Thank you very much for your comment.
- The initial connection was only LED with 1K resistor. The PIN 4 was connected to the LED negative in order to turn it ON/OFF with the digital output pin 4.
- The issue started when I connected Pin 3 and Pin 4 together to ground in order to send SMS to recipient with PIN3 depending on digital output PIN 4 state
- The Pin 4 output started malfunctioning even after I have remove Pin 3, i.e., the LED remained high as the voltage is between 9V and 12V, and no 0V between different states
- The Pin 3 sends SMS when it is connected to either ground or 12V on its own. The LED is almost 30% brightness when Pin3 is connected to its negative leg.
There is definitely a residual voltage that is permanent with or without load applied. Even after I have set the digital output default state to LOW, the LED comes ON immediately I plug the router to Power.
When load is applied whether the digital output is turned on/off it drops to 7V. Without load, the low and high states shows 9V and 12V, respectively. When I connect LED, I can see that the LED brightness increases/decreases at different state but it does not go off at low state.
I have tried to follow the example for factory reset via bootloader method
But I am getting error (incorrect checksum) when I upload (Firmware upgrade URL: 192.168.1.1/index.html) the latest firmware (RUT9_R_00.07.03.4).
What could be the issue with the firmware file?
Thank you for your response in advance.