Navio2 PPM Input not working


I have a Navio2 on a Raspberry Pi 3 and most things seem to be working now but I seem to have no RC signals in mission planner. I have a FRSky X4R. PPM signals have been confirmed present using a scope, also confirmed PPM not SBUS.

Any ideas ?

SBUS appears to work, but that’s no good for my RFD868x modems with PPM output :frowning:

sudo emlidtool reports the following.

emlidtool version: 0.8.8
Vendor: Emlid Limited
Product: Navio 2
Issue: Emlid 2017-03-23 5e28de2c424cadfb61a62b88e9c0af98a6d25545
Kernel: 4.4.36-a7765e7-emlid-v7+
Trying to run tests
Testing all sensors
2017-07-27 12:53:27 navio root[6107] INFO mpu9250: Passed
2017-07-27 12:53:27 navio root[6107] INFO ms5611: Passed
2017-07-27 12:53:27 navio root[6107] INFO rcio_status_alive: Passed
2017-07-27 12:53:27 navio root[6107] INFO adc: Passed
2017-07-27 12:53:27 navio root[6107] INFO lsm9ds1: Passed
2017-07-27 12:53:27 navio root[6107] INFO pwm: Passed
emlidtool -h to get more help

Running it without sudo changes the following:

2017-07-27 12:57:53 navio root[6310] ERROR pwm: Failed
– Reason: [Errno 13] Permission denied: ‘/sys/class/pwm/pwmchip0/export’


Could you please post the output of cat /sys/kernel/rcio/rcin/ch2 while your throttle stick is up?


I thought I had an idea to the solution. I gather the Navio auto identifies the PPM/SBUS signal. The FRSky receiver simply doesn’t output any PPM signal until you power the transmitter. No failsafe signal, nothing. So I wondered if I had powered thngs in the wrong order and in the lack of a signal Navio had defaulted to SBUS. So made sure I powered things in the right order and made sure I had a PPM signal then booted the Navio, the result was all zeros while reading /dev/kernel/rcio/rcin/ch0 to ch9 which I guess means no signal. Then without changing anything else I unplugged from the PPM port on the receiver and into the SBUS port and I instantly got readings via /dev/kernel/rcio/rcin/chx.

In the process of making sure I had a PPM signal I hooked up to a scope, and I observed a very odd PPM signal. Normally I would expect a fixed mark and a variable space or vice verse. Channels 3-8 obey this expectation and in my case vary the mark. Channel 2 varys the space and channel 1 does both !! Yet if you measure the rising edge to rising edge times it’s still a valid PPM signal. I wonder if this is confusing Navio ?

I have taken a video and will post later tonight, if I read this post I wouldn’t believe it without proof.


Sorry for the delay, video of the strangeness below.

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