Servo-Voltage POWR.VServo not logged [solved]

[Quaxwilly (Willy Zehnder)]

After severe problems with servo-voltage I had a look in the logfiles. There I have seen, that the values of POWR.VServo are all filled with NaN.
That’s the case on both of my FCs: MATEKSYS F405 WING and MATEKSYS H743-WING

I found two discussions in the forum

Cube orange - servovoltage is not detected

I just noticed that the servovoltage of the cube orange does not seem to be detected. I have connected a parachute to the servo output and supply the pin header externally with 5V. The servovoltage is 0V. Up to now I have always used the Piixhawk 3 pro, and everything was ok. Can anyone confirm that there is a problem with the cube orange or have I forgotten a setting? [2020-03-18_220119]

POWR: System power information

Does “Log”-> “POWR”-> “Vcc: Flight board voltage” measure the voltage from the battery to the flight controller via the power module? And what voltage does “VServo” measure?

but both does not explain how to solve my problem.

Is there an ADC-Input missing on that boards or do I have to configure the log of that value?

I found an #if HAL_HAVE_SERVO_INPUT in the code, but I have no idea, how/if to set/define it correctly or in which cases the logging of POWR.VServo is possible or not.

Can anybody help me to solve my problem and explain the background?

[Jai.GAY]

@Quaxwilly

Can anybody help me to solve my problem and explain the background?

Will this help you? Is it the same category.

[egunak95 (Aleksandr)]

Only PIXHAWK flight controllers have the ability to measure the VSERVO parameter

The screenshots show the graphs of the VSERVO parameter of the PIXHAWK4 and DURANDAL HOLYBRO flight controllers

[Jai.GAY]

@egunak95

Be careful, RC SB middle + pin supply voltage, exclude from the servo rail.

Servo or relay can be configured on the servo rail, get external power supply to operate servo or relay.

[geofrancis ([𝙂𝙚𝙤])]

as far as I know none of the 30mm boards have servo voltage monitoring, I think its only on pixhawk boards as its monitored by the pixhawk IO coprocessor and not the main H7/F4.
.
if your board has a spare ADC pin like airspeed or RSSI you could set it up as another battery monitor and use that to monitor the rail via a voltage divider.

[egunak95 (Aleksandr)]

You are right. It is enough to study the flight controller scheme. It’s so obvious

[Quaxwilly (Willy Zehnder)]

Thank you all for the quick and clear explanation.

Thank you for that hint @geofrancis I’ll try that workaround:

@geofrancis

if your board has a spare ADC pin like airspeed or RSSI you could set it up as another battery monitor and use that to monitor the rail via a voltage divider.