CAM_FEEDBACK_PIN output 3.3V when it should not

I have a plane with Pixhawk where I use the shutter throught a circuit with 2 transistor, it works perfectly, now I want to use the CAM_FEEDBACK_PIN feature with a cable I made for the Canon S110 with a photoresistor that input 5V from PIN 102 and output 0V normally and 5V when the camera get picture hooked to an AUX channel set in the software by CAM_FEEDBACK_PIN.
The cable works very well if I test with external 5V supply but when hooked to the pixhawk it doesn’t, so I have attached a voltmeter to the cable and discovered that when i set CAM_FEEDBACK_PIN 5x (tested 51 to 54) and test if it works clicking on “Do Action” “trigger camera now”, the pixhawk immediately outputs 3.3V to the PIN I set with CAM_FEEDBACK_PIN, the 3.3V stay there until I remove battery, connect battery again and it goues to 0 Volts, click again on “Do Action” “trigger camera now” and goues to 3.3V.
I hope I have explained well myself.



I have tried to set RELAY_PIN2,53 and CAM_TRIGG_TYPE, 0 but same problem

Thank you

Am I the only one using this function in PLANE 3.7.1 ?

Are you using a similar cable to this?:

I’m using this cable and it works flawlessly with 3.7.1, let me know if I can be of any help.

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Thanks for the reply, I bought a cable for Sony from tuffwing but not the cable for Canon, so I made my own, can you share your parameters file?
Thank you

Sure, I’ve attached my parameter file in this message.

For reference, the cable that triggers my camera is connected to AUX3 (RC11), the cable that reports when the camera shutter opens is connected to AUX1 (RC9)

What is the value of BRD_PWM_COUNT in your plane?

Here is the parameter file:
plane.param (11.3 KB)

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So it seems whe are using one of the 4 RC ports, not the 2 digital I/O (54 AUX5 - 55 AUX6)

Thank you

Perhaps it would be worth it to try the following configuration

connect feedback cable to AUX1 (RC9) or AUX2 (RC10)
set CAM_FEEDBACK_PIN = 50 or 51
connect trigger cable to any AUX that isn’t AUX1 or AUX2
set RELAY_PIN according to the previous choice
configure rest of parameters according to your specific setup

This configuration also worked quite well for me

a few notes:

  • I had to reboot my flight controller after changing BRD_PWM_COUNT
  • you can set LOG_DISARMED = 1 to diagnose CAM and TRIGG messages in your logs
  • I read somewhere that pin 54 has a lower latency compared to the other pins, but I never managed to get the feedback function working on that AUX port for some reason
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I set this:

put a voltmeter on the signal pin of the pin 51 and as soon as I click “trigger camera now” it goes to 3.3V

tried to set CAM_FEEDBACK_PIN 53 with the same result.

Maybe I am wrong on how it works eletrically, that’s what I think:

The pixhawk reads the voltage variation on the CAM_FEEDBACK_PIN, so I connect the 5V from the center pin to the photo diode, then connect the other leg to the CAM_FEEDBACK_PIN, when I take picture it goes from 0V to 5V, the problem is that the CAM_FEEDBACK_PIN actually feeds 3.3V so there is no way to monitor the voltage as is not acting as an input pin

I took another pixhawk, identical to the other 2.4.6 (with the 1MB limit) and I made a video to better explain, I am measuring on the PIN 52 wich is the CAM_INPUT_PIN, you can see as soon as I call the first shutter it goes and stays at 3.3V.

Set the volume to low because there is some noise.

thank you

It seems the error is feeding 5V when it only needs to close the circuit between the pin with 3,3V and ground, with a resistor, tomorrow I will check

Problem solved: I made a simple cable with ground and AUX (CAM_FEEDBACK_PIN) with a TIL 78 phototransistor and added a 1K RES in series between AUX and the phototransistor.

The log shows the exact number CAM messages but the TRIG are doubled, don’t know why but I don’t need that

This cable works with a Canon S110 and CHDK, the HOT SHOE version is different, I suggest buy from Tuffwing


I tried to reach out to Tuffwing to purchase their Canon geotag cable but unfortunately received no response from them. And I need to use the cable urgently. Thus I have no choice other than to make my own cable.

I’m fairly new to electronics, and I would like to seek your help in building the same cable.

Would you mind sharing how you made the cable, such as parts needed, diagram and how you wired all the parts together.

Your help is greatly appreciated.

Thank you.