FS-05R Mini Dimmer Firmware Replacement Issue with I/O Configuration

Question

Ciao to everybody! I follow your guide in order to replace the original firmware for a smart dimmer (no brand, FS-05R) as you can see in the attached image. I was able to do the job only removing the CB2S module from the main board: Everything seems to be fine except that it doesn't work: the...

p.kaczmarek2 · Answer

Hey, isn't it a TuyaMCU device? How does it look like from the other side?

For TuyaMCU devices, you don't get automatic configuration, you will need to paste autoexec.bat yourself.

Search for TuyaMCU dimmers here:
https://openbekeniot.github.io/webapp/devicesList.html
Here is a sample detailed teardown of dimmer with the configuration steps:
https://www.elektroda.com/rtvforum/topic3929151.html

lbelleboni · Answer

I haven't found a similar product in the list; this is why I tried to follow your guide and ask for your help.

These are other pictures of the device in question:

I do not know exactly how it works, but from the automatic configuration file I can see which are the I/O to be used (led, light_minus, light_plus, on/off button) but I have no idea how to set the dimmer setting. I'll read all the info from the link you gave me.

Feel free to ask me for other more detailed pictures.
I have another device to be flashed so I can obtain original data if required.

Thanks,
Luca

p.kaczmarek2 · Answer

It seems that you have a very unique device. I haven't seen that kind of type before. Here is the JSON:

Log in, to see the code

Still, I can see the baudrate settings there:

Can you try the following autoexec.bat:


// start TuyaMCU driver
startDriver TuyaMCU
// set TuyaMCU baud rate
tuyaMcu_setBaudRate 115200
// set TuyaMCU default wifi state 0x04, which means "paired",
// because some TuyaMCU MCUs will not report all data
// unless they think they are connected to cloud
tuyaMcu_defWiFiState 4

save, reboot, and then execute command in the web app log:


tuyaMcu_sendQueryState

Does it cause TuyaMCU to respond with some data?

I am creating multiplatform open source firmware (Tasmota replacement), right now supporting BK7231T, BK7231N, XR809, BL602, W800, W600, LN882H and soon supporting RTL and W701:
https://github.com/openshwprojects/OpenBK7231T
If you like my work, support me at: https://paypal.me/openshwprojects

Helpful post? Buy me a coffee.

lbelleboni · Answer

Ciao.I haven't yet read all the information you gave me in the previous link.Attached you can find the log from start to the command execution (supposing I did the right operation :-)I promise you to study this evening in order to be more reactive and I can be more involved in this project.Thanks,Luca

p.kaczmarek2 · Answer

Unfortunatelly it doesn't looks like TuyaMCU. IT looks like some custom UART protocol. Do you have original firmware backup?

lbelleboni · Answer

Do you have original firmware backup? yes, was attached to the first post; here again.

p.kaczmarek2 · Answer

Would you be able to restore the original firmware and do an UART capture in safe manner? By a safe manner, I mean, with all the galvanic isolation provided for UART lines, so you don't blow up your PC by shorting mains to the USB port?

lbelleboni · Answer

I have another FS-0R original module, so I should use it... but in order to be able to communicate/program the CB2S module, I have removed the module from the main board because I was not able to communicate at all.If your request is to sniff the rx/tx while the device is powered... then I have to look at the USB converter, but I'm quite sure that it is not isolated (cheaper Chinese converter). I can use a very old laptop PC, but I need to use the AC instead of battery because it's gone and the risk of burning everything is big!

DeDaMrAz · Answer

@lbelleboni

You can use ADUM1200 or ADUM1201 modules from Analog Devices, the modules are something like 2-5$ on AliExpress and they provide galvanic isolation for safe data capture and are tested to work several times now.

adolfonovo · Answer

I have two of these devices and cannot even flash them. The software cannot detect the bus.

p.kaczmarek2 · Answer

This is a common issue in TuyaMCU devices. You need to cut the RX/TX lines from the MCU in order to flash. Alternatively, you need to put the MCU into the RESET mode, if you have a datasheet for that and know how to do it.

adolfonovo · Answer

Thanks, but you said above that this is not a tuyaMCU device... don't you? How can I enter flash mode? Where is the CEN pin?

