Purchased the SonOff S31 with energy monitoring from Amazon for $18.99- one day delivery.
Sonoff S31 Wi-Fi Smart Plug with Energy Monitoring UL Listed, Smart Socket Outlet Timer Switch, Compatible with Alexa & Google Home Assistant, IFTTT Supporting,
Note too that this is more of a US designed switch rather than an EU designed switch.
This one has a smaller footprint and includes energy monitoring. Note that this is my first endeavor that includes energy monitoring (using MQTT).
From the Tinkerman site:
It's not that other Sonoff products are not “serious” business, but there are a number of design changes in the Sonoff S31 that make this new product a world apart. For the functional point of view it looks like a S20 with POW-powers, but they have redesigned the product completely. The result is very very interesting.
The device itself is kind of pretty, compact and robust. It has some appealing design choices (outside and inside) and the way everything fits together (see more pictures below) is great.
Aside from the male and female type A plugs, you have a ON/OFF button on the dark gray side and two LEDs. The red LED closer to the side shows the relay status and the blue one, closer to the plug is used for notifications.
Opening the case to hack the device it's not hard. The only tricky step is to measure the strength you have to apply to first remove the dark grey cap where the ON/OFF button is.
The design is based on two PCBs. The bigger one for the AC connections, AC/DC transformer and relay. And the smaller one for the the DC circuitry, including the ESP8266, an SPI flash memory and the CSE7766 power monitoring chip. It sounds like a good idea but it gets somewhat screw because they don't actually isolate AC from DC. AC is in the secondary PCB too since the power monitor chips needs access to mains. Also the distance between AC and DC traces is thinner than what would be desirable.
Note this picture is from Tinkermans site. Here will just be soldering some small wires for VCC (3.3VDC), GND, RX and TX.
IteadStudio has switched from the HLW8012 chip to the CSE7766 for power monitoring with their latests products, the S31 and the POW R2. The reason might be that the new chip by Chinese manufacturer Chipsea offers a more stable reading, according to the first tests. The good news are that both chips are pin compatible even thou the protocol is very different.
You might remember from my post about the HLW8012 that this IC uses two pins to output power and current/voltage as variable-frequency square wave. Those pins are number 6 and 7 in the SO8 package. Pin 8 is used in the HLW8012 as an input pin to select whether the output in pin 7 would be proportional to the current or the voltage.
The CSE7766 [datasheet, PDF] uses a serial protocol instead. At the moment only TX line (pin 6) is enabled. The RX line in pin 8 is flagged as “reserved” in the datasheet. Pin 7 outputs a 50% duty cycle pulse with frequency proportional to the active power, just like the HLW8012.
We all know about Itead products. They have walked a long path since the first Sonoff Basic (or Sonoff WiFi). But still, they do not provide any electrical safety certifications (ETS, UL, ETSI) with their products. They have applied for FCC, claim to be CE and comply with RoHS but EE and professional electricians will probably not install these devices. It's true the S31 is a plug-and-play device, no electrician required, but in some sense it's an “AS IS” product. You are a maker, right?
Even thou IteadStudio is improving with every design, safety distance between AC and DC traces is not met.
The POW and S31 have the caveat of being non-isolated devices. Mains are connected to the logic ground and the power monitor IC output is not isolated from the MCU. Even thou the datasheet suggests an isolated application using an optocoupler I have not seen it in the S31. So please, take all the safety precautions when the PCB is exposed.
Soldered 4 wires to board; RX, TX, GND and VCC and used new programmer. Worked fine.
Flashing
Flashing the S31 with custom firmware requires soldering some wires or a header to the pads at the edge of the small PCB. These pads expose (not only) GND, 3V3, RX and TX. Just connect them to your USB2UART programmer. Then press and hold the button (which is tied to GPIO0) and connect the programmer to your computer so it will power the board.
With GPIO0 connected to GND (that's what the button does) the ESP8266 will enter flash mode. You will then be able to flash ESPurna (or any other firmware) to the device via serial from your favorite IDE or from the console using esptool.
/home/pete# esptool.py --port /dev/ttyUSB0 write_flash --flash_size 1MB --flash_mode dout 0x00000 espurna-1.14.0-itead-sonoff-s31.bin
GUI - Power Status - connected to Christmas Tree
GUI - General Espurna Status
Sonoff S31 Wi-Fi Smart Plug with Energy Monitoring UL Listed, Smart Socket Outlet Timer Switch, Compatible with Alexa & Google Home Assistant, IFTTT Supporting,
Note too that this is more of a US designed switch rather than an EU designed switch.
