Connecting a washing machine water level sensor to a microcontroller

[dinushka95]

Hello
i am  trying to connect this water level sensor from a washing machine to microcontroller.
when the water level increase the pressure inside the sensor increase causing a ferrite to move-up inside a coil.
the pins on the 2 side are connected to the coil and 2 capacitors are connected from them to the middle pin. i think the middle pin is the sense line.

P.S - a label on the sensor says 5v DC

1) how it works (capacitance or resistance)?
2) how to connected it to a microcontroller?

[mikerj]

It works by changing the coupling between the two halves of the coil.  This looks like a half bridge LVDT or Linear Variable Differential Transformer.

[SeanB]

Refer to the attached page 30. The water level sensor is used as a LC oscillator, and the frequency is measured by the MCU. Easy to build the oscillator using a 4069 hex buffer.

[dinushka95]

thank you...  very much....

[aargee]

It's always good to try to analyze and understand the circuits that you remove parts from before you strip salvage parts from a board, it saves lots of headaches about 'how the hell did that work/interface/etc'. Even helps you to ID MOVs and capacitors as like for like when their writing is sooo darn small/feint/uninterpretable.

No that you salvaged the sensor in this case, of course. The Fisher and Paykel washing machine we have uses that very technique and I think uses a 4096 as the oscillator as well.