FS-i6 trainer socket → Nano#

Connect the transmitter directly to USB through your classic ATmega328P Nano. The receiver is not used. This guide pairs a socket illustration with a PPM diagnostic sketch and the existing RCForge bridge.

Using another Arduino? The same PPM-to-USB-serial approach can work with board-specific firmware. See other Arduino boards before copying this Nano wiring.

Enlarge diagram ↗

What has been tested#

Trainer PPM reception has been demonstrated on one user setup. Receiver connections are still to be tested. User-supplied Serial Monitor output showed six decoded channels, changing stick values, and a reported CH6 RUN position. This establishes basic trainer-to-Nano reception, not every control, electrical level, or an end-to-end flight test.

The bridge subsequently emitted RCF1 packets with status 0. Accepted flight input, calibration and signal-loss recovery still need confirmation. See test status for the receiver limitation.

1. Identify the plug before wiring#

The drawing shows the socket viewed from outside the transmitter, with the antenna above it, as in your photo. The labeled photograph from a working FS-i6 adapter project identifies the upper-left contact as PPM OUT and the outer metal ring as GND, with the rectangular key opening at the top. Leave the other three contacts unused. Ground is the metal shell, not another hole. This is a builder-reported reference, not a manufacturer-certified pinout; verify your radio and cable. Looking at a plug's solder side can reverse left and right.

Use an FS-i6-compatible trainer PPM-output breakout with documented contacts. You need only PPM OUT and GND. Do not insert loose jumper wires into the socket, infer a pin from wire color, or assume a physically matching S-video/PS/2 cable has the correct wiring. A firmware-update USB cable is not a PPM-to-USB joystick adapter.

The manufacturer sources checked do not establish the numbered contacts for your exact cable; the drawing now includes the separate builder reference above. A separate builder reports a working FS-i6 trainer PPM adapter, but that project uses a Leonardo and its D4 input; our classic Nano sketch uses D2. Its wiring is not proof of your cable's contact assignment.

If the cable documentation does not specify electrical levels, have PPM OUT checked with an oscilloscope and suitable probes. This circuit expects LOW near 0 V and HIGH at 3.3–5 V, with no negative voltage. An ordinary multimeter cannot verify pulse peaks. The resistors below do not convert an unsuitable voltage.

2. Make the two-wire connection#

Unplug USB and turn off the transmitter before wiring. Disconnect the receiver and all its wires from the Nano.

Power the Nano from its USB data cable. Power the transmitter from its own batteries. There is no 5 V connection between them. Use the Nano pin labels: D2 is not D0/RX, D1/TX or RST. Compare the official Nano pinout.

The transmitter can still emit RF while a trainer cable is attached. Keep real aircraft/ESCs powered off during simulator setup.

3. Upload the diagnostic sketch#

Open ppm_monitor.ino inside its ppm_monitor folder. This sketch only reads D2; it does not drive the radio or decode unknown serial protocols.

1. In Arduino IDE choose Arduino AVR Boards → Arduino Nano and the appropriate ATmega328P processor/bootloader. Use Old Bootloader only if your board needs it.
2. Select the current USB serial port. Upload with the transmitter wires disconnected; reconnect only after unplugging USB.
3. Open Serial Monitor at 115200 baud. With no signal it should keep printing NO SIGNAL; the USB port should remain present.
4. Turn on the transmitter using a dedicated simulator model. Follow its firmware's student/PPM-output setting if required. Trainer input mode and receiver PPM settings are not equivalent to trainer output.
5. Move one stick at a time, then each knob/switch. Identify the changing channel rather than assuming an assignment. Student mode can bypass normal model settings.

Example output only, not captured from your hardware:

PPM | channels=6 | CH1=1500 | CH2=1500 | CH3=1000 | CH4=1500 | CH5=1500 | CH6=1900 | bridge guard: RUN

Intervals are measured between rising edges, with a sync gap over 3000 μs and channel intervals of 800–2200 μs. Values commonly fall near 1000–2000 μs. The monitor prints four times a second. Its built-in LED indicates a fresh valid diagnostic frame, even if CH6 is STOP; this differs from the guarded bridge LED.

4. Upload the RCForge bridge#

The monitor prints readable diagnostics; RCForge cannot use those lines as flight input. Once six-channel PPM is verified, open rcforge_bridge.ino in its matching folder and upload it instead. No extra Arduino libraries are required.

Leave these settings enabled:

#define RCF_INPUT_MODE 1
#define RCF_GUARD_CHANNEL 6

Set the physical CH6 control above 1700 μs for RUN, below it for STOP. If student mode provides no usable CH6 control, read the narrowly scoped wired-trainer exception before changing the guard. Do not apply that exception to a wireless receiver.

1. Serial Monitor at 115200 should show RCF1 packets. Status 1 means six fresh channels and guard RUN; 0 means STOP or invalid input.
2. Close Serial Monitor. Open RCForge in desktop Chrome on localhost or HTTPS.
3. Choose Controllers → RC transmitter → Connect Arduino, select the Nano, then map and calibrate the four flight controls.
4. With throttle low, test STOP and transmitter power-off. Input must become unavailable and flight must pause. Restoring the signal must not resume flight automatically.

If RCForge says “Input stopped”#

The USB port has opened, but the bridge is not reporting accepted live input. In RCF1,502,0,PPM,6,..., the third field is the validity flag. When it is 0, the six values that follow are substituted inactive values, not raw stick readings. You cannot use the displayed CH6 fallback of 1000 to conclude the physical switch is low.

1. Put the control that produced RUN in the diagnostic into that same position, with throttle low.
2. Disconnect RCForge before opening Serial Monitor at 115200. Look for RCF1,number,1,PPM,6,....
3. If the status stays 0, temporarily upload the diagnostic again to distinguish missing/malformed pulses from CH6 STOP. Do not change pins or disable the guard to hide an unknown signal problem.
4. Upload the bridge again after diagnosis, close Serial Monitor, reconnect and calibrate. Reconnecting does not automatically resume a flight.

Failed to open serial port happens earlier: close Serial Monitor/other serial clients, reconnect USB and select the current port in desktop Chrome. It is not a CH6 rejection.

Sources and verification#

• FlySky FAQ, simulator connections: PPM simulator adapter options.
• FS-i6 manual, student mode: transmitter settings; not a verified cable pinout.
• Arduino Nano pinout: board pin names.

The SVG is an original schematic illustration. Both sketches are compile-checked for classic Uno, Nano and Nano Old Bootloader by bash scripts/check-arduino.sh. Compilation does not verify your cable pinout, electrical levels or physical hardware behavior. The diagnostic sketch is not a calibrated measuring instrument.