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Archive for August, 2015

Fixed PIN pairing on Bluegiga BLE112 Bluetooth module

31. August 2015 11:30 by Jens Willy Johannsen
Categories: General

I needed to make a Bluetooth LE device that required a more secure pairing with the companion iOS app than just "Click Pair to connect…".

This can easily be implemented in BTLE using a bonded, encrypted connection with man-in-the-middle protection enabled. But the device needs either a display to show the code which should be entered on the iOS device, or a keypad to enter the code shown on the iOS device. If the device has neither, then only the "Just works" method can be used. And this will not prompt for a passkey/PIN code.

"But can't I just hardcode a PIN code in the firmware," I asked Google. And Google said, "No, fixed-passkey authentication is not supported in Bluetooth LE."

But it turns out that there is a solution: pretend the BTLE device has a display and specify a hardcoded passkey in the config.xml file. That way, instead of generating a random key to display to the user, the hardcoded passkey will be generated instead.

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Pixhawk CHDK trigger

18. August 2015 22:02 by Jens Willy Johannsen
Categories: Drones | Projects

pixhawk-chdk

The Pixhawk-CHDK trigger will let you use Pixhawk-based drones (like the IRIS+) with a CHDK compatible camera for aerial photography without using a whole mess of duct taped-together UBECs and LED switches and whatnot.

The Pixhawk-CHDK trigger has three input connections in a 0.1" locking header which is compatible with standard servo lead connectors. Power and ground is taken directly from the flight battery (3S or 4S) and the input signal directly from an auxillary output on the Pixhawk. No need for BEC/UBECs or for powering the servo rail on the Pixhawk.

Output to the camera goes directly to the camera's USB port. (Using a locking 2-pin 0.1" header.)

Configuration

There is also a mini-USB connector for configuring the Pixhawk-CHDK trigger. Configuration is done by connecting the Pixhawk-CHDK trigger to a Mac OS X, Windows or Linux computer and opening a terminal connection (using screen or PuTTY or your terminal application of choice) to the device.

Using a simple command-line interface, a number of intervals (up to 20) can be configured. An interval is simply a definition of an input PWM range and corresponding output pulse length. This will allow the Pixhawk-CHDK to work with all CHDK scripts that use the USB remote control input for control, regardless of how many different commands the script supports.

So if we want the CHDK to receive a 50 ms pulse when the RC signal is between 1800 and 2000 µs, the command would be add 1800,2000,50.

Everything is stored in non-volatile RAM (flash) and the interface currently supports the following commands:

  • help – shows available commands
  • list – shows all defined ranges
  • delete – removes a range
  • add – adds a range
  • show – shows all or a specific settings parameter
  • set – modifies a settings parameter
  • pulse – sends an output pulse of the specified length for testing CHDK scripts
  • isp – enters ISP mode for flashing new firmware

Want one?

Everything is open source and open hardware; all schematics, board files and firmware will be made available shortly along with BOM and assembly instructions.

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