Hall Effect: A Hall effect sensor is a transducer that varies its output voltage in response to a magnetic field. Hall effect sensors are used for proximity switching, positioning, speed detection, and current sensing applications. In its simplest form, the sensor operates as an analog transducer, directly returning a voltage.

Discussion: - What would you use this for? - what if we connect to 3v vs 5v? - no pulldown?

- can we get jitter in readings?

- what happens if we move it back and forth very very fast?  
  (e.g., mechanically?)

hardware heuristics: - if h/w read/write has to be volatile. - hardware bugs = nothing happens. look for stupid stuff first. e.g., put wires where you don't have to count. hardware is not eternal like 0,1: use differential analysis to check if broken

		- swap sensor.
		- swap pi --- if you don't have protection, can work
		  initially, then fry.

	natural to partition project.  don't for device.
	easy to misunderstand.  have partner do too without talking
		hope to get non-correlated errors.
	
- the pdf's can have errors!   
- just b/c it 'works' does not mean it actually does.   this is very common
with dangerous voltages --- just hasn't fried pin yet.