FAQ
TL;DR: Adding a 0.1 µF capacitor + 10 kΩ resistor cuts random BL602 relay toggles by 100 % [Elektroda, pavlenkoblok, post #20905651] “Components cost from $0.10” [Elektroda, gulson, post #20904710]
Why it matters: A two-cent RC network can rescue whole smart-home installs prone to ghost switching.
Quick Facts
• RC fix parts: 0.1 µF/50 V X7R (0603) + 10 kΩ ±1 % (0603) [Elektroda, pavlenkoblok, post #20904492]
• Typical extra BOM cost: ≈ $0.10 per board including automated placement [Elektroda, gulson, post #20904710]
• BL602 UART pins: TX-P3, RX-P4; flash voltage 3.3 V [Elektroda, pavlenkoblok, post #20904492]
• blflash 1.17 writes 512 kB in ≈ 11 s at 2 Mbps [*blflash README*]
• Edge-case: 8 % of users still report bounce until a GND bridge is added [Elektroda, Adinfo, post #20913301]
Why does the relay switch on and off by itself?
The BL602 input pin floats because the factory omitted a pull-up/pulldown and noise-filter network. Mains transients or RF bursts couple into the un-terminated GPIO, triggering false state changes [Elektroda, p.kaczmarek2, post #20905059]
How does the 0.1 µF + 10 kΩ network fix the issue?
The resistor pulls the GPIO to a defined logic level, while the capacitor forms an RC low-pass (≈1 ms) that filters microsecond spikes. Together they eliminate stray toggles [Elektroda, pavlenkoblok, post #20904492]
Do I have to flash new firmware after soldering the RC parts?
No. Soldering alone removes random switching even under stock Tuya firmware [Elektroda, pavlenkoblok, post #20905651] Firmware tweaks help further but are optional.
What if I still get false triggers after adding the RC?
Bridge the switch ground (S2) directly to system GND. Users saw unstable boards stabilise instantly after this jumper [Elektroda, Adinfo, post #20913301]
Can I use software pull-ups instead of the resistor?
Some BK7231 boards ignored internal pulls; external 4.7 kΩ worked where firmware pull-up failed [Elektroda, dhanushkadx, post #21013733]
Is the modification reversible?
Yes. Both components mount between existing pads; desoldering returns the board to stock. No PCB cuts required.
What tools and skills are needed?
- Fine-tip soldering iron, 320 °C. 2. 0603 tweezers. 3. Basic SMD experience. Novices finish in under five minutes per board.
How do I flash BL602 firmware from the command line?
- Wire BL602 TX→USB-UART RX, RX→TX, GND→GND, 3.3 V→3.3 V. 2. Run
blflash-windows-amd64.exe flash OpenBL602_1.17.402.bin --port COMx. 3. Power-cycle device to boot new code [Elektroda, pavlenkoblok, post #20904492]
Can blflash also read the factory image?
Yes. Supported commands include read to dump flash, confirmed by CLI screenshot [Elektroda, pavlenkoblok, post #20905651]
What’s an alternative if I don’t like BL602?
Swap the module for ESP-02S and load Tasmota; users reported stable operation without the RC mod [Elektroda, Epinet, post #20913044]
What happens if I install the capacitor with wrong value?
A 0.1 mF (100 µF) part, as mis-typed once, overloads the GPIO and delays switching by >100 ms—avoid this edge case [Elektroda, gemiel, post #20905638]
Why did the manufacturer skip these cheap parts?
Cost-driven BOM trimming: saving two SMDs may yield ~$0.40 retail increase per unit after mark-ups [Elektroda, zigipl, post #20905013] "Every cent counts in mass production" [Elektroda, p.kaczmarek2, post #20904602]
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]