Water Level Sensor for HHO cell

[Yucca]

As MW383 says, continuity based sensors can be a bit temperamental. But as you are reading the sensor with a microcontroller I would advise going with continuity sensor just because its solid state and reliable and the micro can filter out glitches using the scheme below:

I havent built HHO system with micro but I´ve done various other work in industrial systems.

You can use small stainless fasteners through the side wall of your tank with synthetic washers. Place fasteners quite a few cm apart at fluid full level through the tank side. In sticky fluids you have to go on opposite sides of the tank.

I always read the voltage using an ADC pin if I have one available because you can tweak the HI and LO thresholds in software.

In the micro read the sensor pin once a second. If you see the pin change state HI to LO and then it holds the new state for 20 more seconds without interruption then treat it as a drop in fluid level and run the 12V pump.

Some systems use two level sensors, lower one to trigger pump start and higher one to stop the pump, but I always use one sensor and when I see a 20 sec state change I just power the pump for a preset number of seconds and then stop it.

[Draco Rylos]

My HHO cell idea didn't start off using a uC, but it evolved into using a PIC. I'm using a PIC16F690 as the heart and brains of my switching system.  I've got the logic down pretty simple

(Operation)
Upper (RA1) + Lower Sensor (RA2) = 1 Then Operation (RB6) = 1; Warn (RB5) = 0; Refill (RB3, RB4) = 0
Upper Sensor = 0 + Lower Sensor = 1 Then Operation = 1; Warn = 1; Refill = 0

(Refilling)
Upper + Lower Sensor = 0 Then Operation = 0; Warn = Flashing; Refill = 1
If Lower Sensor = 1 + Upper Sensor = 0 Then Operation = 0, Warn = Flashing, Refill = 1
If Upper + Lower Sensor = 1 Then Operation = 1; Warn = 0; Refill = 0
(End Refilling)

But I've changed how the system is set up, by swapping out the LEDs that were represented in this logic diagram with a 2x20 LCD. Port C is my LCD output, Port B is my General Outputs, and Port A are my inputs, with RA0 being my ADC port with the preset, and RA1 is the upper sensor and RA2 is my lower sensor. I have the rest of my pins pulled to ground with 10K resistors, except for my clock inputs.

[Yucca]

cool, are you going to do PWM with the PIC too?

[Draco Rylos]

No, I'm going to use ZeroFossilFuel's current limiting Pulse Width Modulator. The Power on/off will be controlled by my control circuit along with the refill valve and the pump on/off switching.

[Yucca]

That´ll work well. Have fun and good luck with it.