Radio Stack
Build log for the Cessna 172SP radio stacks — two GNS 430s, an audio panel and a transponder for the six-pack, and the G1000's COM/NAV heads, GMA 350 and GTX 345.
Overview
The radio stack sits in the centre of the instrument panel, and it differs between the two avionics modules. The six-pack module carries the radios X-Plane 12's default Skyhawk has: two Garmin GNS 430 COM/NAV/GPS units, an audio panel and a transponder. The G1000 module tunes its radios on the PFD and MFD, so its stack is a set of standalone heads kept for the feel of a real knob.
Each unit is its own ESP32, so a unit can be built, tested and replaced on its own. In the app they're part of the Cessna 172 (six-pack) and Cessna 172 G1000 Blueprints.
Six-Pack Radio Stack
| Unit | Function |
|---|---|
| GNS 430 #1 | COM1 / NAV1 and GPS |
| GNS 430 #2 | COM2 / NAV2 and GPS |
| Audio panel | Transmit and monitor selection, marker beacon lights |
| Transponder | Squawk code entry, mode, reply light |
GNS 430
Both GNS 430s are wired the same way, so one design is built twice. The GNS screen stays an X-Plane pop-out window on a small monitor behind the bezel; the bezel carries everything you touch.
| Control | Part | X-Plane 12 |
|---|---|---|
| COM/VLOC knob, outer / inner | Concentric encoder | sim/GPS/g430n1_coarse_up / _down, fine_up / _down |
| COM/VLOC knob push | Push button | sim/GPS/g430n1_nav_com_tog |
| COM and VLOC flip-flop | Push buttons | sim/GPS/g430n1_com_ff, nav_ff |
| C/VOL and V/VOL | Potentiometers with push | sim/cockpit2/radios/actuators/audio_volume_com1, audio_volume_nav1; push g430n1_cvol, vvol |
| FMS knob, outer / inner, push | Concentric encoder, push button | sim/GPS/g430n1_chapter_up / _dn, page_up / _dn, cursor |
| RNG | Rocker | sim/GPS/g430n1_zoom_in, zoom_out |
| D→, MENU, CLR, ENT | Push buttons | sim/GPS/g430n1_direct, menu, clr, ent |
| CDI, OBS, MSG, FPL, PROC, VNAV | Push buttons | sim/GPS/g430n1_cdi, obs, msg, fpl, proc, vnav |
The second unit uses g430n2_*, COM2 and NAV2; only the first has a VNAV key in the Skyhawk. Active and standby COM and NAV frequencies show on four 6-digit seven-segment windows on one MAX7219 chain.
The 18 keys sit on two MCP23017 I²C expanders (GPIO 21 SDA, 22 SCL); the encoders and the two volume potentiometers (ADC1, GPIO 34 and 35) use the ESP32's own pins.
Audio Panel
| Key | Command | Lamp |
|---|---|---|
| COM1 MIC | sim/audio_panel/transmit_audio_com1 | lit while audio_com_selection is 6 |
| COM2 MIC | sim/audio_panel/transmit_audio_com2 | lit while audio_com_selection is 7 |
| COM1, COM2, NAV1, NAV2, ADF | sim/audio_panel/monitor_audio_* | audio_selection_com1 … audio_selection_adf1 |
| DME | sim/audio_panel/monitor_audio_dme | audio_dme_enabled |
| MKR | sim/annunciator/marker_beacon_mute_or_off | audio_marker_enabled |
| SENS | sim/annunciator/marker_beacon_sens_toggle | — |
The outer, middle and inner marker lights follow sim/cockpit2/radios/indicators/outer_marker_lit, middle_marker_lit and inner_marker_lit. The keys are on an MCP23017; the 12 lamps are LEDs on the ESP32's own pins.
Transponder
Keys 0–7, CLR, IDENT, OFF, STBY, ON and ALT send sim/transponder/transponder_digit_0 … _7, transponder_CLR, transponder_ident, transponder_off, transponder_standby, transponder_on and transponder_alt. A 4-digit window shows the squawk (transponder_code, padded as 0743), a second one the mode (OFF, STBY, ON, ALT), and an LED the reply light.
G1000 Radio Stack
In the G1000 module the stack sits in the lower centre: the GMA 350 audio panel at the top, the COM1/NAV1 and COM2/NAV2 heads, and the GTX 345 transponder at the bottom. In a G1000-equipped aircraft the heads are largely redundant with the G1000's own COM/NAV tuning, but they are retained for their physical presence and the tactile feel of tuning a radio with a real knob. They tune the same radios the PFD does.
| Unit | Function |
|---|---|
| Garmin GMA 350 | Audio panel — transmit and monitor selection |
| COM1/NAV1 | Primary comm and nav radio head |
| COM2/NAV2 | Secondary comm and nav radio head |
| GTX 345 | Mode S transponder with ADS-B |
COM/NAV Heads
Both heads are wired alike, each on its own ESP32. A COM and a NAV concentric knob tune the standby frequency (sim/radios/stby_com1_coarse_up / _down, stby_com1_fine_up / _down, and the NAV and second-radio siblings), and a flip-flop button swaps it (sim/radios/com1_standy_flip, nav1_standy_flip). Active and standby COM and NAV frequencies show on four 6-digit seven-segment windows on one MAX7219 chain, as on the six-pack's GNS 430s.
GMA 350
The same keys and lamps as the six-pack's audio panel (COM1 MIC, COM2 MIC, COM1, COM2, NAV1, NAV2, ADF, DME), with MKR as a monitor key: sim/audio_panel/monitor_audio_mkr, lit from audio_marker_enabled. The G1000 shows the marker beacons on the PFD, so the GMA 350 has no marker lights.
GTX 345
Like the six-pack's transponder, with VFR in place of OFF: keys 0–7, CLR, IDENT, VFR, STBY, ON and ALT (sim/transponder/transponder_vfr for VFR). The mode window also shows GND when X-Plane puts the transponder in ground mode.
Status
Both stacks: wiring and X-Plane mapping defined (Cessna 172 six-pack and G1000 Blueprints). Physical build not started.