Discussions

SUCCESS:
After Diagnostics w/ different verified failing configurations of UBECS, X8R, Pixhawk & RCXEL.
Failure is RCEXEL Ignition Module RPM Connector @ AUX5 on PIxhawk Servo Rail connected.
Passed RCXEL LED on Pixhawk RC9 Passthrough w/ RCXEL RPM connector removed from AUX5.    

Pixhawk Plane 3.7.1 w/ Both RCXEL RPM & RCXEL RX Connector

Fails RCXEL RPM on Aux5
Fails RCXEL LED on/off on RC9_OUT



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Previous Diagnostics:  
Success @ RCXEL switch on X8R Servo Rail w/ X8R SBUS Connection @ Pixhawk removed.  
Fail RCXEL on X8R Servo Rail w/ X8R SBUS plugged in to a Powered Off Pixhawk w/ Power Module Connector removed.  
Pixhawk on X8R Sbus passed all servos, failed RCXEL.  Verify SBUS Wires passed.  

Unplugging the 3DR Power Module from Pixhawk Power Port passed one config @ X8R Servo Rail to switch RCXEL.
Config of 3DR Power Module to PIxhawk has 2 x ground, 1 x 5V & 2 x signal wires.
Disabling Power Module & Attribute BATT/VOLT Params in MP has no result.  

Config is 12V LIPO to 3DR Power Module:
1.  w/ 5V out to Pixhawk Power Port including the total of 5 wires on power port
2.  w/ 12V out to UBEC 5.7V out to PIxhawk, X8R & RCXEL.  
3.  UBEC after the Power Module to measure the current from servos, RCXEL & Navigation LED's.    

Both Switches were tested success with Frsky X8R on Ch 5 w/ SBUS Unplugged
Both Switches were tested fail with Frsky X8R on Ch5 w/ SBUS plugged in at same time.

Previous install of 2.75 before I updated to 3.7 had no fail with RCEXEL Opto Switch RC9_OUT.
Re-installed previous 2.75 and contrary same failure.

3.7 & 2.75 will not switch a New & Old RCEXEL OPTO LED on RC4_OUT, RC5_OUT, RC9_OUT w/ PWM verified in MP & WILL TURN A SERVO IN ALL CONFIGURATIONS.

3.7 will turn a Servo on RC5_OUT w/ PWM verified.
2.75 will turn a Servo on RC4_OUT, RC5_OUT, RC9_OUT w/ PWM verified.

Suggestions?
I set BRD_SBUS_OUT to 1,2,3,4,5,6 & 7 w/ reboot & no result.
I set BRD_SBUS_OUT to 1,2,3,4,5,6,7 without rebooting & no result.

I set on ICE channel to exact PWM Ignition On/Off & no result.


Explanation?

Why will RC4, RC5 & RC9 drive a Servo but not drive a RCEXEL Opto Switch?

Why will X8R drive a RCEXEL Opto Switch but not a Pixhawk drive a RCEXEL with same PWM values on Ch5/RC4, RC5 & RC9?

Hypothesis:
1.  Waveform of PWM or PPM that is incompatible with RCEXEL Opto Switch & is compatible with Servos?
1A.  Does 3.7 have any attributes that would alter the PPM or PWM output so that an RCEXEL Opto switch would fail while success Servos on same RC5_OUT?