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[BK7231N/CB3S] Mhcozy TYWRA-RF Relay Module (Dry Contact) Configuration & Setup Guide

wassimsarghini 5925 20

TL;DR

  • Mhcozy TYWRA-RF dry-contact relay module with a CB3S chip is the target of this BK7231N/CB3S configuration guide.
  • The relay module was flashed successfully, and a ready-to-use config is shared to save setup time.
  • Brand: Mhcozy; model: TYWRA-RF; chip: CB3S.
AI summary based on the discussion. May contain errors.
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  • Hello everyone,

    First of all thanks to the community.

    I flashed a relay module (dry contact) that uses a CB3S chip

    Brand : Mhcozy
    Model : TYWRA-RF

    I just wanted to share with you the config, in order to save time

    Here is the config:

    [BK7231N/CB3S] Mhcozy TYWRA-RF Relay Module (Dry Contact) Configuration & Setup Guide

    Code: JSON
    Log in, to see the code


    hope this helps someone

    Greeting

    Cool? Ranking DIY
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    About Author
    wassimsarghini
    Level 1  
    Offline 
    wassimsarghini wrote 1 posts with rating 3, helped 1 times. Been with us since 2023 year.
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  • #2 20801332
    xinetic
    Level 1  
    Posts: 1
    Rate: 1
    Yes thnx this wil help, but now it is just a wifi controlled relais, how can i learn a new RF remote control?
  • #3 21308294
    fitor
    Level 9  
    Posts: 11
    Rate: 1
    xinetic wrote:
    Yes thnx this wil help, but now it is just a wifi controlled relais, how can i learn a new RF remote control?


    Hi, did anyone solve this problem?
    Thanx
  • #4 21308412
    divadiow
    Level 38  
    Posts: 5184
    Help: 445
    Rate: 912
    are you sure RF matching must be done through software? I notice the manual only makes mention of the app method, but my experience with the switches I have with RF capability is that a long-push of one of the button also does the same. Perhaps this is also true of this device?
    Attachments:
    • TYWRA-RF-User-Guide.pdf (476.39 KB) You must be logged in to download this attachment.

  • CB3S dump with Tuya relay and RF pin mapping

    #5 21308431
    fitor
    Level 9  
    Posts: 11
    Rate: 1
    Hi, I have the instructions manual. But xinetic mentioned that the RF transmitter cannot be learned after flash, so far I relay not flash because I want to keep the RF function. I will try to pick up the Tuya config and will see.

    Dodano po 3 [godziny] 33 [minuty]:

    Hi, i made dump, the result is similar to that from wassimsarghini.
    Identifikation of ICs:
    MB10F rectifier
    XL1509  DC BUCK step-down
    RFE2740  ???
    ?? one without label
    Module: CB3S
    JSON+text:
    Code: text Expand Select all Copy to clipboard
    {
   "rl1_lv":"1",
   "on_off_cnt":"10",
   "onoff_rst_m":"0",
   "led1_pin":"9",
   "onoff_clear_t":"6",
   "rand_dpid":"42",
   "net_trig":"4",
   "netled1_lv":"0",
   "jv":"100",
   "onoff_rst_type":"2",
   "total_bt_pin":"6",
   "nety_led":"0",
   "total_stat":"0",
   "reset_t":"7",
   "netled1_pin":"8",
   "remote_add_dp":"49",
   "remote_list_dp":"50",
   "net_type":"0",
   "inch_dp":"44",
   "module":"CB3S",
   "ch_cddpid1":"9",
   "onoff1":"14",
   "init_conf":"38",
   "led1_lv":"0",
   "zero_select":"0",
   "onoff_type":"0",
   "series_ctrl":"0",
   "total_bt_lv":"0",
   "cyc_dpid":"43",
   "remote_select":"0",
   "ch_num":"1",
   "rl1_pin":"24",
   "netn_led":"0",
   "ch_dpid1":"1",
   "crc":"85"
}

Device configuration, as extracted from Tuya: 
- LED (channel 1) on P9
- Pair/Toggle All Button on P6
- WiFi LED on P8
- TglChannelToggle (channel 1) on P14
- Relay (channel 1) on P24
Device seems to be using CB3S module, which is using BK7231N.
And the Tuya section starts, as usual, at 2023424


