Step 4: Desolder Transmitter from Control Board
After using the oscilloscope to establish a digital signal was being sent between the micro-controller and the transmitter chip, and using the logic analyzer to decode the characteristics and content of its serial protocol, it became clear that the easiest method for us to interface with our radio controlled helicopter via software would be to bypass all other components and communicate with the transmitter chip direction using a USB-to-Serial cable.
Had this not been the case we might have instead used the analog outputs of an Arduino to simulate the voltage levels normally indicated by the potentiometers.
As the transmitter chip was actually a separate circuit board (see photo) and there was enough clearance on the pins connecting the two for us to clip in, we might have been able to record and analyze all of the data being sent to it from the micro-controller without any physically modifications. However we eventually would want to be able to simulate these messages ourselves, which would require powering the transmitter board. If the power switch of the remote control was on then the micro-controller would also be sending data, which would conflict with the data we were generating. If we left the power switch off the transmitter board would also be off, preventing it from sending any data to the helicopter. We considered that we would be able to power the transmitter circuit from the USB-to-Serial cable, however we were not certain that the electricity applied at this point would not also flow back to the micro-controller.
Therefore we decided to desolder the transmitter chip from the remote control entirely as that was the only component we required for certain for our project.