This instructable describes replacing the Cat Genie plastic sensor with an electronic sensor. The plastic Cat Genie sensor tends to get dirty very easily and causes the unit to make the annoying three beep error, as well as several other problems.
When the sensor gets dirty, not only do you get the three beep error, but many times the unit will not fill the bowl with water all three times causing extra stinkiness during the drying cycle (a great urine aroma). Also, since the unit thinks there is still water in the bowl it causes extra strain on the draining motor while it continues to try to drain. I have smelled the motor after a cycle and it doesn't smell like it's happy about all the extra work.
So, let's look at the sensor to see how it works. It is two plastic rod pieces connected by a small plastic junction at the bottom. The rods act like fiber optics, and the junction acts like a mirror. There are two 45 degree angles in the junction part, and these cause the light coming down one side to be reflected back up the other side. When water is in contact with this part of the sensor, the mirror effect of the plastic is negated and the light does not get reflected back up.
As long as we provide a changing IR light source to the Cat Genie's sensors (there is an IR emitter and sensor pair on the bottom looking down into this plastic sensor), then we can source it with data from an external water sensor.
Step 1: Design of the Electronic Water Sensor
There are many ways to sense the level of water in a tank, but I wanted something with no moving parts to get stuck, get dirty, etc. A simple solid-state electronic sensor would be best. After some google searches for electronic water sensor circuits, I found some ideas on how to best implement a water sensor circuit.
After experimentation on the breadboard, I found a good working solution using a Darlington Pair of transistors to provide a changing voltage to two other transistors, which then either light the IR and green LED, or it lights the red LED. This gives the user an indication of the state of the sensor, it will turn from green to red water hits the probes we install.
Below is the schematic of the sensor (credit to 2cats2dogs from litterbox-central.com for the schematic) and a picture of my prototyped board. Notice in the schematic that the IR LED is wired backwards, make sure to wire it correctly. I will fix this in a later version of the schematic. The resistor values are hard to read, so I will add notes for them. All transistors are 2N2222, CORRECTION: they are NOT 2n2222A, it probably doesn't matter though. The red/green wires go to the IR LED, the black/white wires go to the probes, and the two black wires go to a 12 volt wall wort transformer.
Step 2: Water Sensor Probe Install
First, lets create the sensor probes and mount them. The first sensor probes I made just used the copper wire to make contact with the water. This turned out to be a BAD mistake. The copper corroded after just a single day and the next day the unit kept filling with water because the wire wasn't making an electrical connection with the water anymore. It didn't overflow, but it was surprising.
It is VERY important to use something other than the copper wires for the probes. I chose to use stainless steel screws from Lowe's. They have been in there for a little over two weeks and are still just as shiny, no corrosion problems at all. Attach your probe wires to a pair of these screws as seen in the picture. Then you need to mount them inside the bowl. I mounted mine under the litter bowl, duct taped to the outer portion of the base unit. This location should avoid the majority of the poopy water seen in the hopper so they should stay cleaner here. It is important to tape them to where the bottoms of the screws are at the regular fill water level. (If you cannot tell where your CG normally fills, you can estimate where it needs to go with your litter bowl, the line on the litter bowl where the plastic turns from white to gray is the typical fill level).
I have an idea for a better mounting method, although this method seems to work just fine. A better method would be the small square sticky mounts used for wire ties, should be available at Lowe's. Wire tie the screw into two of those and stick those on there, would be a cleaner looking install.
Whatever method you use, make sure there is plenty of screw sticking down past your mount. If it is too close, or even flush with the mount, then water will remain on the mount maintaining contact between the probes even when the bowl is starting to empty.
Step 3: IR LED Install
It is important to make sure you put the IR LED to one side of your cut up pink eraser. Then mount the IR LED to the side farthest away from the drain of the unit. That is where the head unit's IR sensor is located. If you put it in the other way, it probably won't work.
Step 4: Completed Install
You should not experience any more three beep errors. Really, the only way this would fail is if your stainless steel probes corrode over, which is possible but would probably take a long time. Or, if your mounting method failed and became unstuck from the wall of the base.
I have a video of my board operating on YouTube, just search Cat Genie three beep.
Hope you enjoy.