    Could you confirm that this configuration enable RF code learning?
    Attachments:
    • readResult_BK7231N_QIO_Tywra_2024-18-11-19-31-41.bin (2 MB) You must be logged in to download this attachment.
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  • #6 21309043
    fitor
    Level 9  
    Posts: 11
    Rate: 1
    I flashed the relay successfully, it connects to wifi but cannot connect to the web interface :-(
    It's there way to reach settings in another way?
  • #7 21311074
    fitor
    Level 9  
    Posts: 11
    Rate: 1
    Hi, does anyone have experience with this problem.
    The relay has an address assigned to it by the router, but i cannot connect to it after entering the address into the browser. I can change the parameters using UART, but I can't control the relay over wifi.
    Thank you
  • #8 21323485
    GastonL
    Level 4  
    Posts: 7
    Hi,

    I have the same smart switch. Can you tell me how you flashed it? Did you connect an uart/usb device, and if so, how did you wire it?
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  • CB3S pinout and Tuya config mapping

    #9 21324150
    fitor
    Level 9  
    Posts: 11
    Rate: 1
    Hi, standard conection via UART, module CB3S:
    PIN1 - CEN
    PIN8 - Vcc
    PIN9 - GND
    PIN15 - RX
    PIN16 - TX
    Code: text Expand Select all Copy to clipboard
    
{
"rl1_lv":"1",
"on_off_cnt":"10",
"onoff_rst_m":"0",
"led1_pin":"9",
"onoff_clear_t":"6",
"rand_dpid":"42",
"net_trig":"4",
"netled1_lv":"0",
"jv":"100",
"onoff_rst_type":"2",
"total_bt_pin":"6",
"nety_led":"0",
"total_stat":"0",
"reset_t":"5",
"netled1_pin":"8",
"remote_add_dp":"49",
"remote_list_dp":"50",
"net_type":"0",
"inch_dp":"44",
"rf_width":"345",
"module":"CB3S",
"ch_cddpid1":"9",
"remote_io":"26",
"onoff1":"14",
"init_conf":"38",
"led1_lv":"0",
"zero_select":"0",
"onoff_type":"0",
"series_ctrl":"0",
"total_bt_lv":"0",
"cyc_dpid":"43",
"remote_select":"1",
"ch_num":"1",
"rl1_pin":"24",
"netn_led":"0",
"ch_dpid1":"1",
"crc":"16"
}

Device configuration, as extracted from Tuya:
- LED (channel 1) on P9
- Pair/Toggle All Button on P6
- WiFi LED on P8
- TglChannelToggle (channel 1) on P14
- Relay (channel 1) on P24
Device seems to be using CB3S module, which is using BK7231N.
And the Tuya section starts, as usual, at 2023424
    [/code]

    but be careful, out of 4 relays one is not working RF, like in the second post!!
  • #10 21324278
    GastonL
    Level 4  
    Posts: 7
    That's how I connected it, but I did not unsoldier the cb3s. I tried to reset through pin 1 (reset) and pin 3 (cen), but without luck.

    Do I have to unsoldier the cb3s for that? I measured voltage over pin  8 and pin 9 after connecting gnd and 3v, but I measure only a 0.7v, so there is a huge voltage drop.
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  • #11 21324638
    fitor
    Level 9  
    Posts: 11
    Rate: 1
    That's weird. If you have a weak 3V3 power supply on the UART, you can use an external stabilizer.
    But the easiest way is to just connect Rx, Tx and GND and power the relay through its micro USB port.
    You connect the power then the UART, and briefly disconnect and reconnect the USB power when a reset is requested.

  • No AP after flashing CB3S firmware

    #12 21325559
    GastonL
    Level 4  
    Posts: 7
    Your suggestion did help me, but it works differently for me. Steps I did:
    1. wire TX, RX and GND
    2. connect USB/UART to computer
    3. start (windows) BK7231 UART flasher
    4. connect switch to USB for power
    5. shortly wire GND to pin 1 (RST)
    6. disconnect GND

    The results are as below

    note to me: don't swap TX and RX, because that leads to frying a SMD

    Unfortunately, I don't see it come up as an AP neither can I find it on my network when I add wifi credentials. Any flag box I should tick?

    Code: text Expand Select all Copy to clipboard
    
{
   "rl1_lv":"1",
   "on_off_cnt":"10",
   "onoff_rst_m":"0",
   "led1_pin":"9",
   "onoff_clear_t":"6",
   "rand_dpid":"42",
   "net_trig":"4",
   "netled1_lv":"0",
   "jv":"100",
   "onoff_rst_type":"2",
   "total_bt_pin":"6",
   "nety_led":"0",
   "total_stat":"0",
   "reset_t":"5",
   "netled1_pin":"8",
   "remote_add_dp":"49",
   "remote_list_dp":"50",
   "net_type":"0",
   "inch_dp":"44",
   "rf_width":"345",
   "module":"CB3S",
   "ch_cddpid1":"9",
   "remote_io":"26",
   "onoff1":"14",
   "init_conf":"38",
   "led1_lv":"0",
   "zero_select":"0",
   "onoff_type":"0",
   "series_ctrl":"0",
   "total_bt_lv":"0",
   "cyc_dpid":"43",
   "remote_select":"1",
   "ch_num":"1",
   "rl1_pin":"24",
   "netn_led":"0",
   "ch_dpid1":"1",
   "crc":"16"
}



Device configuration, as extracted from Tuya: 
- LED (channel 1) on P9
- Pair/Toggle All Button on P6
- WiFi LED on P8
- TglChannelToggle (channel 1) on P14
- Relay (channel 1) on P24
Device seems to be using CB3S module, which is using BK7231N.
And the Tuya section starts, as usual, at 2023424
  • #13 21325677
    fitor
    Level 9  
    Posts: 11
    Rate: 1
    After flash, choose Read only OBK config, then Change OBK settings and here put wifi SSID and password, then Write only OBK config. For wifi is not necesary to tick any flags.
  • #14 21325907
    GastonL
    Level 4  
    Posts: 7
    That was easy, but I think I fried the AMS 1117 voltage regulator, because the led is on with a fast flicker, there is no WIFI and there is no response from buttons or relay (the AMS started smoking when I had TX-TX and RX-RX connected).

    So that was it I guess, unless I have a AMS somewhere and that's the only defect component.
  • #15 21325924
    fitor
    Level 9  
    Posts: 11
    Rate: 1
    Swapping Tx and Rx will not destroy the chip. You must have switched the polarity of the power supply.
  • #16 21327020
    GastonL
    Level 4  
    Posts: 7
    I agree that it's unlikely to destroy the chip with swapping Tx and Rx. But it's also unlikely to swap polarity using a USB cable to power the switch. I found a AMS1117 on a step down converter and tried to replace it, but that didn't end well. This project stops for me now. It was fun, but I am going to buy a zigbee switch as a replacement now.
  • #17 21327112
    fitor
    Level 9  
    Posts: 11
    Rate: 1
    Didn't you use a 5V power supply instead of 3V3?
  • #18 21327132
    GastonL
    Level 4  
    Posts: 7
    I used the uart on 3v and the USB is the regular way to power the switch (which is 5v of course). Apart from Tx and Rx I don't think anything was connected wrong. But we will never be sure
  • #19 21624939
    Frajar
    Level 1  
    Posts: 1
    Guys, how do I set the device so that after pressing the button, the relay turns off after 1 second?

  • RF learning handled by RFE2740, not CB3S

    #21 21795126
    dlitz
    Level 1  
    Posts: 1
    I have a similar, 4-channel board made by "Huacaoe" instead of "MHCOZY", and I've been working on replacing its firmware with ESPHome. It has the RFE2740DM chip, which has 1 wire connected to the radio transceiver chip (WL520) and 4 wires connected in parallel to each of the buttons. To program it, you apparently hold the button for 3 seconds until a blue LED turns on, and then press the button on the remote. Neither the RFE2740DM nor the WL520 appears to have any connection to the CB3S module except through those 4 button-press GPIOs.

    I haven't gotten out an oscilloscope yet to confirm and I don't have any 433MHz remotes, but based on the way it is wired, I don't think the CB3S MCU has any way to control the RF function; decoding and learning appears to be done entirely by the RFE2740, which is apparently designed to simulate the corresponding button-press when it receives the RF code that it has learned.
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Topic summary

✨ Discussion about flashing and configuring an MHCOZY dry-contact relay module based on the BK7231N/CB3S platform. The original post shares a working OBK/Tuya-style configuration for the TYWRA-RF model, including GPIO mapping for buttons, LED, and relay, plus keywords such as dry contact, 5V USB power, and RF 433 MHz. Follow-up replies focus on preserving or restoring RF learning support after flashing, UART wiring and reset procedure for CB3S, accessing OBK settings after flash, and troubleshooting issues such as missing web interface, Wi‑Fi/AP startup problems, and possible damage to the AMS1117 regulator. Later comments discuss RF receiver integration, remote learning behavior, and whether RF handling is done by the MCU or a separate RF receiver chip.
AI summary based on the discussion. May contain errors.
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FAQ

TL;DR: 15 answers, “remote_io:26” is the clue: this FAQ helps MHCOZY TYWRA-RF owners configure a CB3S BK7231N dry-contact relay after OpenBeken flashing, restore WiFi access, wire UART safely, and understand why 433 MHz RF learning may stay outside MCU control. [#21782497]

Why it matters: A correct pin map and safe flashing method can preserve relay control, avoid regulator damage, and clarify whether RF pairing belongs to OpenBeken or the separate RF circuit.

