Servo Out Read PWM

ArduPilot Lua Scripting
1

Hi team

This might be simple, but struggling with reading a servo/relay PWM from mission planner in Lua

im trying to set up a parameter that will listen for the PWM signal on a channel 9, i have 9 set up as RC passthrough

image

and i am sending a signal via the servo/relay section of mission planner
image

but i can’t seem to find the right parameter for reading that output? I’d like to monitor when i toggle it from 1100 to 1900 in Lua, ive tried


local RC9 = SRV_Channels:get_output_pwm(58)


function update()

    gcs:send_text(0, "RC9: " .. tostring(RC9))
  
    return update, 100
  end
  
  return update()

but i just get nil, how should i be trying to read the output pwm on this channel for rc passthru?

im assuming that 58 for the channel is correct as per

image

2

The binding you are using does not use pin number, but rather output function number. Additionally, your script does not continuously update the desired variable. Try this:

local RCIN9_FN = 59

function update()
    local srv_pwm = SRV_Channels:get_output_pwm(RCIN9_FN)
    gcs:send_named_float('RCIN9', srv_pwm)
    return update, 100
  end
  
  return update()

And monitor the script on Mission Planner’s Quick tab by selecting MAV_RCIN9 as one of the values.

Using the servo/relay page will be ineffective for testing. Those are not RC overrides. You will need to supply actual RC input. If you are more clear on your goal, I can help further.

3

Hi Yuri, thanks so much for the reply, as always so quick!

no luck on that either, I have a PWM to analog converter and im giving a high PWM output on a channel that equates to a on or off in DC (led lights for POC) and want to test and monitor the PWM output (im going to set up a timer that once its 1900, after 10 seconds, switch back to 1100, or OFF)

But i think the RC in is the issue, i will need an actual RC IN to monitor it looks like, as there doesn’t seem to be a way of monitoring the PWM out just from the servo/relay page (which is what i was going to use as the control buttons) but i shall use some real RC input instead i think

4

I think this is more like what you want. No RC required. Testable in SITL and should work on any scripting compatible autopilot.

local SCRIPTING_FN = 94
local AUX_FN = 300
local PWM_HIGH = 1900
local PWM_LOW = 1100
local TIMEOUT_MS = 10000
local RUN_INTERVAL_MS = 100

SRV_Channels:set_output_pwm(SCRIPTING_FN, PWM_LOW)

local last_aux_pos = nil
local timeout = 0

function update()
    local aux_pos = rc:get_aux_cached(AUX_FN)
    local now = millis()

    if aux_pos ~= last_aux_pos then
        last_aux_pos = aux_pos

        if aux_pos > 0  and timeout < now then
            SRV_Channels:set_output_pwm(SCRIPTING_FN, PWM_HIGH)
            timeout = now + TIMEOUT_MS
            return update, RUN_INTERVAL_MS
        end

        -- this cancels the timeout when the aux switch goes low
        -- remove this if condition if you always want to let the timeout control the off position
        if aux_pos == 0 then
            timeout = 0
            SRV_Channels:set_output_pwm(SCRIPTING_FN, PWM_LOW)
        end
    end

    if timeout > 0 and timeout < now then
        timeout = 0
        SRV_Channels:set_output_pwm(SCRIPTING_FN, PWM_LOW)
    end

    return update, RUN_INTERVAL_MS
end

return update()

To use it, set a SERVOx_FUNCTION parameter to 94 and control it with the Aux Function page on Mission Planner. It will also trigger on RC input by setting any 2 or 3 position switch RCx_OPTION parameter to 300.

image

Monitor output on the Quick Tab by choosing chXout for the channel you’re using as one of the monitored values (or on the Setup/Servo page):

image

5

Hi Yuri
Thanks so much for this, once again super useful help this will work well!

Out of curiosity, is there a way of listening for the servo/replay page’s toggles? Or will a lua script always need an RCIn to bind a parameter to?

6

It’s an awkward approach and not really worth exploring. You’d have to poll for MAVLink commands, and I don’t think the outcome would be exactly what you’re envisioning.

There are better mechanisms for gathering input…like the one I just showed you.

7

Thanks Yuri, load and clear!

With the example above, i take it that it would be 1 servo per script?

Or would i be able to monitor and control multiple servos for a single script?

8

One script can do a lot more than you probably realize…

1 Like
9

You are once again correct!! Have got what i need working thank you!

As an aesthetic aside, i don’t suppose there’s a way of changing the text on these buttons?
image

similar to how you can on the servo page?

10

Not without a custom build of Mission Planner, I think.