Hall Effect/Reed Sensors

What’s a good sensor I could use? Preferably something that connects via PWM.

We are successfully using the US1881 Hall Latch. I got the units at Spark Fun and built a circuit/PCB around it. We tested it this week with a wheel spinning upwards of 5400 RPMs (FP on an AM gearbox). We put some 1/8th inch rare earth magnets on an idler sprocket. The us1881 responds well with the tiny magnets up to about 1/2 inch away.

US1881:
http://www.sparkfun.com/products/9312

Magnets we are using - small but work well with the chip:
http://www.sparkfun.com/products/8644

Thread discussing the sensor:

Feel free to let me know if you need any help with it