What is Inside Spektrum DX7 Receiver

In this document I try to go through my findings and my expectation of board structure and behavior. 

Overview
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 2: Block diagram of the main board of DX7

Things to notice on this board:

1- The first thing I noticed is that the satellite external circuit is identical to the receiver circuit –smaller upper board- inside the DX7 body. To prove that I took the receiver out and solder satellite circuit wires to pins where the receiver board was connected. When I turned on the receiver and the transmitter they could connect to each other.

2- There is three receiver points on this board. One in the middle where the main board connects, one on the left where the satellite socket exists, and another one on the right that is active but cannot be used unless you take the cover and solder your wires there.

I expect this will give extra coverage because you will be able to a receiver board for each dimension and you will cover reliably 3D, so whatever the position of your plane the link will be very reliable.

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 




Output Pins:

Throttle:   Pin 26     P0[6]
Aileron: Pin 4 -    P0[1]
Elevator: Pin 1 -    P0[7]
Rudder: Pin 24 -  P0[0]
Gear: Pin 25 -  P0[2]
Aux 1: Pin 3 -    P0[3]
Aux 2:      Pin 6 –   P2[5] 


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



Orange Receiver

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.