This one has a smaller footprint and includes energy monitoring. Note that this is my first endeavor that includes energy monitoring (using MQTT).
From the Tinkerman site:
It's not that other Sonoff products are not “serious” business, but there are a number of design changes in the Sonoff S31 that make this new product a world apart. For the functional point of view it looks like a S20 with POW-powers, but they have redesigned the product completely. The result is very very interesting.
- Revamped case, more compact and sturdy
- Redesigned PCB, actually 2 different PCBs for main and control
- Different power monitor chip: the CSE7766 (same as in the new POW R2) replaces the HLW8012
The device itself is kind of pretty, compact and robust. It has some appealing design choices (outside and inside) and the way everything fits together (see more pictures below) is great.
Aside from the male and female type A plugs, you have a ON/OFF button on the dark gray side and two LEDs. The red LED closer to the side shows the relay status and the blue one, closer to the plug is used for notifications.
Opening the case to hack the device it's not hard. The only tricky step is to measure the strength you have to apply to first remove the dark grey cap where the ON/OFF button is.
The design is based on two PCBs. The bigger one for the AC connections, AC/DC transformer and relay. And the smaller one for the the DC circuitry, including the ESP8266, an SPI flash memory and the CSE7766 power monitoring chip. It sounds like a good idea but it gets somewhat screw because they don't actually isolate AC from DC. AC is in the secondary PCB too since the power monitor chips needs access to mains. Also the distance between AC and DC traces is thinner than what would be desirable.
Note this picture is from Tinkermans site. Here will just be soldering some small wires for VCC (3.3VDC), GND, RX and TX.
IteadStudio has switched from the HLW8012 chip to the CSE7766 for power monitoring with their latests products, the S31 and the POW R2. The reason might be that the new chip by Chinese manufacturer Chipsea offers a more stable reading, according to the first tests. The good news are that both chips are pin compatible even thou the protocol is very different.
You might remember from my post about the HLW8012 that this IC uses two pins to output power and current/voltage as variable-frequency square wave. Those pins are number 6 and 7 in the SO8 package. Pin 8 is used in the HLW8012 as an input pin to select whether the output in pin 7 would be proportional to the current or the voltage.
The CSE7766 [datasheet, PDF] uses a serial protocol instead. At the moment only TX line (pin 6) is enabled. The RX line in pin 8 is flagged as “reserved” in the datasheet. Pin 7 outputs a 50% duty cycle pulse with frequency proportional to the active power, just like the HLW8012.
We all know about Itead products. They have walked a long path since the first Sonoff Basic (or Sonoff WiFi). But still, they do not provide any electrical safety certifications (ETS, UL, ETSI) with their products. They have applied for FCC, claim to be CE and comply with RoHS but EE and professional electricians will probably not install these devices. It's true the S31 is a plug-and-play device, no electrician required, but in some sense it's an “AS IS” product. You are a maker, right?
Even thou IteadStudio is improving with every design, safety distance between AC and DC traces is not met.
The POW and S31 have the caveat of being non-isolated devices. Mains are connected to the logic ground and the power monitor IC output is not isolated from the MCU. Even thou the datasheet suggests an isolated application using an optocoupler I have not seen it in the S31. So please, take all the safety precautions when the PCB is exposed.
Soldered 4 wires to board; RX, TX, GND and VCC and used new programmer. Worked fine.
Flashing
Flashing the S31 with custom firmware requires soldering some wires or a header to the pads at the edge of the small PCB. These pads expose (not only) GND, 3V3, RX and TX. Just connect them to your USB2UART programmer. Then press and hold the button (which is tied to GPIO0) and connect the programmer to your computer so it will power the board.
With GPIO0 connected to GND (that's what the button does) the ESP8266 will enter flash mode. You will then be able to flash ESPurna (or any other firmware) to the device via serial from your favorite IDE or from the console using esptool.
/home/pete# esptool.py --port /dev/ttyUSB0 write_flash --flash_size 1MB --flash_mode dout 0x00000 espurna-1.14.0-itead-sonoff-s31.bin
GUI - Power Status - connected to Christmas Tree
GUI - General Espurna Status
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