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Originally Posted by Justin Stiltner
All,
I am currently looking at the LM2917 frequency to voltage IC as a solution, it uses an variable reluctance(hall effect?) sensor to read magnets, or ferrous materials and based on some capacitor and resistor values of your choosing outputs a voltage proportional to the frequency. If I can get the circuit working, this will be the ideal solution in my mind, all you would need to do is read the analog input that it is connected to. If someone with more electronics experience than me wants to look at the data sheets, etc. for this they can be found here
http://www.national.com/ds/LM/LM2907.pdf
I also wonder if one could use optical pickups instead of the magnetic sensor as I have a few of those already, and they seem to be very reliable.
Looks like I'm off to the electrical engineering instructors office tomorrow. |
Justin,
I have tried most F/V converters available in the market for a project a while ago. Those are pretty neat devices, but I'm afraid you will not have a very good performance.
It's tricky to adjust the circuit for the correct voltage and real resistors and capacitors will not be as precise/stable as you'd want them to be. If you read a bit into the workings of those converters, you'll find out most of them work with an integrating capacitor. The output voltage will have some ripple, inversely proportional to the capacitor value. This ripple will affect your readings, and filtering it out in software will result in a code that is slower and more complex than using interrupts. If you use a big capacitor, you'll introduce a phase lag that may render your sensor impractical.
That said, I think a Banner sensor with a small piece of retro-reflective tape will be more than enough for your application (that's what we'll be using), and Kevin Watson has provided us code that works without even needing modifications.
If you still want to try the F/V thing, I suggest you use the Analog Devices AD650 or the Texas/Burr Brown VFC320. You can get free samples on both of those, and they're much better than the National IC. The AD650 is a
very good piece of hardware and, to get a decent result, that's the one I'd use.
