Help! Simultaneous S-bus and PWM?

[Flying Monkey fab]

Hey,
I have this project in my head where I'd need to drive seven servos and 2 motors. At some point, everything will just need to go to an FC, but in the meantime, can I run the primary channels to an Aura 8 and then pull PWM straight off the receiver for the two channels that don't need any gyro help or does using S-bus shut down PWM?

 

[LitterBug]

That will depend on the receiver. My FrSky R9 RXes will do both PWM and SBUS out at the same time.

 

[tamuct01]

I've done this for some more complicated models that need >8 servos. I connected the first 8 servos to the PWM outputs on the receiver (FrSky S8R) and used a SBUS to PWM module to connect the remaining servos. If memory serves, the remaining servos were for a pan/tilt FPV camera so I could utilize head tracking.

 

[F4vet]

Hi, this is the thread closest to my question about servo Pulse-Width-Modulation (PWM) signals. I know the "standard" PWM signal is a positive pulse 1 to 2 milliseconds in length that repeats at approximately 50 Hz (period = 20 msec). So, for a servo in the center position the oscilloscope would show a signal at ground for 18.5 msec and a 1.5 msec positive pulse between 3.3 and 5 volts. Do any radio systems use an inverted PWM signal? Again, for a servo in center position, that would be a positive signal (3.3 to 5 volts) of 18.5 msec and a negative going pulse of 1.5 msec.

 

[LitterBug]

My question would be "Why?"

 

[F4vet]

As a newbee I have put my planes into the high weeds and trees surrounding our flying field several times. I've found them, but sometimes the search was difficult for my old body. So I am building my own audio locator that will beep if the signal is lost or if I throw a switch on my transmitter. I know such things are already available, but I am an EE and like doing these little projects for myself. I have the breadboard working for positive pulses but wondered if I should change the firmware to detect positive or negative pulses at power-up. If no one uses negative PWM though there is no need for the extra complexity.

 

[Foamforce]

As a newbee I have put my planes into the high weeds and trees surrounding our flying field several times. I've found them, but sometimes the search was difficult for my old body. So I am building my own audio locator that will beep if the signal is lost or if I throw a switch on my transmitter. I know such things are already available, but I am an EE and like doing these little projects for myself. I have the breadboard working for positive pulses but wondered if I should change the firmware to detect positive or negative pulses at power-up. If no one uses negative PWM though there is no need for the extra complexity.

I’ve never seen inverted PWM. There are a lot of things that used to use negative SBUS, so inverter circuits exist (that would also insert PWM) and are also easy to build. Here’s a tutorial.

Creating an SBUS Inverter | IntoFPV Forum

If you want to run SBUS on older flight controllers and your RX only outputs an inverted signal you will need a way to invert that signal again before plugging into the FC. An inverter cable is a simp

intofpv.com

 

[Foamforce]

As a newbee I have put my planes into the high weeds and trees surrounding our flying field several times. I've found them, but sometimes the search was difficult for my old body. So I am building my own audio locator that will beep if the signal is lost or if I throw a switch on my transmitter. I know such things are already available, but I am an EE and like doing these little projects for myself. I have the breadboard working for positive pulses but wondered if I should change the firmware to detect positive or negative pulses at power-up. If no one uses negative PWM though there is no need for the extra complexity.

You said you knew they existed, but maybe didn’t know how cheap they were. Here’s a pair of inverters for $5.

https://a.aliexpress.com/_m0VIIRq

 

[Foamforce]

And here’s a $3 lost model alarm. I have one of these and it works. You just plug it in inline with one of your control surfaces, and if it doesn’t see any change in that control surface in a minute it starts beeping lightly. After another minute it starts shrieking loudly.

Lost Model Alarm

valuehobby.com

 

[Merv]

...Do any radio systems use an inverted PWM signal?...

Back in the 72mhz days, yes definitely some signals were inverted, Airtronics is a brand that comes to mind. In my old Turnigy 9XR Pro with a 4 in 1 multi protocol module, there were options to inverte a signal. If I recall it was under a FrSky system.

Sounds like a great project, maybe add a battery, so if the flight pack get disconnected in the crash, it will still beep.

This sounds like something @Inq would be interested in.