IDLE mode and igniter testing on iPhone
IDLE mode lets you talk to your flight computer over the radio while it sits safely on the ground. With the rocket assembled and lying on its side, you can watch the flight computer’s status live, confirm continuity on each igniter, and fire your ejection charges from a safe distance to ground-test your recovery system — without opening the airframe or running wires out through vent holes. You can also reboot the flight computer remotely, so that once the rocket is standing on the rail it restarts ready for flight. In AltosUI, all of this lives in System menu → Idle Mode.
What IDLE mode is
Every time an Altus Metrum flight computer powers on, it picks one of two modes: idle or flight (pad). In idle mode the flight state machine is disengaged, so no ejection charge will fire unless you command it manually. Idle is also the only mode in which the flight computer listens for radio commands. In pad mode it only transmits, so that telemetry and launch detection get top priority. That is why remote igniter testing and remote reboot only work in idle.
You can tell which mode the board chose by its beeps (or LED flashes). Idle is “di-dit” — Morse I for Idle. Pad is “di-dah-dah-dit” — Morse P for Pad.
Which flight computers this works with
AltosUI reaches the flight computer over the radio, through your TeleBT, so IDLE mode works with the radio-equipped boards:
- TeleMetrum and TeleMini — monitoring, reboot, and igniter testing on their two pyro channels (apogee and main).
- TeleMega — monitoring, reboot, and igniter testing on all six pyro channels.
- TeleGPS — monitoring and reboot only. It has no igniters to test.
Before you start
- Connect your TeleBT v4 to the app. Idle Mode needs a connected receiver; see Pair your TeleBT v4 with AltosUI if you haven’t done that yet.
- Put the TeleBT on the flight computer’s frequency. IDLE mode uses whatever frequency is currently selected in the app (System menu → Select Radio Frequency). The current frequency is shown in MHz in the top info bar. There is no separate frequency setting inside the Idle Mode dialog.
- Know your flight computer’s callsign. More on that below.
- Power the flight computer on in idle mode.
- TeleMetrum and TeleMega choose their mode from the accelerometer: power on with the rocket lying horizontal. Nose-up at power-on means pad mode instead. Listen for “di-dit”.
- TeleMini enters idle only if it hears a command packet within its first five seconds after power-on; otherwise it goes to pad mode. The Altus Metrum manual recommends starting the ground station first, so tap Monitor in the app (below) and then power on the TeleMini.
The callsign
The callsign is the match key on the radio link. Every command the TeleBT sends carries its callsign, and the flight computer ignores any command whose callsign doesn’t match its own. As the AltosDroid manual puts it, this “provides a modest amount of protection against accidentally controlling another person’s flight computer” — which matters when there are a dozen rockets in the prep area.
Enter the callsign configured in your flight computer. Normally that’s your own amateur radio callsign, the one you set when you configured the altimeter, as your local radio regulations require. Callsigns are at most 8 characters. If you’ve never set a callsign on your flight computer, it is still on the factory default N0CALL and will answer regardless of what you enter here.
Entering it
- Open System menu → Idle Mode. The Callsign field is pre-filled with the callsign your TeleBT is currently using.
- Tap the field, type the callsign, and tap Return/Done.
- Tap Monitor. Tapping a button is what saves the callsign and sends it to the TeleBT — nothing contacts the rocket while you’re typing. If you tap a button while still editing, the app asks whether to save the new callsign first.
AltosUI remembers the callsign and sends it to your TeleBT every time it reconnects, so you only need to enter it once.
Don’t confuse this with the callsign prefix on the Setup screen. That field only filters the tracker list during a channel scan and has nothing to do with IDLE mode.
The Idle Mode dialog
| Control | What it does |
|---|---|
| Callsign | The callsign the TeleBT uses to address your flight computer. |
| Monitor / Disconnect | Starts IDLE monitoring. While monitoring is on, the same button reads Disconnect — tap it to stop and return to normal telemetry. |
| Fire Igniters | Opens the igniter test screen. Available once monitoring is running and the flight computer has answered. |
| Reboot | Remotely reboots the flight computer. Available once monitoring is running and the flight computer has answered. |
The usual order is: enter the callsign → Monitor → confirm the flight computer appears → Fire Igniters → when you’re finished, Disconnect, or Reboot once the rocket is on the rail.
Monitoring the flight computer
Tap Monitor and the app shows “Setting up IDLE monitor” while it makes contact. Once the flight computer answers:
- An (idle) indicator appears in the top info bar, along with the flight computer’s callsign, serial number, flight number, and state.
- Battery voltages, GPS (on boards that have it), and igniter continuity refresh every 5 seconds.
- You stay on the Pad tab. Tab switching is locked while IDLE monitoring runs, and any flight previously on screen is cleared.
To stop monitoring, reopen System menu → Idle Mode and tap Disconnect. The app goes back to listening for normal telemetry.
Ground-testing your ejection charges
This is what IDLE mode is really for. Assemble the rocket as if for flight, with the apogee and main charges loaded, lay it on its side, and fire each charge remotely to prove your recovery system separates the way you expect.
The Fire Igniters screen
Tap Fire Igniters in the Idle Mode dialog. You’ll see one row per igniter the flight computer reports — two rows for TeleMetrum and TeleMini, six for TeleMega — each with its live status. Status refreshes every 5 seconds while nothing is armed.
| Row in the app | Flight computer channel |
|---|---|
| Apogee | Drogue / apogee charge |
| Main | Main charge |
| A, B, C, D | TeleMega’s four extra pyro channels |
| Status | What it means |
|---|---|
| ready | Continuity is good: an igniter is connected and the circuit reads closed. |
| open | No continuity: no igniter, a broken connection, or a pyro battery that’s too low. |
| active | The igniter is being fired right now. |
| unknown | The reading falls between open and ready — check your wiring. |
Arm, then fire
- Tap the igniter row you want to test. It’s marked with an asterisk and shown in bold.
- Tap Arm. This opens a 10-second window. The button counts down — “Arm (10)”, “Arm (9)”… — and the armed LED bar lights.
- Tap Fire within those 10 seconds. The selected igniter fires.
After you fire, or if the 10 seconds run out, the screen disarms itself. Every test needs a fresh Arm. A few interlocks keep the sequence deliberate:
- Arm stays disabled until you’ve selected an igniter.
- Fire stays disabled unless an igniter is selected and armed.
- While armed, you can’t change which igniter is selected.
This Arm button is not the same thing as the “armed” status on the Pad tab. On the Pad tab, armed means the flight computer is in Pad mode, ready to detect launch and fire its charges in flight. Here, Arm only opens a 10-second window to fire one selected igniter by hand.
Safety
- Treat every charge as live from the moment the flight computer is powered.
- Keep everyone — including you — clear of the airframe’s separation path before you arm. Sections and nose cones leave with real energy.
- Do the test from a safe distance. Not having to stand next to the rocket is the whole point of doing it over the radio.
Going to the pad: remote reboot
Igniter testing happens at the prep area. Reboot is how you leave IDLE once the rocket is on the rail. Power the flight computer on with the rocket horizontal so it comes up in idle, carry the rocket out and raise it on the rail, then open System menu → Idle Mode and tap Reboot. The flight computer restarts standing vertical, so it comes up in pad mode — no ladder, no screwdriver. If monitoring is on, the app stops it before sending the reboot.
After a reboot in the vertical position, the flight computer is in flight mode and its charges are live. Handle the rocket accordingly. From there, the Pad tab takes over; the launch-day checklist picks up the rest.
If the flight computer doesn’t answer
- “TeleBT not connected” — connect your TeleBT first (System menu → Connect a device).
- “Remote Device Didn’t Respond!” — check three things:
- Is the flight computer on and in idle (“di-dit”)? TeleMetrum and TeleMega must be powered on horizontal.
- Are the TeleBT and the flight computer on the same frequency?
- Does the callsign match the one configured in the flight computer?
- TeleMini never answers — tap Monitor first, then power on the TeleMini. It only listens during its first five seconds.
- An igniter reads “open” — check the igniter, its wiring, and the pyro battery. A low pyro battery also reads as open.
- Reboot and Fire Igniters are greyed out — tap Monitor first; both need a live link to the flight computer.
- You can’t change tabs — that’s expected while IDLE monitoring runs. Tap Disconnect in the Idle Mode dialog.
What stays on the desktop
IDLE mode in AltosUI on iPhone covers monitoring, igniter testing, and remote reboot. Changing altimeter configuration (apogee delay, main deploy height, pyro channel setup) and downloading flight logs still belong to AltosUI desktop. See AltosUI on iPhone: what it is (and what it isn’t) for how the two fit together, and the per-board guides for what each flight computer shows: TeleMetrum, TeleMega, TeleMini, and TeleGPS.