Step 2: Connect Control Board to Oscilloscope
By utilizing an oscilloscope, we can determine some of the characteristics of the signal sent between the micro-controller and the transmitter chip.
We connected the lead and ground wire to each of the pins of the transmitter chip until we were able to determine which pin was used for the signal and which was the electrical ground. Adjusting the intensity of the oscilloscope will help to make the image more clearly visible.
Most importantly we were able to determine that the remote control for our helicopter sends a digital as opposed to analog signal.
Also quite important, we were able to measure the voltage level used by the Digital signal to confirm we could read and generate a signal at the same voltage level using our USB-to-Serial cable. If this were not the case we might need to add a simple circuit to step up or down the circuit voltage to match our USB-to-Serial hardware.
In the first photo below the dots along the lower line indicate when packets of data (aka "frames") are being sent. We were able to time the impulses to get an idea of what we need to look at when we moved on to the logic analyzer.
In the second photo by zooming in we can see some of the verticals from the digital signal. Sections of the lines will flicker as the joysticks on the remote control's circuit board are manipulated. This indicates the data in each frame is changing in relation to the directions indicated by each channel.
More specific directions and discussion regards how to use an oscilloscope are beyond the scope of this document.