Note: You should follow this guide if your MR3040 router has the original TP-Link firmware

Note: be sure that your MR3040 battery is fully charged

Note: be sure that you downloaded the correct ‘factory‘ file that matches your MR3040 version (V1, V2)

To flash OpenWrt on your MR3040 follow these steps:

1. Download the ‘factory’ OpenWrt image file that matches your MR3040 version (V1, V2)
2. Connect the MR3040 to your PC/Laptop with an Ethernet cable
3. Access the MR3040 OpenWrt web interface by opening a web browser and entering http://192.168.0.1 (the default username/password is admin/admin)
4. In the left menu select ‘System tools->Firmware upgrade’
5. Select the OpenWrt factory image file that you downloaded in step 1.
6. Press the ‘Upgrade’ button
7. Wait 4-5 minutes so that the flash process finish. Monitor the MR3040 LEDs, they should go off and on after a successful firmware flash
8. Access the OpenWrt web interface from your web browser at http://192.168.1.1

Note: The TP-Link firmware web interface is at http://192.168.0.1 the OpenWrt web interface is at http://192.168.1.1

Here is nice tutorial with images written by Gunther Wegner : DslrDashboard and LrTimelapse

Here is a nice video tutorial that explains OpenWrt flashing on TP-Link MR3040

https://www.youtube.com/watch?v=Our-AxmrDJM