I found two resources that were really helpful in understanding the theory: The answer: A Transformerless Power Supply (TPS), something apparently reasonably common in those tiny mains-powered devices. No transformer? No switching controller? How does this thing pull some low-voltage DC from the mains? At first glance the circuit seems like nothing special but looking deeper I realized all the usual power supply suspects where nowhere to be found. Copper-side of the PCB: a bunch of passives, a Zener diode, a bridge rectifier, a voltage regulator, a transistor, and an unknown MCU The little RX-480R PCB for the 433Mhz radio receiver Outlet PCB: look ma, no transformer! Circuit Analysis Like we’ll see a bit later the little PCB is the radio receiver for the module. One of the “components” is another tiny PCB labeled “RX-480R” mounted at a right-angle with simple 0.1″ headers. The circuit is on a single-sided PCB with a few big through-hole components on top, and a few surface-mount components on the bottom (which is the copper-side of the PCB). Detail of the prongs where we can clearly see the Hot prong not being a pass-through Visible are all the top through-hole components: a fuse, the relay, a push-button, a resistor, an X2 capacitor (yellow), two electrolytic capacitors, an LED, a spring antenna, and the radio PCB. The PCB and the prongs out of the plastic case. The outlet lets the Ground and Neutral prongs go straight through, and switches the Live (Hot) prong with a standard 10A relay. After removing these two screws the circuit and the prongs pop right out of the enclosure and we can start taking a closer look at how it works. The circuit’s PCB is held to the case by two little Philipps screws (you can see them in the photo above right above the yellow capacitor, and on the right of the blue relay). Once open we see a seemingly very simple design: a small circuit with just a few components and a couple of wires to connect it to the outlet’s prongs. A safety screw and the uncommon three-prong tip that goes with it With the right tool though it’s no different than a normal screw. The situation is made slightly more complicated by the use of three-prong safety screws, as required by the design of the power supply which we’ll talk about later on. The journey begins by removing the two screws at the back. Side view of the outlet with the on/off/program button Teardown: plug The plug has a button on the side to be able to turn it on or off manually, and to learn a specific code from a remote or to reset the programming completely. My package came with three outlets and one remote as pictured below Front of the packaging Back of the packaging Inside the box: three plugs, a remote control and its battery It’s fair to say that “Etekcity” works better for the US market. The FCC application was submitted by NINGBO BAIHUANG ELECTRIC APPLIANCES CO., a company based in China. A quick search and we can see what the FCC knows about these devices: FCC ID Q92-BH9938U for the outlet and FCC ID Q92-BHOP for the remote (although the remote at the FCC doesn’t use the same HS2260A chip). The model number at the back of the switch is 10-BH9938U. You press ON and the outlet turns on, press OFF and it turns off pretty straightforward operation! These are Etekcity’s ZAP 3L Remote Outlet Switch: a simple remote-control outlet with an on/off remote, operating via radio over the common 433.92MHz frequency (car key fobs, garage door openers, etc). The tech involved is pretty simple (mains-powered radio receiver & decoder) yet I learned plenty about power supply design, safety, and radios □ These plugs seem to still be popular on Amazon despite the proliferation of “smart” plugs with wifi and google/siri/alexa support. In this post I will be taking a look inside the ZAP 3L remote switch outlets and their remote control, roughly describe the circuits involved and look at how the communication protocol works.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |