FAQ
TL;DR: If your SM-028_V1.3 switch clicks randomly, add 2 parts—C6 0.1 uF and R1 10 kOhm—because, as one expert noted, "these two cheap components" were omitted. This FAQ helps BL602L20 switch owners stop self-triggering relays and flash OpenBL602 with blflash. [#20904492]
Why it matters: Random relay toggles can shut off loads unexpectedly, create repeated contactor chatter, and waste hours on software debugging when the fault is often on the input hardware.
| Option |
What changed |
Reported result |
Main drawback |
| Add C6 0.1 uF + R1 10 kOhm |
Populate missing input parts |
Original poster reports random switching stops |
Requires SMD soldering |
| Add external 4.7k pull-up + 104 cap |
External pull-up and low-pass filter |
One user reports it works 100% |
Extra wiring, board modification |
| Replace BL602 with ESP-02S + Tasmota |
Swap Wi-Fi module entirely |
One user reports stable operation |
Biggest hardware change |
Use blflash instead of BLDevCube |
Change flashing tool only |
Command-line flashing worked where BLDevCube failed |
Does not itself fix noisy hardware |
Key insight: The thread points to a floating or poorly conditioned switch input, not a relay defect. Firmware can change behavior, but added pull-ups, filtering, or a GND bridge solved the false toggles most directly.
Quick Facts
- The board fix named in the first post is C6 = 0.1 uF and R1 = 10 kOhm on the SM-028_V1.3 BL602L20 relay module. [#20904492]
- The UART wiring used for flashing was TX→RX, RX→TX, GND→GND, 3V3→3V, with BT tied to 3V before connecting the adapter to the PC. [#20904492]
- The working command-line flash example was
blflash-windows-amd64.exe flash OpenBL602_1.17.402.bin --port COM7, while BLDevCube reportedly threw an error on the same hardware. [#20905651]
- One owner bought the module for $2, and other replies argued the omitted input parts would add only about $0.10 with assembly. [#20905651]
- A second hardware workaround used an external 4.7k pull-up with a 104 capacitor as a low-pass filter and was reported to work 100% after removing the underside button. [#21013733]
How do I stop random relay switching on an SM-028_V1.3 smart switch with a BL602L20 chip?
Add the missing input-conditioning parts first: C6 0.1 uF and R1 10 kOhm. The original repair report says this stops the relay from turning on and off randomly on the SM-028_V1.3 with a BL602L20. If your board still misbehaves, later posts show a GND bridge or an external 4.7k pull-up plus 104 capacitor can stabilize the input further.
[#20904492]
Which components need to be added to the SM-028_V1.3 board to fix self-triggering relay clicks, and where exactly do they go?
You need to add C6 0.1 uF and R1 10 kOhm to the unpopulated footprints marked on the board. The first post shows the exact placement area and states these two parts must be soldered in, not removed. A later reply also corrected the unit wording, confirming the capacitor value is 0.1 uF, not 0.1 mF.
[#20905638]
What is the purpose of the C6 0.1 uF capacitor and R1 10 kOhm resistor in this BL602 relay switch circuit?
They condition the switch input so noise does not look like a real press. Together, a 10 kOhm resistor and 0.1 uF capacitor form a simple pull and filter network that biases the GPIO and suppresses brief transients. The thread links their absence to random relay clicks and says installing them removes that behavior in the original ecosystem too.
[#20905651]
How do I flash OpenBL602 firmware onto an SM-028_V1.3 module using blflash from the command line?
Use UART wiring and the
blflash command shown in the thread. 1. Unsolder the SM-028_V1.3 module. 2. Wire TX→RX, RX→TX, GND→GND, 3V3→3V, and BT→3V. 3. Run
blflash-windows-amd64.exe flash OpenBL602_1.17.402.bin --port COM7. The poster flashed OpenBL602 that way after connecting the UART adapter to a PC.
[#20904492]
What is blflash, and how is it used for flashing or reading BL602 devices?
"blflash" is a command-line flashing tool that programs and reads BL602-family devices, using a serial port and explicit actions such as flash or read. In this thread, it was used with
flash OpenBL602_1.17.402.bin --port COM7, and the author later showed that supported commands also allow reading flash contents.
[#20905651]
BLDevCube vs blflash for BL602 modules — which tool works better when flashing SM-028_V1.3 boards?
blflash worked better in this thread for the SM-028_V1.3 board. The author said BLDevCube.exe produced an error and could not be made to work, while the command-line
blflash-windows-amd64.exe successfully flashed OpenBL602 and could also read flash with supported commands. That makes
blflash the proven tool here.
[#20905651]
Why does the relay on some BL602 or BK7231N smart switches change state randomly even when only controlled from the app?
The thread points to unstable input circuitry, not app control alone. Users reported random state changes even when the switch was controlled only from Tuya, and one post noted a device log entry appeared for each false state change. Later fixes that added pull-ups, filtering, or a GND bridge stopped the phantom toggles, which fits a noisy GPIO path.
[#20905075]
How much of the random switching problem is hardware-related versus firmware-related on these eWelink or Tuya-style Wi-Fi switches?
The thread shows both matter, but hardware dominates on these boards. Firmware can change pull-up, pull-down, and debounce behavior, yet several users fixed the problem only after adding C6 and R1, adding a 4.7k plus 104 filter, or bridging to GND. One expert also criticized the PCB for missing protective and filter parts found on better designs.
[#20905059]
What is ToggleChannelOnToggle in OpenBeken, and how can its pull-up or pull-down behavior affect false relay toggles?
"ToggleChannelOnToggle" is an OpenBeken input role that changes a relay channel when a GPIO detects a toggle, with behavior shaped by the input biasing and edge detection. In the thread, an expert suggested separate versions with pull-up, pull-down, and no-pull behavior because the wrong bias can let a floating line generate false relay toggles.
