Battery Watchdog

Description

A ROS package to monitor batteries and shut the system down in the event of critically low voltages. It also includes battery monitor firmware based on the voltage divider principle.

Dependencies

• rosserial : If using the watchdog with its bundled firmware, rosserial is required as it is used for communication

Configuration

calib.config This is used in an attempt to circumvent the imperfections of using a physical voltage divider in order to get a slightly better reading.

The principle of calibration used here is using a linear transformation evaluated using static calibration (see here for some theory and examples).

There are variables in the config file and the linear transformation can be described as:

<voltage_msg> = SCALE * <raw_signal> + BIAS

When you build the project, a shell script will convert these values into a header that is used by the firmware.

watchdog.yaml This config file is a convenient place to store the requisite watchdog rosparams:

• topic: the topic that the watchdog will listen to (alternatively, one could another topic to this)
• sample_size: the watchdog uses a rolling mean to prevent outliers from affecting the script. Sample size is how large of a sample the rolling mean should keep
• warning_thresh: the watchdog issues warnings below this voltage
• warning_offset: the number of messages lower than the threshold that must be received before the watchdog issues a warning
• crit_thresh: the watchdog may power off the system below this voltage
• crit_offset: the number of messages lower than the threshold that must be received before the watchdog will power off the system
• warn_rate: warnings are issued through the terminal. This rate specifies how long the watchdog will wait before issuing another warning (in seconds)

Usage

Building the firmware may be done using Arduino CMake as it comes bundled with rosserial. After building the package with dependencies, you may upload the firmware to the device using:

catkin build --no-deps watchdog --make-args watchdog_firmware_voltage_monitor-upload

See here for more information

After this simply use the provided launch script.

Note on shutdown permissions

By default the user running the script will likely not have permission to shut down the computer itself. One option is running the script as su... but a more elegant solution would be to simply set the user (or all users) to not need a password to use shutdown in the sudoers file.

Ex:

<user> ALL=NOPASSWD: /sbin/shutdown