Remember when I was talking about Protocols and the RSS? Well then this will fit right in.
The Analysis: First we have to find all of the I/O in the Gables G-1981 ATC Transponder Panel and find out what they do. First a little background about ATC Transponders:
"is an electronic device that produces a response when it receives a radio-frequency interrogation. Aircraft have transponders to assist in identifying them on radar. Air traffic control towers use the term squawk when they are assigning an aircraft a transponder code, Squawk 7421"
The code is 4 octal numbers. What's octal? Octal is 0 through 7 coded in 3 bits. So 4 octal numbers = 12 bits.
| Function Switch | Positions | Bits |
|---|---|---|
| Function Switch | 4 | 2 |
| Mode Switch | 4 | 2 |
| ATC TR Switch | 2 | 1 |
| Test / Monitor Switch | 3 | 2 |
| ALT Switch | 3 | 3 |
| Code Switches x 4 | 7 x 4 | 12 |
| IDENT | 2 | 1 |
| Panel Lamps | ||
| Dial Lamps | ||
| Monitor Lamp | ||
| Total Bits Needed: | 23 | |
So now we have all of the outputs.
The inputs are much easier you only have: panel lamps, dial lamps, and the Monitor lamp.
The Plan: is really two parts:
Plan what embedded microprocessor to use. And for a change its really a no brainier. I am going to use a Arduino Mega as it has lots of I/O.
A) Design both sides of the protocol.
The output of the Arduino is 23 packed bits, +1 bit for packing giving me 3 packed Bytes plus house keeping of 1 Start Byte, plus one Radio_ID Byte, making the total of 5 Bytes.
A.1) Write to Arduino to the IOP.
A.2) Write from the IOP to the Arduino
A.3) Write the Linux driver in the IOP
A.4) Write the Linux IOP to the Arduino.
B) Test in stages.
B.1) Use the serial monitor to see outbound traffic from the Arduino
B.2) All of the ATC head inputs must come from the Interface Card as it requires 5vdc for the various lamps.
B.3) Make sure that the ATC Transponder does not need to be hacked. If so note it and fix it.
B.4) Now I can build the I/O Cable.
B.5) Install into the RSS and verify that every switch is functioning properly.
C) Go Flying!
Keep Tuned In More To Come
Cris H~
BTW I wish to thank the folks a Gables Engineering for there great support and documentation of the various control heads that we are using.
