DevMon running in the Ethos X20 simulator.

DevMon widget

DevMon is a graphical mixer monitor, designed to facilitate the development and testing of an Ethos setup. It displays a virtual representation of your model which responds to the controls in real time. It can run on a transmitter, or the simulator.

DevMon also displays the numerical mixer values, logical switch states, and timers.

All this means you can quickly check the behaviour of your mixer design at all stages of development. Once you're happy with the design, it can be married to the real model with the minimum of further work (final adjustments for linkages will be made in the Outputs menu).

DevMon has been tested on the X20, X18 and X10. It also runs in the Ethos X20 and X10 simulators, so you can develop a setup entirely on your computer. And if you don't have a transmitter yet, you can familiarise with Ethos programming before purchase.

Key features of DevMon


On first use, DevMon automatically assigns the lower 9 channels to 'virtual' control surfaces, using the channel names as clues to their function. The assignments can be changed in the Widget Configuration menu, and the display automatically adapts to the changed layout.

Example tasks

Some things you can do with DevMon:

Model-free design method (well almost!)

The following is a design method which minimises the need to assemble the model. It applies to both tx and sim based editing.

  1. Create a new setup on the sim or transmitter.
  2. If your setup has dual ailerons, flaps or Vtail, rename those outputs in the form 'RtAil', 'LeftAil, 'RtFlap' as this tells DevMon which side to display each surface. There's no rigid syntax, DevMon can usually make a good guess.
  3. Assign the DevMon widget to a full screen view.
  4. On first use, DevMon will guess the control surface for each channel. Check these are correct. Fix if necessary in the Widget Configuration menu.
  5. Check that the surfaces move in the right direction as you move the sticks. Reverse surfaces if necessary in the Widget Configuration menu (this only affects the movement on screen, it does not alter the model definition).
  6. Now build up your design, adding mixers step by step. Use DevMon to check each addition.
  7. Assemble the model, and finalise servo direction, centre and limits for each channel, using the Outputs menu.
  8. Fine tune input weights, to achieve the correct control surface travel.

Steps 1 to 6 can be accomplished using DevMon - the model is only needed for steps 7 and 8.


DevMon can run either in your X20 transmitter, or in the Ethos simulator. It also works with the X18 and X10, though text may overflow into adjacent panels (this is due to the relatively larger fonts).

  1. Download the script, and save as 'devmon.lua'.
  2. Copy the file as follows:
    • For transmitter: copy to "\scripts" folder on SD card.
    • For Ethos simulator: copy to folder "C:\Program Files (x86)\FrSky\Ethos\X20\scripts" or similar (the exact path may differ on your system). Transmitter actions can be simulated via these shortcut keys.
  3. Create a 'full screen' layout and select the DevMon widget

DevMon 1.4


Transmitter running Ethos, or Ethos simulator
Ethos v 1.4.0 or later (not tested with earlier versions)


devmon.lua (right click and 'Save link as')


Feedback and queries are always welcome - you can contact me from here.