lbelleboni · Answer

HI.Unfortunately, either you find the TX and RX tracks on the printed circuit and interrupt them, or you do like me who desoldered the CB2S module from the printed circuit and programmed it.However, if you read the previous messages, I was unable to find the right configuration to make it work; I'm waiting to receive a serial converter to sniff the serial with the original firmware (and I have to hope to restore it because the second module I purchased that I left with the original firmware died for no reason). Maybe you can get the job done and help me set up.HI,Luca

adolfonovo · Answer

>>20919198I got it by interchanging rx and tx pins, maybe a silk error.Now I can erase all... but when it starts writing, I get:writing sector 0x00... writing sector 0 failed!

lbelleboni · Answer

As I wrote before, I desoldered the CB2S board in order to be able to program it; otherwise, I still have errors. Probably there is a capacitor somewhere in the same TX/RX line.

But before doing the job, did you read post #8? If you are able to "sniff" the device before changing the firmware, then I think that our guru p.kaczmarek2 can help us.

You have to sniff both RX and TX (using just the RX of your COM port) in each condition: startup, power on/off the device with the electrical switch, using the dimmer +/- (electrical switch), and while doing the job with the APP. You have to sniff the RX signal first and then do the same job, sniffing the TC signal.

@p.kaczmarek2, Correct?

adolfonovo · Answer

Yes, I can do it, but do I need some special device?... I just have a USB-TTL. Could you explain to me how to do the sniff?.... and what to do?

Another question... why am I getting this:

Failed with serial.BytesToRead 5 (expected 15)
The beginning of the buffer in UART contains 0000000000 data.
Writing sector 0x00... Writing sector 0 failed!
Writing file data to chip failed.

If desoldering will be mandatory, I wouldn't be able to erase the data also, would I?

lbelleboni · Answer

Hi AdolfoNovo,I think that we need an isolated serial port because we need to have the dimmer unit connected to 230VAC. I bought a unit in China because I have a non-isolated unit; I'm waiting for it to arrive.@p.kaczmarek2: If I understood correctly what you wrote to me, we have to log all the communication running to CB2S during each Wi-Fi command and each on/off dimmer +/- command. Of course, we have to connect just our RX signal, one time to CB2S TX signal and repeat the same with the CB2S RX signal. @p.kaczmarek2, is that correct?Are we still sure that there is another intelligent device on the board that communicates with CB2S?Best Regards,Luca

adolfonovo · Answer

Ok, I understand. Well, what should be isolated?... the adapter?... the USB? I cannot figure out why we need that because I think that even connected to 230V, the CB2S board is fed with 3.3V. Am I wrong?

p.kaczmarek2 · Answer

If you want to power from mains, the UART of course has to be isolated, there are some chips optoisolators on aliexpress.
Alternatively, you could try powering your device from USB, of course assuming that your device has 5V on the board (going to the input of LDO, to provide 3.3V for WiFi module) and try to do capture then.

lbelleboni wrote:

Are we still sure that there is an other "intelligent" device on the board that communicate with CB2S?

This is the photo that was posted:

U1 is a power supply chip, that converts mains to something like 12V or 5V, depending on the device, I don't know.
U2 looks like the MCU.
Another strong indication that there is something UART-related going on is the TX and RX pad near U2.
I think you can check with your multimeter (with the device disconnected from power, of course!) in the continuity test mode that RX1 and TX1 are connected to U2 chip.

I am creating multiplatform open source firmware (Tasmota replacement), right now supporting BK7231T, BK7231N, XR809, BL602, W800, W600, LN882H and soon supporting RTL and W701:
https://github.com/openshwprojects/OpenBK7231T
If you like my work, support me at: https://paypal.me/openshwprojects

Helpful post? Buy me a coffee.

adolfonovo · Answer

Thanks p.kaczmarek2!...

Let's see if I understood. In your alternative way, we should power on the device, and do we have to do it directly through the LDO? I can take either 5V or 3.3V from the USB-TTL adapter. What should I use?

Another question. How is the process to sniff? What is the software for that? just using putty for example?

Added after 10 [hours] 38 [minutes]:

>>20922303

I have measured continuity between U2 and TX and RX pad and TX-> pin 8 and RX->pin 1

Also, Im not be able to program with anything even qith the ol hid aplication

adolfonovo · Answer

Finally, I was able to flash the device, only unsoldering the CB2S board, as Luca said.
I have tried several configurations and none of them work.
I can't even find the Relay pin.

