Jeti Lua Apps

A collection of Lua apps for the JETI DS-24 II transmitter, built with a spec-driven workflow (GitHub Spec Kit + Claude Code) in VS Code.

Apps

App	Script	Status	Spec	Based on
Speed Gauge	AG-SpdGa.lua	Released (0.3.0)	001	DFM Speed Announcer by Dave McQueeney (MIT)
Flameout Alarm	AG-FlmOt.lua	Released (0.1.0)	003	Original
Throttle Setup Wizard	AG-TrbSt.lua	Released (0.1.0)	002	Original

Screenshots

Taken on a DS-24 II transmitter.

Speed Gauge: full screen at 121 mph, double size, single size

Flameout Alarm: armed at 60,000 RPM, flameout alarm, disarmed

Throttle Setup Wizard: a guided step, verify passed, the summary. Full guide: Throttle Setup Wizard.

Speed Gauge

Speaks your model's airspeed, warns of stall and overspeed, and shows a speedometer on the main screen. It is based on Dave McQueeney's DFM Speed Announcer, with its callout timing and warnings kept and a gauge, air density correction and a new voice added. It only listens and informs: it never controls the model.

It works with a pitot airspeed sensor such as the JETI MSpeed (anything that reports speed as a telemetry value), or with GPS speed. With GPS the warnings use ground speed, so wind shifts them, and there is no air density correction.

Setup (Applications → Speed Gauge):

• Speed sensor, sensor type (airspeed or GPS) and units (mph, km/h, knots, m/s or ft/s). Every speed setting follows the units, and changing them converts the values.
• A callouts on/off switch, and optionally a continuous callouts switch. Either switch also turns on the warnings; with both off the app is silent, but the gauge and max speed keep working.
• Your model's landing, stall and overspeed speeds, entered as the model's sea-level values. The settings flag an illogical order (stall must be below landing, landing below overspeed).
• Gauge max limit: the top of the dial. Set it to your sensor's top speed to use its whole range (MSpeed: 350 km/h / 215 mph; MSpeed 450 EX: 450 km/h / 280 mph). 0 = auto: overspeed + 15%.

Callouts:

• In a clear voice ("eighty five miles per hour"). The interval runs from the shortest (default 2 s) to the longest time (default 40 s) and gets shorter the more the speed has changed since the last callout, relative to the callout sensitivity (default 10 mph): a steady speed is spoken every 40 s, a 10 mph change after about 20 s.
• Nothing is spoken until the model first passes Callouts start above (default 30 mph). After that callouts stay on for the session, so they continue on approach. No callout is ever spoken below 5 mph.
• Landing speed callouts (on by default): once the model has been above landing speed, slowing below it gives short number-only callouts every shortest time.
• The continuous switch gives number-only callouts every shortest time while above "Callouts start above", with or without the on/off switch.
• Max speed ("max 201 miles per hour") is called about 1 s after each new peak, if it beats the last announced max by at least the callout sensitivity. The max resets at every start-up and with Reset max speed.
• A callout never starts while another is still playing.

Warnings, with stick vibration:

• Stall when the speed drops to the stall setting, but only after the model has first exceeded landing speed (so not on the ground). At most twice per slowdown; it re-arms above landing speed, e.g. after a go-around.
• Overspeed once each time the speed passes the overspeed setting.
• "Airspeed alive" once, when the model first passes "Callouts start above".

The gauge:

• Single size: current speed, max, and a speed bar with the overspeed zone. Double size: a small dial beside the speed and max. Full screen ("Speed Gauge (full screen)"): a large dial with a numbered scale, max in the dial, and rows for stall, overspeed, air density, elevation, temperature and the uncorrected sensor speed.
• The dial's arc shows the current speed (overspeed color past the limit); a yellow marker stays at the session max. The colors can be changed.
• The gauge is drawn for the DS-24 II / DC-24 II. On other DC/DS-24 transmitters the callouts and warnings work, and the window shows a notice instead.

Air density correction (optional, airspeed sensors only). A pitot reads low where the air is thin: about 8% at 5,000 ft on a standard day, more when it's hot. With correction on, the shown and spoken speed, the max and the overspeed check use true airspeed, from your field elevation and the temperature:

• Standard: the standard temperature for that elevation;
• Manual: today's temperature, typed in;
• Sensor: read live from a telemetry temperature, such as the MSpeed's. If the reading is lost or out of range (e.g. a sensor heat-soaked in the sun), it falls back to standard and the gauge shows "SENSOR OUT"; it switches back about 10 s after a good reading returns. A sensor inside a warm fuselage can read higher than the outside air.

Stall, landing and "airspeed alive" keep using the sensor's own speed, because those limits depend on air pressure, not true speed. Leave correction off if your sensor already corrects for air density.

Voice. Speed Gauge speaks in its own voice (Piper "Amy"), in src/Apps/AG-SpdGa/voice/. Those files are licensed CC BY-SA 4.0, not MIT (see CREDITS.md); tools/voice/ regenerates them. The Voice setting switches to the transmitter's own voice, and without the voice files the app uses that automatically.

Install = AG-SpdGa.lua, the AG-SpdGa/ folder, and lib/ag_dens.lua and lib/ag_gauge.lua. Details in spec 001 and the description page.

Flameout Alarm

Watches a turbine's RPM telemetry and sounds an urgent, repeating alarm ("Flameout! Flameout! Flameout!" and a lock tone every 5 seconds, with stick vibration) when the engine spools down after it has been running. A double-size window shows RPM as a segmented bar with an idle marker.

It is advisory only. It never controls the model or the engine. It does not replace the ECU's own failsafe, shutdown or auto-restart logic, or the pilot's own monitoring.

It only works if the turbine's RPM reaches the transmitter as a normal telemetry sensor, i.e. you can pick it in the transmitter's sensor list. What is known per ECU brand (research):

ECU	RPM as a telemetry sensor
JetCat	Yes, through JetCat's, VSpeak's, Digitech's or CB-Electroniks' Jeti converter
Xicoy (V6/V10, also JetsMunt)	Yes, through the Xicoy telemetry adapter (sensor group "Turbine")
KingTech	Yes, through the KingTech telemetry unit or a VSpeak/Digitech converter
Swiwin	Yes, through VSpeak's Swiwin converter. Direct connection: unconfirmed
JetCentral	Unconfirmed: the Telemetry Adapter V2 uses its own Lua app
Enjet Power	Unconfirmed

RPM shown only on a JetiBox screen, or only inside another maker's Lua app, can't be used. Swiwin users: set the receiver's output period to 11-13 ms, not "Auto" (a known Swiwin ECU issue, unrelated to this app).

Setup (Applications → Flameout Alarm). Monitoring stays off until three things are set:

• RPM sensor. If the ECU sends RPM in units other than RPM (e.g. thousands), set Sensor scale so Live RPM reads true engine RPM.
• Idle RPM, typed from the ECU's setup, in thousands (35.0 = 35,000 RPM). Compare it with Live RPM at idle. Too high, and the app arms only on a run-up and a relight won't clear the alarm until you open the throttle. Too low, and the alarm comes later and a restart clears it sooner.
• Cut switch, assigned in its Cut (engine off) position. Moving it to Cut disarms the app silently and is the only way to silence an alarm.

How it decides:

• A turbine start overshoots idle and slowly settles back down, so the app arms on an arming threshold below idle (default 90%) held for the arming time (3 s). The arming threshold must stay above any RPM the engine reaches before it runs on its own; raise the percentage if your engine's start or auto-restart comes close to it.
• RPM below the flameout threshold (default 70% of idle) for the detection delay (1 s) starts the alarm. A throttle chop to idle stays above it.
• During an ECU auto-restart the alarm keeps going; it clears once RPM holds the arming threshold for the arming time.
• If telemetry stops for the telemetry-loss delay (2 s), the app says "Engine telemetry lost" instead of alarming.

A Test alarm switch plays the real alarm on the ground (not while armed). The sounds in src/Apps/AG-FlmOt/ are generated with tools/voice/make_flameout.py and licensed CC BY-SA 4.0, not MIT. Install = AG-FlmOt.lua plus the AG-FlmOt/ folder.

