[CB2S/BK7231N] RR620W dual flush relay offering energy metering

Hello, today a gadget similar to the one discussed in the past ZN268131 , but distinguished by the fact that the buttons (relays) support two and additionally have voltage, current and power measurement based on the BL0942 system. I will present here the inside of this gadget, the procedure for changing its firmware and its configuration in the new firmware.

Buying the RR620W
The RR620W is very popular in the network. You can find it both in stores with shipping from China:

Parameters according to the Chinese:

Quote:

Input Voltage	100-250VAC, 50/60Hz
output voltage	100-250VAC, 50/60Hz
max. load	5A / Gang
wireless type	Wi-Fi 2.4GHz
App Name	Smart Life or Tuya APP
dimensions	47mm*48mm*23mm
works	with toggle wall switch

As well as Polish sellers:

We already see the inaccuracy here - the Polish seller summed up the current of both channels and gave 10A instead of the actual 5A . Let's read on:

Even on the housing there is 5A ...
Dimensions, assembly:


Set contains:

The product is also described on the Blakadder website as built on the basis of WB2S (WiFi module based on BK7231N):

Will our copy also have WB2S? Let's check.


Kit contents
Importers/resellers of this product are even able to order packaging and instructions in Polish, which is rather a plus, but it is still worth remembering that it is still the same gadget as I showed on Aliexpress:

Kit Contents:

Magic pink box:



A short test with the Tuya application
Applications of this type have already been discussed, so now briefly:

What do we see here?
- the application has a translation, but it is not complete (when setting the buttons there are names like "dp_relay_status", "dp_switch_type")
- there are two separate relays, but the power measurement, etc., is common for both together
- you can specify the memory of relays (default state after reboot or remembered previous state)
- you can specify the type of connected button (dp_switch_type_flip - changing the state of the bistable button changes the state of the relay, dp_switch_type_sync - the state of the relay reflectsbutton state, dp_switch_type_button - monostable button, pressing switches the relay)
- of course, there are also scenarios, timers, calendars, etc., and even random switching

The interior of the RR620W
The case is latch only. Inside, the elements are quite tightly packed.

There is CB2S, which is basically a newer WB2S, but on BK7231N and not BK7231T.



There are two relays, of course, both are WRG RC-105DM1, each powered by 5V, 5A/250VAC. These 10A sellers are misleading....
At the input there is a varistor, a simple filter made of a choke and two 4.7uF 400V capacitors:


There's no flyback power supply here, it wouldn't fit here, but there's no simple capacitive dropper either. Here is the step down converter, you can see the coil from it:

But first, BL0942 - it's a voltage, power, etc. measuring device with UART interface:



UART is used here - it is connected to RX1 and TX1 from CB2S.
Varistor:

Now the bottom of the PCB:

KP3210SG is a power supply system:

Catalog note:

Apps:

Small items, including transistors for controlling relays and their protective diodes (so-called "free-wheeling diode").

What is connected where? Later.


Firmware change procedure
This product uses CB2S, which is BK7231N. You can change the firmware to cut it off from the cloud and, among others. pair with Home Assistant. I uploaded my project to him:
https://github.com/openshwprojects/OpenBK7231T_App
Personally, they prefer to desolder the entire module with a braid and flux, and then power it with 3.3V and connect only RX and TX (except ground and power) and program it with your tool:
https://github.com/openshwprojects/BK7231GUIFlashTool
I reboot by turning off the power.
This is what the pads look like after removing the binder with a braid:

And after removing the module:

The module before soldering the wires, but already with the binder on the pads:

The cables are:

Ready programming system (LDO 3.3V TC1264 and 5V derived from USB):


And after programming - while soldering the module:


Pin configuration and board analysis
And most importantly - here is my PCB development:

All sensible CB2S IOs are occupied. Even the ADC pad is a button, which here is a single one. The relays are on P7 and P24. Single LED on P26. BL0942 is on this UART port, which is for programming, on RX1 and TX1. The switches are on P8 and P6.


An essential complement
Two issues remain to be clarified.
First - how SW1 and SW2 work, but that was discussed here:
ZN268131 WiFi Smart Switch that allows you to connect a bistable button
Second - calibration of BL0942 after changing the firmware, it was discussed here:
Electrical socket with energy measurement LSPA9 - we program our own firmware


Summary
It's not bad, quite an interesting product, I haven't described this type of relay (double) with energy measurement yet. The interior is not too poor either, there is even a varistor, although these relays could be for a higher current.
This is where I have the first small complaint - does the seller really think that adding up the current for both relays and giving 10A instead of 5A is a good idea?
The second complaint would be these incomplete translations. It's supposed to be in Polish, but the advanced features are no longer translated in the Tuya application.
I was also a little surprised at first by the lack of a fuse resistor, but I assume it's one of the surface mount ones.
Uploading only OpenBeken and cutting off from the cloud went without problems. All IO roles in the topic are listed. Just configure.
The price is quite high, but acceptable, especially for this energy measurement. I won't complain too much about it. Interestingly, the prices in Poland and abroad are similar.
is it worth it? I'll leave the decision to you. Certainly, open programming for the used WiFi module from the inside is already available and fully supports this product, so you don't have to worry about problems with the manufacturer's cloud.