Water level sensor advice

[Marvinfly]

Hi,
I need to measure the water level inside a coffee maker tank.
I bought an 8 inch eTape sensor
(http://www.youtube.com/watch?v=c3VJPi1TeSY)
and was advised to cut it down to the size I needed and seal the end with silicone. Unfortunately this didn't work. It would have worked but the tank was still to short to use the tape.

I need another way of measuring water level over a five inch, curved, plastic surface.

Basically I'm going to use the sensor to measure if the device has water in it. This will stop the unit from attempting  a brew if it is empty. This will save the glass jug heating up for nothing and possibly breaking. It also alerts me that I can't brew via twitter. I could do this by having a variable resistor spread over the five inches.
or I could possibly have several pairs of exposed wires glued down the side of the tank. This would need to send a current through the water to detect which ones are wet. Not ideal.

Do you know of any methods or sensors that fit my needs?

Thank you.

[dhenry]

A weight sensor, or a capacitive sensor, or a light sensor, etc. would work, depending on your setup.

[pbrouwer]

Use what coffeemakermanufacturers do: use a float switch or a floating magnet and a magnet switch / sensor. If the water level drops below a certain level, the switch closes (or opens, depending on how you mount things up). You could also use a pressure switch / sensor, but given the application that might be a bit more tricky (involves drilling holes etc.), and more expensive.

Pieter

[pylon]

Maybe something like this will serve you?

http://www.seeedstudio.com/depot/water-level-switch-p-565.html?cPath=156_160

[Marvinfly]

Maybe something like this will serve you?

http://www.seeedstudio.com/depot/water-level-switch-p-565.html?cPath=156_160

I was looking at vertical floats.
I don't really want to have to cut through the bottom of the water tank because it's just one more hole onto the electronics, but it is a possibility. I need a very narrow float. I have about 25mm to play with at the bottom of the tank.
Also, if the water boils and makes the float switch, it might cut the circuit to the relay controlling the boil. But could be solved with a short timer of the connection time.

I'll think about it.
Thanks

[pylon]

I don't really want to have to cut through the bottom of the water tank

Why do you think you have to cut through the bottom of the tank? You can put this thing in from the top.

Also, if the water boils and makes the float switch, it might cut the circuit to the relay controlling the boil. But could be solved with a short timer of the connection time.

I don't understand the meaning of this sentence.

[dc42]

Is the liquid in the tank grounded (or could it be), and can you stick metal foil around all or part of the plastic tank? If the answer to both is yes, you can make a capacitive sensor. You use the sensor as the capacitor in a CMOS 555 oscillator, and use the Arduino to measure the frequency. See http://arduino.cc/forum/index.php/topic,71628.msg536307.html#msg536307 and other posts in that thread.