dmpriso / joystick_to_ppm

Joystick to PPM converter using Raspberry Pi and Arduino

Joystick to PPM Adapter using Raspberry PI and Arduino

General

This project is still work in progress, I've done that for a FPV Groundstation. It does not have an UI (perhaps someone wants to write one?), instead, channel mappings are done using a configuration file.

Hardware

All you need is a Raspberry Pi, a Linux compatible Joystick and an Arduino board. Plug the Joystick into Raspberry. Connect the Raspberry to the Arduino via USB. The Raspberry will use the following devices (this is currently hard-coded)

Joystick:

/dev/input/js0

Serial:

/dev/ttyUSB0

The Arduino will output a 12-Channel 22.5ms PPM signal on Pin 10. Arduino code is based on previous work: https://github.com/ckalpha/Generate-PPM-Signal/

Configuration

At the moment, configuration is done via a settings file. Path of the settings file is /usr/local/etc/joystick/mappings.ini TODO: make that customizable via parameter

You can map axis and buttons to output channels, and define special actions for buttons. Configuration is an INI file. Ini parsing is based on previous work: https://github.com/atomicptr/libini

How do I find axis and button IDs?

Install jstest on your raspberry and run

jstest /dev/input/js0

I strongly recommend you to perform a joystick calibration and save the joystick configuration on your system. See the following article for instructions: http://aegidian.org/bb/viewtopic.php?t=12217#p178651

Axis mapping

An axis mapping entry consists of the following elements:

[axis2]             # "2" is the axis identifier, as seen in jstest
ppm_channel_id=0    # "0" is the PPM channel ID, zero-based
weight=100          # 100% weighting. For reversing, just put a negative value here
expo=30             # 30% expo
offset=10           # 10% offset = subtrim

You may target the same PPM channel ID from multiple axes in order to achieve mixing.

Button action

Button actions are defined as follows:

# flightmode: manual
[action_button9]    # "9" is the button identifier, from jstest
ppm_channel_id=4    # target PPM channel ID, zero-based
value=-67           # value to be set when button is pressed. Range from -100 to +100%

# Below is a release button action. One can also use it to init default PPM values.
# This one is intended to set the initial flightmode to "manual"
[action_releasebutton9]
ppm_channel_id=4
value=-67

Trims and subtrims

Buttons can be set for trims and subtrims. Trim applies to a stick input, so expo and rate are also applied to the trim. Subtrims are applied to PPM output.

[trim_button15]		# Apply trim when button 15 is pressed
axis_id=1			# Target axis ID 
step=1				# Trim step, in percent

[subtrim_button20]	# This is a subtrim when button 20 is pressed
ppm_channel_id=1	# Target PPM channel ID, zero-based
step=1

Trims are automatically saved and restored. The path of the file generated is: /usr/local/etc/joystick/user_trims.ini TODO: make that customizable via parameter

Buttonization of axes

Some joysticks do report their coolie hat as axis, not as buttons. However the coolie hat might be useful for trimming. You can use an axis to trigger button actions as follows:

[buttonize_axis7]	# Axis ID of the coolie hat X or Y axis
low_button_id=34	# Virtual button ID to be triggered when axis is low (left)
high_button_id=35	# Virtual button ID to be triggered when axis is high (right)

Sample configuration

I've added a mapping.ini to the source repo which I wrote for the Saitek X-52 Pro Joystick.

Building and installing

Building

Install CMake and ninja Clone the repo Create a build output directory (outside the repo!) Inside build dir, run the following:

cmake path_to_source_dir -G Ninja
ninja

Testing

Create a /usr/local/etc/joystick/mappings.ini and set it up Simply run ./joystick_ppm_converter for testing

Installing

In order to let the tool automatically run when the raspberry starts up, copy the executable tool to /usr/local/bin/ Then, edit /etc/rc.local and add the following line near the end, but before the exit command:

/usr/local/bin/joystick_ppm_converter >joystick.log &

Restart your raspberry to verify

TODOs

The project is still at a very early alpha-stage. Most important items to do are:

• Improve file parsing so invalid numbers etc. are catched and proper error messages are emitted
• Make the INI paths customizable via command parameters
• Create a GUI for editing the configuration
• Integrate the GUI and allow for live updating of configuration

joystick_to_ppm's Issues

Something's not working here.

Houston we've got a problem. I got an error message when trying to start this one.

stream-UCO4GBqR_0.mp4