Throttle Setup Wizard

Sets up a turbine's throttle on one two-position safety switch: CUT (Throttle Cut, engine off) or RUN (Throttle Idle, the engine may run). It's simpler and safer than the old habit of clicking the throttle trim down to stop and up to arm; Xicoy's manual warns that digital trims cause an unstable idle and a slow emergency shutdown.

The app guides the transmitter's own setup and then proves it by measuring the throttle signal:

• One recommended setup: Max negative/positive −80/80, Throttle-Idle offset 20%, Throttle-Cut output value −100% (−125% for Xicoy). Tested with KingTech, Swiwin and Xicoy ECUs; should work with most others.
• Guided setup: five steps with the exact values, each with an Open button that jumps to the transmitter menu.
• Verify: an output check, then the four switch/stick positions, including CUT with the stick at full. Each failure names the setting to fix.
• Failsafe: the receiver's throttle output on Out OFF, confirmed by a hand test before the setup counts as complete.
• Optional voice callouts "Turbine off" / "Turbine on", copied to the transmitter's voice folder for its Sounds on Event.

It only reads and instructs. It can't change any setting (constitution I): the pilot makes each change. Use it on the bench with the engine unable to start, remove it from the model once the setup passes, and always re-learn the ECU (Teach RC) afterwards. Full guide, including the setup by hand: Throttle Setup Wizard.

The voice files in src/Apps/AG-TrbSt/ are generated with tools/voice/make_turbine.py and licensed CC BY-SA 4.0, not MIT. Install = AG-TrbSt.lua plus the AG-TrbSt/ folder. Tested on the DS-24 II; older DC/DS transmitters should work but are untested.

Install with JETI Studio

1. In JETI Studio open File → Configuration, and add this line to the list of Lua app sources:

   https://raw.githubusercontent.com/Flazzarious/jeti-lua-apps/main/Apps.json
   

2. Connect the transmitter by USB. The released apps appear in JETI Studio's Lua app list; select one and install it.

Each app installs exactly its released version (its files come from the release tag). Descriptions: Speed Gauge, Flameout Alarm, Throttle Setup Wizard.

For maintainers: after tagging a release, run python tools/publish/make_apps_json.py, commit Apps.json and merge it to main.

Apps here are for telemetry, timers, announcements and displays only. Nothing in this repo may control surfaces, throttle or any flight function. See the constitution: .specify/memory/constitution.md.

Layout

.specify/memory/constitution.md   Rules every spec, plan and task inherits
.luarc.json                       LuaLS config (Lua 5.3, globals are errors)
.vscode/                          Editor settings, recommended extensions
types/jeti.lua                    LuaLS stubs for the Jeti API (v1.5 + notes)
docs/jeti-api-notes.md            The API facts that shape how apps are written
docs/examples/style/HELLO.lua     Style reference app (not deployed)
docs/examples/                    Other reference code, incl. official Jeti demos
docs/vendor/                      Generated full API text (gitignored)
specs/NNN-<feature>/              spec.md, plan.md, tasks.md per feature
src/Apps/                         Mirrors /Apps on the transmitter SD card
  AG-xxxxx.lua                    One script per app
  AG-xxxxx/                       That app's sounds, images, language files
  lib/ag_xxxxx.lua                Shared modules, require("ag_xxxxx")
tools/check.py                    Syntax, forbidden-API, naming, encoding checks
tools/pdf2md.py                   Converts Jeti's API PDF for local reference
tests/test_ag_dens.lua            Optional desktop test for the density module (any Lua 5.3)
tools/probe/PROBE.lua             Dev tool: prints the screen/window sizes in the emulator

Multiple apps, one repo

• Names. Every app script is AG- plus up to 5 letters or digits, so it fits the transmitter's 8.3 limit and stays grouped apart from other authors' apps (DFM-*, RCT-*). The menu name is separate and can be anything. A released filename is never changed, because the transmitter ties each model's settings for an app to its filename.
• Shared code goes in src/Apps/lib/ as ag_xxxxx.lua. One copy is loaded and shared by every app, so modules hold no state of their own.
• Specs are per feature, not per app. A new app and a later change to an existing app each get the next number in specs/.
• Deploying. Copy the app's script, its AG-xxxxx/ folder, and any lib/ modules it uses.

