I am just wondering how I can implement this. Can I just simply use the 3.3v pin and ground pin on DXL shield and connect them to the corresponding 3.3v pin and ground pin on Wemos? If not, I am wondering if the level shifter is used directly on the rx/tx pins or the 5v and ground pins on DXL shield.
Like I said before I don’t use your hardware (DXL Shield & Wemos), and the ROBOTIS e-manual does not carry the complete schematic of the DXL Shield, so I can only provide a best guess from the TTL Comm. Circuit that is provided. @Jonathon may have access to more info than me, so he can check on this too.
According to that TTL circuit, the DXL shield expects 5V on its TX, RX and TX_enable (meaning DIR PIN) and your Wemos most likely provides only 3.3 V on its UART Pins. So a Level Shifter module needs to be used between the DXL Shield and Wemos. Adafruit sells one with some tutorial videos too
Today I thought of another solution for you to consider, but it requires you to ditch that UNO DXL Shield that you already have, and get the MKR DXL SHIELD instead:
First, it is obvious that the headers won’t match with your Wemos D1 R32 as the MKR DXL Shield is designed to sit on top of a MKR ZERO or PORTENTA H7. However, because it is designed to work with a MKR ZERO, the MKR DXL SHIELD is already made to accept UART Inputs at 3.3V and send out DXL packets at TTL 5V levels, so you won’t have to fool with a Level Shifter anymore. I don’t have the needed hardware to test out this idea yet, until a couple of weeks from now. So maybe @Jonathon and @willson can chime in if they think that this approach is feasible or not. I know that Will has a Feather ESP32 but I don’t know if he has time to get into this test or not.