In this document I try to go through my findings and my expectation of board structure and behavior.
My Tiger Trainer plane was completely destroyed in a crash. Even the muffler and the receiver were destroyed. I took this as an opportunity to know what is inside Receiver DX7, and how much is it different than much cheaper receivers such as Orange Receiver.
Boards StructureAfter some investigation I came out with the following outputs:
1- The receiver of DX7 consists of two main boards attached to each other as in figure 1
Figure 1: DX7 Receiver Board
The two boards are:a. The smaller upper board is the actual receiving board and has two antenna attached to it – one of them was detached in my plane crash-.
b. The bottom bigger board is the main board. It takes receiver output and decodes it and sends output signals through output pins to servos.
Figure 3: Main Board, and pin assignment of each receiver.
Figure #3 shows how receivers are connected to CY8C27443 microcontroller.
Datasheet for this microcontroller can be found here
Throttle: Pin 26 P0
Aileron: Pin 4 - P0
Elevator: Pin 1 - P0
Rudder: Pin 24 - P0
Gear: Pin 25 - P0
Aux 1: Pin 3 - P0
Aux 2: Pin 6 – P2
What is can we conclude here is that the microcontroller receive signals from multiple receivers and determine which signal is valid. Then it simply converts serial data to PWM signal for each output. I found interesting topic here discussing details of this point by connecting satellite to Arduino http://www.dogfight.no/2011/01/spectrum-receiver-satellite-to-arduino.html
Although Orange receiver looks much more simple than DX7, but infact we can see many commons here. There is only two ICs the receiver, we should expect three here, but it seems that the second IC performs the decoding function as well, because at the end of the day they are microcontrollers and it is a matter of software updates.
The regulator is another difference, we have only one capacitor and a small regulator which gives an indication of the maximum current they can stand.
Another interested part I noticed is the signals that you receive from channels. Signals are originally send and received in series, then these signals are demultiplexed into their original channels. This means we never get any overlap between any two PWM signals if we measure them from RX output channels. Channels can never overlap.
|Throttle - ALI"green-red"|
|No Signal Overlapping|
If you are interested in more details about signal handling in your firmware and how to protect your quadcopter from losing TX signal while armed please check this link Receiver Handling and Signal Lost Detection Explained