I think that IC (U2) has been orphaned by programming OBK separately from the board.
What do you think?

p.kaczmarek2 · Answer

As I said, you will not be able to find a relay pin, because this device works like TuyaMCU, so all control is done via U2 and WiFi module controls U2 via UART (RX1 and TX1). We need to have a capture of UART 1 traffic with original firmware to see how it's done. Then we will need to replicate this communication protocol on OBK.

adolfonovo · Answer

Thanks a lot for the quick response. Is there any tutorial to follow in order to make such UART sniffing?

adolfonovo · Answer

Hello, just a question about this, @p.kaczmarek2.

LED and button are controlled also by the PCB microcontroller? I can control by panel setting up P7 and P8
"pins": {
"7": "Btn;1",
"8": "Rel_n;1"
},

I do not know if this is a normal behavior or is important.

adolfonovo · Answer

>>20922303In reply to this question RX1 and TX1 of the CB2S are not connected to U2Regards

p.kaczmarek2 · Answer

I am afraid that we need you to draw a schematic of this device, because I am not able to understand how CB2S connects to U2. You said: You can also consider just sending this module to me so I can do measurements on side and provide you with results.

adolfonovo · Answer

Yes, of course... that's great!!!I have a brand new intact. Just linked with the Tuya app..Send me a PM with your address and I will send it to you

lbelleboni · Answer

Ciao p.kaczmarek2. Do you have some news about this device? Thanks, Luca

p.kaczmarek2 · Answer

This device is super confusing.

1. It has no LDO and no extra step down converter, the main step down converters changes mains to 3.6V and then, after one diode, we already have 3.3V for WiFi module:

2. the CB2S has incorrect silkscreen:

Correct one is:

There is some movement on TX/RX. Doing nothing:

Zoomed in:

Next packet:

Next one:

Single button press:

Zoomed in:

Hmmm 55 AA ?

Hm"

Approach	What users observed	Practical result
Flash in-circuit	Bus not detected, write sector `0x00` failed, RX/TX interference	Often unreliable
Desolder CB2S first	Flashing succeeded for multiple users	Best path to install OBK
Assume full auto I/O detection	LED/button may appear, dimming still fails	Incomplete setup
Use UART-based control at `115200`	Manual `0x30` commands worked	Dimmer became usable

FS-05R Mini Dimmer Firmware Replacement Issue with I/O Configuration

How do I configure OpenBK7231 after replacing the FS-05R dimmer firmware when automatic I/O detection does not give a working setup?

Topic summary

FAQ

Quick Facts

How do I flash an FS-05R mini dimmer with a CB2S module when the programmer cannot detect the bus or write sector 0?

Why doesn’t the OpenBeken automatic configuration fully detect the I/O setup on the FS-05R mini dimmer?

What is TuyaMCU, and how is it different from a custom UART protocol in dimmer devices like the FS-05R?

What is galvanic isolation, and why is it important when sniffing UART on a mains-powered dimmer?

What’s the safest way to capture UART traffic from the original FS-05R firmware without risking damage to a PC or USB-TTL adapter?

Which UART sniffing software and workflow should I use to log RX and TX traffic from a CB2S-based dimmer during startup, button presses, and app control?

Why do some CB2S dimmers need the module desoldered or the RX/TX lines cut before flashing OpenBeken?

How can I tell whether an FS-05R dimmer uses TuyaMCU or another microcontroller communicating over UART?

What autoexec.bat script is needed to make the FS-05R mini dimmer work in OpenBeken with toggle and dimmer channels?

How do I configure an FS-05R dimmer as a simple on/off switch with Alexa WEMO emulation and an automatic 2-hour turn-off timer in OpenBeken?

Why does an FS-05R with OpenBeken keep rebooting, showing short online time, random on/off behavior, or disappearing web access?

How do I completely reset or clear an OpenBeken device back to a clean state after a bad script or unstable configuration?

What do repeated OpenBeken log messages like 'TuyaMCU: Consumed unwanted non-header byte' mean on the FS-05R dimmer?

ADUM1200 or ADUM1201 vs powering the board from USB rails: which approach is better for safe UART capture on a CB2S dimmer?

Why does the dimmer slider reach full brightness by around 100 instead of 255, and how do non-dimmable LED bulbs affect FS-05R dimmer behavior?