciate any help please John
You probably want to figure out how you are going to display the number. The hardware choice will have a lot to do with the software design.
How many digits?
How much money are you willing to spend?
Do you have a particular type of display in mind? Red 7-segment displays? Graphic LCD?
You also need to know if the Hall Effect transducer is outputting pulses of 0-12V. You will need to step the voltage down to 0-5V for Arduino to read. Sensing a Hall Effect switch is as easy as sensing a button (the arduino actually can't even tell if it's a button or a Hall Effect switch). Get use some details of the sensor and what display you want to use like johnwasser requested.
Perhaps you can use a CNY-75B or similar opto-isolator and simply have the hall effect transducer on another voltage rail.
I used this technique going the other way, to drive a 12V fan at a desired rate: http://my.grumpykitty.com/2011/04/arduino-freertos-fan-rpm-video/
My input to the arduino was analog, but it seems like the CNY-75B would be generally useful for I or O. It's just a small chip that acts as a transistor but with the gate at a different voltage to the collector and emitter.
You can download a sketch for the rpm counter using a neat little timer library someone made public, and the temperature controlled fan is in C++ using FreeRTOS (not the recently posted DuinOS, and caution - I ran out of memory using it!).