433 MHz RF Relay: Why ON/OFF Doesn't Work - and How to Fix It

Problem

According to the documentation, the relay supports interlock (latched) mode, where:

• the first button turns the relay ON
• the second button turns the relay OFF

However, when attempting to program this mode, the learning process fails. Both buttons behave identically, making correct ON/OFF operation impossible.

Toggle mode works as expected, which often leads to the assumption that the relay or firmware is defective.

Observation

Practical testing shows that:

• the receiver correctly supports interlock mode
• the learning procedure is performed correctly
• both buttons on the remote trigger the same action

This indicates that the issue is not related to receiver memory, firmware, or learning sequence.

Root Cause

Opening the remote control reveals the actual cause.

Both buttons on the PCB are routed to the same microcontroller input. The board uses 0 Ω resistors as configuration jumpers, and in the factory configuration both buttons share a single signal path.

As a result:

• both buttons generate the same RF code
• the receiver cannot distinguish between ON and OFF commands

This is a hardware configuration choice, not a firmware limitation.

Fix

The PCB is a universal design that supports multiple routing options.

By relocating a 0 Ω jumper to an alternative position:

• each button is connected to a separate MCU input
• the remote starts generating two distinct RF codes

No firmware changes are required.

No modification of the receiver is necessary.

Result

After the jumper reconfiguration:

• interlock (latched) mode programs successfully
• one button reliably turns the relay ON
• the second button reliably turns the relay OFF
• a single remote works exactly as described in the documentation

Notes

This case highlights a common pattern in low-cost electronics:

• documentation often describes an ideal configuration
• shipped hardware may use cost-saving shortcuts
• many "firmware bugs" are actually PCB routing decisions

In this case, the receiver worked correctly from the start. The limitation was entirely inside the remote control hardware.