Hey all,
I'm new at the site, and relatively new at hobby electronics but I'm making my best effort here and need a bit of help. The project I'm attempting is to turn an LM2907-8 8-pin IC and a US5881 through-hole Hall Effect sensor into a variable voltage tachometer. I've accepted that counting pulses on a Raspberry Pi is impossible for a 10,000+ RPM R/C engine. I need the CPU time for other tasks on the Pi anyway. I've currently got the Hall sensor triggering a GPIO pin on the Pi, but when attempting a more complex circuit including the D/A converter I'm stumbling. I'm not trying to go for precision here. Just relative speed or zero, so the D/A converter makes sense to me. One issue I see with the LM2907 is that its minimum voltage is 6V and the Pi (and everything else I'm interfacing) run at 5 or 3.3V. How can I step this up with simplicity to utilize the functionality of the D/A converter? Some might suggest simply changing to using an IR based tach too but unfortunately this is going on a model aircraft where sunlight will constantly reflect on the sensor.
If anyone knows of an i2c solution, that's what I'm using for my IMU and altimeter, and it could tie into the same bus, but I've been researching this off and on for a year and haven't found any viable solutions. I have a Pololu Mini Maestro 24 that can read analog voltages between 0 and 5v. I already have an airspeed sensor hooked up and streaming info. If only I could create a simple circuit to measure RPM too!!!!! Any help would be greatly appreciated!! I'm on my 4th version of an etched, uv solder masked PCB to piggyback all this stuff onto a Raspberry Pi, but I don't want to make another one until I figure out how to incorporate RPM into my design. I'm more of a software guy--electronics wannabe. Digital electronics has my head spinning a bit!
-James
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