Option Hardware path What the thread shows Practical result
OpenBeken on BK7231N CB3S WiFi MCU Relay on P24, WiFi LED on P8, buttons on P6/P14 Local WiFi relay control
Original Tuya RF behavior RF receiver/decoder section Tuya dump includes remote_add_dp 49, remote_list_dp 50, remote_io 26 RF learning may depend on RF chip support
Separate RF chip path RFE2740/RFE2740DM plus radio chip RF chip can simulate button GPIOs RF can work independently of CB3S firmware
Zigbee replacement Different module ecosystem One user chose Zigbee after hardware damage Simpler replacement path after failed repair

Key insight: The MHCOZY TYWRA-RF is not just a BK7231N relay. Its 433 MHz learning path may involve an RFE2740-class RF chip, so OpenBeken pin mapping alone does not guarantee RF pairing.

Quick Facts

  • The shared OpenBeken template identifies the device as Tuya MHCOZY TYWRA-RF, chip BK7231N, board CB3S, with dry contact, 5V, USB, and RF 433MHz keywords. [#20606758]
  • Core OpenBeken pins from the first working config are P6 Btn;0, P8 LED_n;0, P14 Btn;0, and P24 Rel;0. [#20606758]
  • Tuya extraction lists LED channel 1 on P9, Pair/Toggle All Button on P6, WiFi LED on P8, channel toggle on P14, and relay on P24. [#21308431]
  • Flashing access used CB3S UART points: PIN1 CEN, PIN8 Vcc, PIN9 GND, PIN15 RX, and PIN16 TX. [#21324150]
  • RF-related Tuya fields include remote_add_dp:49, remote_list_dp:50, remote_io:26, rf_width:345, and remote_select:1 in one later dump. [#21324150]

How do I configure an MHCOZY TYWRA-RF dry contact relay module with a CB3S BK7231N chip after flashing OpenBK7231T/OpenBeken?

Configure it as a Tuya MHCOZY Relay module, model TYWRA-RF, chip BK7231N, board CB3S. Use the shared OpenBeken-style map: P6 button, P8 inverted LED, P14 button, and P24 relay. The original JSON names the device “MHCOZY Relay module (dry contact)” and lists 5V, USB, and RF 433MHz as keywords. This gives WiFi relay control after flashing, but does not prove RF learning works. [#20606758]

What pin configuration should I use for the MHCOZY TYWRA-RF relay module with CB3S, including relay, buttons, and LEDs?

Use P24 for the relay, P8 for the WiFi LED, P6 for the pair or toggle-all button, and P14 for channel toggle. A Tuya extraction also found channel LED on P9. The first shared OpenBeken config used Btn;0 on pins 6 and 14, LED_n;0 on pin 8, and Rel;0 on pin 24. That matches the later Tuya pin summary. [#21308431]

How can I teach or learn a new 433 MHz RF remote on an MHCOZY TYWRA-RF relay after flashing the BK7231N firmware?

Use RF support only if your build and wiring expose the RF receiver to OpenBeken. The later thread points to an RF receiver driver guide and highlights remote_io:"26" from the Tuya extraction. That field is the only concrete RF GPIO clue in this thread. If your board handles RF inside a separate decoder chip, OpenBeken cannot learn the remote through normal relay pins alone. [#21782497]

Why does the MHCOZY TYWRA-RF relay become only WiFi-controlled after flashing, and what happens to the RF remote function?

It becomes WiFi-controlled because flashing replaces Tuya firmware on the CB3S BK7231N module. A user asked why it was “just a wifi controlled relais” after flashing. RF learning may disappear when Tuya datapoints and RF routines are no longer active. In one 4-channel related board, RF decoding appeared separate from CB3S and only simulated button presses. [#20801332]

What is the correct UART wiring for flashing a CB3S module on an MHCOZY TYWRA-RF relay?

