coffee machine water level sensor and autofill

Hi folks,

I am coffee/espresso enthuthiast. I am building a basic espresso machine from different components to suite my needs. What I need now is to control water level, and maybe temperature, although temp control is not really important for now. There are numerous posts here about water sensors, but espresso machines use a specific type, hence the question.

Basically I am looking to get an arduino to monitor the water level. There are available controllers that control water level only for about 50 usd. Since I am interested in other functionalities in the future and in safety measures, I am looking into using an arduino for the task. I am a programmer by profession, so I can learn the arduino stuff myself. But what is left is the interface with the sensors.

In espresso machines, usually they use this kind of water level sensors under boiler pressure:

Maybe later I will also use k-type thermocouple and get PID functionality also. Maybe also use some led lights to indicate if the water level is low, and if the heater is on/off.

My main question is: would Arduino interface with such sensors easily? Maybe with minimal extra components? Also, Can I use a relay to control the pump and/or heating element?

Thanks for the help in advance.

All electrical specifications are missing from your link, so there is no other answer than "perhaps".


Hi Paul,

Sorry for that. I saw earlier ad which describes it well. I am not able to locate that page.

Here is another post asking similar question, but the answer was more general. The description below is taken from the third paragraph of the first post in the thread:

"....The autofill system consists of a conductive level sensor comprising a (probably steel) rod isolated from the copper boiler by a teflon gasket which makes a circuit when the water level touches the rod. The boiler itself is grounded. A single wire then travels from the top of the probe to the control box and connects up to a comparator...."

Hopefully it gives enough information. Thanks.

Easy test, then. Connect your Ohmmeter to the probe and the boiler. Put water in the boiler and put the level sensor tip into the water. You should be able to see a resistance reduction in your meter when the probe is in the water.

If so, then your Arduino can be wired and programmed to see the same and then do something you want to happen.


Great. Thanks.

I also found yesterday that there is an amplifier for k-type thermocouple. It should help with measuring the temperature and using it as input for PID functions.

Don't forget to conform to the Hyper Text Coffee Pot Control Protocol, RFC 2324 ;)

Don’t forget to conform to the Hyper Text Coffee Pot Control Protocol, RFC 2324 :wink:

good one!

good one!

I assume you noted the date on that RFC…

Willpatel_Kendmirez: I assume you noted the date on that RFC...

Yes I did! It is the first time I know about it, though. Interesting, really.

I too am interested in building an Arduino based water level controller for coffee machines, from what I have seen by putting an oscilloscope on the water level probe and draining water there is a small amplitude square wave when the water level is in contact with the probe, when the water level drops , the amplitude of the square wave increases for 2 or 3 seconds then the relay/water pump kicks in and fills the boiler until the amplitude of the square wave goes low for a few seconds. Possibly an AC wave to avoid build up on the probe.