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A new PPM encoder firmware has been released. This applies to APM2.x, APM1.x and the standalone PPM encoder.

Basically, a PPM encoder converts the 8 incoming PWM signals to one PPM signal that is then fed to the main processor. While doing so it detects if a cable from the receiver the the APM gets disconnected or if the receiver stops working.

Changes:

• New interrupt system that handles certain Futaba receivers better (simultaneous changes on groups of R/C channels in fast intervals) (this was already present in v2.3.13)
• Adapted behaviour in case of channel loss: If one channel is lost, it will be set according to the following table. The other channels will continue working.
  
  

  Channel 1	Roll	Set to center (1500 μs)
  Channel 2	Pitch	Set to center (1500 μs)
  Channel 3	Throttle	Set to low (900 μs)
  Channel 4	Yaw	Set to center (1500 μs)
  Channel 5	...	Remain at last value
  Channel 6	...	Remain at last value
  Channel 7	...	Remain at last value
  Channel 8	...	Remain at last value

  
  In ArduCopter and ArduPlane a fail-safe action can be triggered by the throttle low signal.
  This should be carefully configured as explained in the wiki for ArduCopter and ArduPlane.
  
  Also note that this has nothing to do with loosing radio connection between the transmitter and the receiver. The receiver's behaviour when it gets out of range depends on the transmitter/receiver hardware and setup. So make sure to go through all the scenarios before flying

Functionality

APM 2.x LED Status:

• RX - OFF = No input signal detected
• RX - SLOW TOGGLE = Input signal OK
• RX - FAST TOGGLE = Invalid input signal(s) detected
• RX - ON = Input signal(s) lost during flight and fail-safe activated
• TX - OFF= PPM output disabled
• TX - FAST TOGGLE = PPM output enabled
• TX - SLOW TOGGLE = PPM pass-trough mode

APM 1.x LED Status:

Normal mode:

• Error condition (All channels lost or throttle channel lost): blue LED blinks very fast
• Normal behaviour: blue LED blinks according to throttle position

Radio Passthrough mode (for ArduPlane only, using firmware with channel 8 override):

• If throttle position < 1200 μs, status LED is off
• If throttle position > 1200 μs, status LED is on

Normal servo Input (PWM) mode:

• PPM output will not be enabled unless a input signal has been detected and verified
• Verified inputs are lost during operation (lose servo wire or receiver malfunction):
  • The last known value of the lost input channel is kept for ~1 second
  • If the lost input channel is not restored within ~1 second, it will be set to the default fail-safe value (for channel 1-4) or kept at the last value (for channel 5-8)
  • Lost channel signal is restored: Normal channel operation is restored using the valid input signal

PPM pass-through mode mode (signal pin 2&3 shorted):

• PPM output will not be enabled unless a input signal has been detected
• Active signal on input channel 1 has been detected:
  • Any input level changes will be passed directly to the PPM output (PPM pass-trough)
  • If no input level changes are detected withing 250ms:
  • PPM output is enabled and default fail-safe values for all eight channels transmitted
  • Input level change detected again, PPM fail-safe output is terminated and normal PPM pass-through operation is restored

Download

The hex file files are located in the downloads section:

• APM2.x
• APM1.x (or standalone PPM encoder)
• APM1.x (or standalone PPM encoder) (with channel 8 override)

Flashing/Updating

The instructions on how to flash the the PPM encoder firmware can be found in the wiki:

• APM2.x
• APM1.x
• Standalone PPM encoder