Wire the CB3S UART as PIN1 CEN, PIN8 Vcc, PIN9 GND, PIN15 RX, and PIN16 TX. One user described this as the standard CB3S connection. If powering through the relay’s micro USB port, connect only RX, TX, and GND from the adapter. Then reset or power-cycle when the flasher requests boot mode. Keep UART at 3V logic. [#21324150]

How do I flash a BK7231N CB3S relay module using the Windows BK7231 UART flasher?

Flash it through UART, then reset the CB3S into boot mode when prompted. One successful Windows sequence was:
  1. Wire TX, RX, and GND.
  2. Start the Windows BK7231 UART flasher, then power the switch by USB.
  3. Briefly connect GND to PIN1 RST, then disconnect GND. This user warned that incorrect TX/RX handling coincided with SMD damage. [#21325559]

What should I do when a flashed BK7231N relay gets an IP address from the router but the web interface will not open?

Use UART configuration first, because the relay can accept parameters without the web interface. One user reported the router assigned an address, but the browser could not reach the relay. The same user could still change parameters through UART. That makes UART the practical recovery path before reflashing or replacing hardware. [#21311074]

How can I set WiFi SSID and password through UART when the OpenBeken access point does not appear?

Set WiFi credentials by editing the OBK config over UART. The reported sequence is: choose “Read only OBK config,” then “Change OBK settings,” enter SSID and password, and finally “Write only OBK config.” No WiFi flag boxes are needed for this step. This applies when the OpenBeken AP does not appear after flashing. [#21325677]

What does the Tuya extracted configuration mean for pins like rl1_pin, netled1_pin, total_bt_pin, remote_io, and remote_select?

Those fields map Tuya functions to physical pins and RF behavior. rl1_pin:24 means relay 1 uses P24. netled1_pin:8 means the WiFi LED uses P8. total_bt_pin:6 means the pair or toggle-all button uses P6. remote_io:26 marks an RF-related input, while remote_select:1 enables the remote path in that dump. [#21324150]

What is a dry contact relay, and how is it different from a normal powered relay output?

A dry contact relay switches an isolated contact rather than supplying its own output voltage. "Dry contact relay" is a relay output category that opens or closes an electrically isolated contact, letting an external circuit provide the voltage, unlike a powered output that drives load voltage directly. The thread names this device “MHCOZY Relay module (dry contact)” and lists 5V USB power. [#20606758]

What is a CB3S module, and how is it related to the BK7231N chip used in Tuya devices?

CB3S is the WiFi module that carries the BK7231N chip in this relay. "CB3S module" is a Tuya-style WiFi module that contains the BK7231N MCU, exposes pins such as CEN, RX, TX, Vcc, and GND, and runs the firmware replaced by OpenBeken. The Tuya extraction explicitly says module CB3S and BK7231N. [#21308431]

What is an RFE2740 or RFE2740DM RF chip, and how might it handle 433 MHz remote learning independently of the CB3S MCU?

RFE2740DM can act as a separate RF decoder that learns remotes and triggers button GPIOs. "RFE2740DM RF chip" is an RF remote-control decoder IC that connects to a radio receiver and button lines, learning RF codes and simulating button presses without needing CB3S firmware logic. A related 4-channel board used RFE2740DM, WL520, one RF wire, and 4 button wires. [#21795126]

BK7231N vs ESPHome vs Zigbee relay modules — which is better for replacing Tuya firmware in smart relay projects?

Choose BK7231N/OpenBeken when you want to reuse this CB3S WiFi relay. Choose ESPHome only if your target firmware supports the exact hardware path you need. Choose Zigbee when you prefer replacing the module instead of repairing or debugging UART damage. One user stopped after an AMS1117 repair failed and bought a Zigbee switch. [#21327020]

How do I make an OpenBeken relay turn off automatically 1 second after pressing a button?

Set an auto-off action in OpenBeken so the relay turns off 1 second after the button event. The thread only asks this requirement and gives no confirmed command. The concrete target is clear: after pressing the button, the relay must turn off after 1 second. Use the device’s relay channel on P24 when creating the automation. [#21624939]

What safety checks should I do before powering a CB3S relay board by USB while connecting RX, TX, GND, CEN, or RST for flashing?

Check power polarity, logic voltage, ground reference, and reset wiring before applying USB power. Use 3V UART logic, connect GND between adapter and board, and avoid feeding a weak 3V3 rail through the adapter. One safer method used USB for relay power and only RX, TX, and GND for UART. A smoking AMS1117 indicates a serious power fault. [#21324638]
AI summary based on the discussion. May contain errors.
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