[#20913377]
Why did changing the input role from ToggleChannelOnToggle to Btn stop random state changes for some users?
Changing to
Btn stopped the false toggles because it changed how the firmware interpreted the noisy input. One user said random state changes occurred with
ToggleChannelOnToggle, but not when testing with
Btn. That points to the trigger logic and input bias, not the relay output stage itself, as the source of the problem.
[#20913404]
What does the added bridge to GND actually do in the SM-028_V1.3 fix, and why does it stop the switch from triggering itself?
The GND bridge gives the problematic input path a solid reference, so it no longer floats and self-triggers. A user reported that factory-fitted resistor and capacitor parts still did not stabilize his board, but a bridge to GND did. He also observed frequent chatter, even a dozen times per minute, before that bridge fixed the behavior.
[#20913301]
How can I troubleshoot S1 and S2 inputs on an SM-028_V1.3 board when shorting them to GND does not produce any response?
Check continuity between the S1/S2 connector path and the SM-028 module pads before changing firmware settings. One repair found a fault between the S2 connector and the pad marked R; removing excess solder isolated the bad path, and a bridge from the R pad to the via near S2 restored response to shorting with GND. An added 4k7 pull-up was used as a precaution.
[#20913301]
What is the best external pull-up and low-pass filter fix for BK7231N or BL602 switches that still toggle randomly after removing the onboard button?
Use an external 4.7k pull-up with a 104 capacitor as a low-pass filter. A BK7231N user reported that removing the onboard button did not solve the random toggling, but this external network worked 100%. He also concluded the underside button was not relevant and that the software pull-up did not seem effective on his board.
[#21013733]
How does replacing the BL602 module with an ESP-02S running Tasmota compare with modifying the original board to cure random switching?
Replacing the BL602 with an ESP-02S running Tasmota is a working bypass, not a minimal fix. One user tested that swap and said it worked great without needing the modification discussed in the first post. Compared with adding C6 and R1, the ESP-02S route changes the whole radio module, so it is more invasive but avoids BL602-specific behavior.
[#20913044]
What safety or design weaknesses should I watch for on these very cheap relay boards, such as missing varistors, filter chokes, or input protection parts?
Watch for stripped-down mains input protection and sparse filtering. One expert said this board had only a fuse resistor at the input and lacked a varistor, a second electrolytic capacitor, and the common C0-L2-C1 filter network seen on better Tuya-style designs. The original poster also said the module cost only $2, which matches the aggressive cost cutting noted throughout the thread.
[#20905059]
Comments
Good tutorial. It's a shame that manufacturer tries so hardly to optimize the costs that they don't actually even want to solder those two cheap components. [Read more]
After all, these components cost from $0.10 with assembly, I do not understand this savings. [Read more]
Maybe this should be corrected, as the sentence implies that these components should be removed, not added. [Read more]
By the way, I didn't even know that you can flash BL602 from the command line: .\blflash-windows-amd64.exe flash OpenBL602_1.17.402.bin --port COM7 I've always used BLDevCube.exe, and here's such... [Read more]
So I'm wondering if soldering these components corresponds to flashing in any way? Does soldering alone solve the relay switching problem in the original "ecosystem"? I have several switches under Tuya... [Read more]
But with the original firmware? Firmware can indeed affect the switch state detection to some extent. For instance, it is up to the firmware to determine whether the GPIO used has programmable pull-up... [Read more]
I don't think the ac is the problem. I need to take apart a switch that plays tricks on me sometimes. It's annoying insofar as it works as a pseudo-weather switch for the furnace. And it can turn itself... [Read more]
Look how much the parts are for on jlcpcb. A $0.10 would be 40 cents by now. With all the middlemen along the way it would probably make a buck. Well no two parts cost that much. [Read more]
By the way, this whole board is quite poor in components, even by Chinese standards. Only a fuse resistor protects the input, I don't see a varistor or anything else, and what's more, I don't see a second... [Read more]
Well, I don't know. These switches are rare and completely random in my opinion. It is difficult to talk about the influence of the algorithm here. On the other hand, an entry in the device log appears... [Read more]
0.1 mF or maybe 0.1 uF ? [Read more]
by supported commands - can read flash https://obrazki.elektroda.pl/2602001200_1705076546_thumb.jpg I couldn't flash it using BLDevCube.exe, it throws an error and I couldn't do anything about... [Read more]
this modification is not necessary by replacing the bl602 module with an esp 02s and installing tasmota. I tested it and it works great [Read more]
Just today I came across this thread (after last week's reprogramming of such a switch as in the thread) I took to testing with the swapped firmware on OBK. Unfortunately, I did not get a response to... [Read more]
@adinfo are you using the ToggleChannelOnToggle role here? Maybe it is indeed time to separate it into three versions (versions with pull up, with pull down and without pulls) and let users choose as required.... [Read more]
Yes, I am using ToggleChannelOnToggle - in this case the problem occurred, when I changed for testing, for example, to Btn then the problem with changing the state was not observed. As for the idea with... [Read more]
I also have BK7231N chip and its also chnage the state of S1 so it makes the relay on and off randomly. I removed the on board buttons but the issue is exist. I ll try to add a pull out resistor. [Read more]
https://obrazki.elektroda.pl/8061429500_1711040641_thumb.jpg I made this external pulled up with 4.7k with 104 cap for low pass filter. It works 100%. Pcb down side button removed. My casing has... [Read more]
. https://obrazki.elektroda.pl/8374053800_1740965908_thumb.jpg . Gentlemen, explain to me what gives this bridge that the circuit does not trigger itself? [Read more]