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

Ok, so we know how to interface with the Cat Genie.  Provide an IR LED that can shine IR light into the CG's IR sensor and you are home free.  Now we just need to design our own sensor that will be resistant to dirty (poopy) water.

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.

<p>What do you use for probes and where do they go?</p>
Can someone tell me the resistor values? I am having trouble reading the schematic. Thanks!
<p>If you pass your mouse cursor over the resistors on the instructable's page schematic, it will show the various resistor values. It did for me anyway. I'm using firefox.</p>
Hi so I would like to buy one of these if I could. I couldn't find it on eBay so. ... if you could please please please contact me at mrosecowan@gmail.com I would be so grateful!
<p>I would also be interested. I'm fairly handy but I haven't worked with electronics in many years, and I'd rather just buy a little kit I can put in than get out the soldering iron and source diodes and such. Please email me at isaiaht@gmail.com with a price!</p>
I would really like to buy a premade kit that i just hook up my box. I looked on ebay but nothing is available. Please email me at tammy@dunn.rocks if you are able to make me one.
<p>I installed this sensor the day I installed the CG120. I have never had a problem with the box and I only take it apart and clean it once a year! </p><p>I built it into the cartrige genius so I don't have to worry about refills.</p><p>With those two mods, the CG120 is absolutely hassle and trouble free!</p>
Awesome hack! Just finished this today after weeks of false 3 beep errors and it works perfectly. Thank you for great instructions. My only comment is that the circuit diagram is rather difficult to read (low resolution). A better image would help a lot.
This thing works great, no more beeping! I had most of the parts when I started, but had to but the IR LED. Found them on E-bay, bough a bunch 50. So if any one needs them, 3 for a buck, and they include the resistor for 12v. Shoot me an e-mail and I'll instruct on how to get. mikelu53@yahoo.com And thanks again ku4zs for a great idea.
Did the IR LEDs come from China? Sounds like the same place I have been ordering mine for the kits I sell on ebay. They work great and at a great price. Glad to hear that your board is working good. I have sold probably 50+ kits and everyone has had great success with them. I don't know how many have made theirs from this instructable.
I'm having trouble with this...I have everything wired according ot the schematic but when i plug it in both LEDs light and it doesn't matter what the probe wires are doing.<br /> <br /> I also don't understand what J2 is and why pin 1 goes to ground?
I would check the collector of the two transistors connected to the probe (the collector is the side of the transistors that are wired through a resistor to power).&nbsp; From there to ground, you should read +15 or so volts when probes are out of water, and it should go to zero with probes in the water.&nbsp; If this works, then check to make sure you installed resistors between the bases of the other two transistors and the collector of the probe transistors.&nbsp; I&nbsp;have ordered some etched PCBs and will be selling a premade kit with factory etched boards soon, check ebay.<br /> <br /> Also, pin 1 of J2 is the ground connection.&nbsp; You will see 4 other ground points, some on transistors and I think one on an LED.&nbsp; Pin 1 is connected to these.
salut a tous! j'ai un cat genie en france qui fais 3 bips, vous pouvez m'en fabriquer 1 detecteur d'eau electronique et je vous paie avec paypal. mon catgenie pendant son cycles au 2eme ou 3eme lavages il prend l'eau quelque seconde et ne prend plus l'eau. voi&ccedil;i mon mail: <a href="mailto:missolivia75@ymail.com" rel="nofollow">missolivia75@ymail.com</a> cordialement a tous.s'il vous plait car sa fait 6 mois maintenant que je suis obliger de rajouter une bassine d'eaux.

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