First-time setup

1. VS Code extensions. Open the folder and accept the recommended extensions (Lua by sumneko, EditorConfig). LuaLS reads .luarc.json, so diagnostics also work from the command line and for agents.
2. Spec Kit. This repo already contains the constitution. Commit before initializing, because --force may replace managed files:

   uv tool install specify-cli
   specify init --here --force --integration claude --script ps
   git diff .specify/memory/constitution.md   # restore with git checkout if replaced

3. Full API reference (optional, recommended for agents).

   pip install pypdf
   python tools/pdf2md.py

   This writes docs/vendor/jeti-api.md. It's gitignored because the PDF is JETI's copyrighted document.
4. Lua 5.3 compiler (optional). tools/check.py uses luac5.3/luac from PATH for syntax checks and skips that step with a warning if absent.

Workflow

1. /speckit-specify, /speckit-plan, /speckit-tasks, /speckit-implement for each feature under specs/.
2. Implement in src/Apps/ following the naming rules above.
3. python tools/check.py must pass. LuaLS must show no errors.
4. Run in the JETI Studio DS-24 II emulator: copy the app into %LOCALAPPDATA%\JETI-Studio\Emulator\Apps. For sensors, use LeonAirRC's Emulator Telemetry app. Remember the emulator has os, debug and coroutine; the radio does not.
5. Copy the app to /Apps on the transmitter's SD card (it mounts as USB mass storage). Optionally ship .lc bytecode compiled by the matching firmware/emulator version; .lc files are never committed.
6. First real run on a dedicated test model.

Branching

Branch	From	Merges into	Holds
main			Released versions only. Every commit is a release, tagged
develop	main	main, by pull request only	Finished features waiting for a release
feature/NNN-name	develop	develop, by pull request	One spec's work, e.g. feature/001-speed-gauge

main is updated only by a pull request from develop; GitHub enforces this (a ruleset on main and the PR source is develop check in .github/workflows/main-pr-source.yml). Version bumps and last fixes happen on the feature branch or on develop before that pull request; there are no release or hotfix branches.

• A feature branch uses the same NNN-name as its specs/ folder, and carries that spec from /speckit-specify through /speckit-implement.
• Merge a feature into develop only after tools/check.py passes and the quickstart's emulator scenarios have been run.
• Tag releases on main as <script>-v<version>, e.g. AG-SpdGa-v1.0.0, matching the app's version field. Each app has its own version.
• Never commit directly to main or develop.

Style reference: HELLO.lua

docs/examples/style/HELLO.lua is a small flight timer started by a user-assigned switch. It is not deployed, but check.py and LuaLS still check it. It demonstrates the conventions every app follows: lifecycle, a settings form, pSave/pLoad, a telemetry window, rate-limited loop() and cached display strings.

API coverage

types/jeti.lua follows the JETI DC/DS Lua API v1.5 (December 2019). DS-24 v2 firmware may add functions that aren't in it. Entries marked UNVERIFIED were inferred where the PDF is silent. When a newer API document turns up, update the stubs and docs/jeti-api-notes.md together.

Credits

Speed Gauge is based on DFM Speed Announcer by DFM (Dave McQueeney), github.com/davidmcq137/JetiLuaDFM. Much of its behavior comes from that app, and this rewrite wouldn't exist without it. See CREDITS.md for all credits and license notices, including JETI's demos.

License

MIT. See LICENSE. Anyone may use, modify and share these apps, as long as they keep the copyright and license notice. Apps derived from other people's work also carry those authors' notices, listed in CREDITS.md. Third-party code copied unmodified into docs/examples/ (JETI's demos, DFM Speed Announcer) keeps its own license, stated in each file.

References

• Official apps and demos: https://github.com/JETImodel/Lua-Apps
• Community apps and emulator telemetry: https://github.com/LeonAirRC/Jeti-Lua-Apps
• Best practices: https://www.rc-thoughts.com/2016/09/lua-for-jeti-considerations-and-best-practices/
• Lua 5.3 manual: https://www.lua.org/manual/5.3/