One man’s trash…

I’ve been taking things apart now for a while, just to get a glance at their insides and a feel for what different electronics look like. Someday I might do a monster post of all the teardowns, but I figured I can at least start posting the individual items I rip apart.

Starting with this automatic trash can.

It’s got a sensor that opens it if you wave your hand over the top of the can, and some LEDs that light up when it does. It’s powered by 6 AA batteries. It’s got a switch that turns the sensor on and off, and a switch that turns the power on and off. That’s about it for user-facing components. Now let’s take a look at the inside.

The two halves of the case are secured by a bunch of Philips head screws. One is hidden inside the battery compartment (a great way to make sure you power it off before you open it). All told there are 8 of them, all identical screws so no need to worry about remembering where they go back. That’s always nice. Once they’re out, the case comes apart easily.

There’s not a lot to see inside. The positive rail from the batteries is connected directly to the toggle switch that turns the power on and off. From there, power is routed to the control board, which then supplies power to the motor. One operational detail of note – the motor is only used to open and hold the lid, and gravity is used to close it. So the control board probably only has to drive the motor in one direction.

The control board is covered in conformal coating – a nice touch, considering the case isn’t well sealed, things might be spilled on the lid, and the trash can itself is going to be a humid, icky environment. The coating should preserve the board longer against the kind of wear that the “elements” will expose it to.

The board is screwed down in somewhat of a cost-and-time-savings fashion. There are two holes for screws that have simply gone without. Two other places that could have been designed for screws instead have plastic rods from the case that guide the placement of the board. The screws on either end of the board have washers around them, to distribute their force, as they are meant to help pin the board in place against the two springs on the other side. I have no idea what the springs are for.

The bottom of the board isn’t too interesting – it has the LEDs that make up the display (when the lid is open, it has a kind of count down to when it’s going to close again) and it has the sensor. It looks like a little IR sensor to me, but then my experience with sensors is terribly limited. I could very well be wrong.

What continued to confuse me was this little board in this tiny slot that has three wires routed to it. So I pulled it out. It’s nicely labeled, with IO, VCC, and GND. It looks to me like a test board. If I were reversing this, first thing I would do is pull the plug on that and see what happened. It’s possible that the little chip on that board is sending IO somehow, but I can’t think of any reason for it to do so unless it’s for debugging (the print is tiny and my eyesight isn’t great, but it looks like a 487B2 519E4, which I was unable to find in the Googles).

Back to the main board. There are a number of transistors, both surface mount and through-hole. At least one of these turns the motor on and off. I haven’t quite worked out how the circuitry supports the behavior of the motor.

The big chip is clearly the main processor. There’s a voltage regulator, some caps, and some resistors that are probably doing some kind of voltage stepping for that chip. The other interesting parts on this board (the 8 pin chips) are an LM358 by TI (on the right) and a MX612 (on the left).

The LM328 is an amplifier. I guessed based on positioning that this has something to do with the LEDs. I’m not sure why they’d need an amp though. Could be it’s amping the voltage to drive the motor, but why locate it so far away from power, and the output to the motor?

The MX612 is a DC motor drive circuit. I don’t think it’s any mystery what that’s doing. The datasheet is conveniently in what looks like Chinese, but it does at least provide the pinout, and some graphs.

That’s all I have. Still a lot of unanswered questions, despite it being a relatively simple device.

Post navigation

Leave a Reply

Your email address will not be published. Required fields are marked *