Automatic Litterbox Central

Today my beloved LitterFree died. Well, it is actually very ill. When I start a cycle, it starts filling up with water, but after 3 seconds already is stops filling and starts churning. Obviously with way too little water.

So I did what every LitterFree owner has to do about once a year; Take the unit apart and clean out the inside of the processing unit. I don't know what LF had in mind while designing this product, because it obviously needs this done about eacht year, but it's very service-unfriendly. Anyway, it took me about 2.5 hours before I reassembled it. Personally I don't have a big problem with reassembling it, but that's probably because I'm an engineer. My mom would probably have more problems with that. So I pluged it in and started the unit, waiting in anxiaty. But to my dissappointment the problem persistet.

Now if you have read my earlier posts, you know I was planning on redesigning the electronics inside anyway, but the only thing that stopped me from actually beginning was the idea of having to do without a working LF for a couple of weeks. So this was a good oppertunity. In the mean while I could still use the LF by adding half a bucket of water with every fill cycle.

An hour after I've put it back together, something didn't feel right. It's not a very complex machine and I knew it was measuring it's waterlevel using a miniature divers-bell, connected to a pressure sensor. The problem must have had something to do with that. While cleaning, I've had already blown out the hoses, so that couldn't be the problem. Pershaps the sensor was stuck. That was worth while to check out. So I've opened up the unit again.

I removed the hose from the pressure sensor and carefully blew into it's inlet. I could hear a soft click inside. That taught me it wasn't an analogue but a digital sensor. I took my multimeter and checked if the sensor was actually switching. It did. That left only the control panel box. If the status of a switch must be measured, some current must past through it, so some voltage must be applied to it. So I disconnected the leads to the sensor and measured for any voltage. Aha; None was present.

So I removed the control panel box and opened it up. A close inspection of the PCB revealed that a SMD resistor (R32) was missing! I had gotten so hot, that it had de-soldered itself from the PCB. Since it's about 1/4th of the size of a granule, it was impossible to find. So I reverse enginered the electronic diagram. Using my enginering skills and the datasheet of other components I discovered that R32 should have the same resistance as R31, 12 kOhm. Before replacing it, I calculated the amount of power disapated by the resistor. To my surprise it was a whopping 1.1 Watt! While these types of resistors can only have 0.25 Watt at most! Yes, they're only used for a short period of time, that is, while filling up. But if you have low water pressure, this may be too long.

The 110 Volt version may have less problems with this. They still use the resistors to 0.6 Watt, over twice as much as allowed, but it won't lead to problems as quick as 5 times as much as allowed. It's a real crappy design, not only because of that, but also because the way the pressure sensor is read out. Yeah, I know, what kind of a design do I expect from a crap box...

Be careful when experimenting, like me: Every wire inside the processing unit carries 110/220 volts! And the traces on the PCB carry mixed low and high voltages too (illegal to European laws).

Hi,

after weeks of searching, I finally became the proud owner of a litterfree. It was quite difficult, not only because they're out of business, but also because we live in the netherlands. But anyway, we've got it. We've been using it now for only 2 months, and unfortunately problems have already started. A couple of days a go, I noticed that the box leaked quite some water onto the floor. From just looking at it, I saw that it filled the box with too much water, causing it to spill. As often suggested at this forum, I opened up the unit and cleaned it carefully. The problem of letting in too much water has gone now... However, many other things go wrong: it fills the box only with very little water (for about 5 sec.) and drains and churns at the same time! Even during the churning, it adds little bits of water, but immediately starts draining it. Next, an error 2 message is displayed...
What could be wrong here??
I read you had kind of the same problem, and found out what it was, but unfortunately, I'm an economist, not an engineer, so are there any other solutions?

Thanks in advance!

Roel
(and Sam, Max & Rik, waiting anxiously for their toilet to work again)