Using GPIO/I2C as pwm from voxl for payload

Aldo Castro Freire · 24 Jan 2021, 03:44

Hi guys, I wanted to avoid dealing with the px4 side of things to control a payload actuation, that requires a PWM modulation using LTE. Apparently mavsdk does not support control of a payload.

I wanted to know if this is possible in the voxl:
https://www.aranacorp.com/en/using-a-pca9685-module-with-raspberry-pi/
or this one
https://learn.adafruit.com/adafruit-16-channel-servo-driver-with-raspberry-pi/using-the-adafruit-library

Using the pca9685

modaltb · 24 Jan 2021, 17:56

Hi @Aldo-Castro-Freire ,

VOXL has an I2C port (3.3VDC logic levels) that you can use so in theory yes:

https://docs.modalai.com/voxl-i2c-io/

Let me know if you need more details, here's the port:
https://docs.modalai.com/voxl-datasheet-connectors/#j10-uart-or-i2c-off-board-external-sonar-or-imu-sensor

Aldo Castro Freire · 25 Jan 2021, 22:24

Thank you I can use that. One more question is it possible to implemented with the pca9865 that requieres a format like this one:

https://github.com/GuyCarver/MicroPython/blob/master/esp32/pca9865.py

If so, what method can I use to program it?

Aldo Castro Freire · 26 Jan 2021, 17:25

base on my research:
https://learn.adafruit.com/16-channel-pwm-servo-driver?view=all

Based on that we need to install
sudo pip3 install adafruit-circuitpython-pca9685
sudo pip3 install adafruit-circuitpython-servokit
would that be possible to do, or do have to run it on docker if so I am not sure on how to connect to external i2c ports

tom · 26 Jan 2021, 18:35

This isn't something we have tried. Python3 isn't on VOXL by default but you can follow the instructions here to get it going

Aldo Castro Freire · 27 Jan 2021, 18:11

How do I build the ipk image mentioned in the first step ?

tom · 21 Apr 2021, 16:37

@Aldo-Castro-Freire If you haven't yet, you will want to follow the steps here to get voxl-docker installed on your desktop in order to use voxl-emulator which allows you to build IPKs for VOXL on your desktop machine.

First you will run voxl-docker -i voxl-emulator
Then in the docker container you will run ./build.sh
Next, also in the container you will run ./make_package.sh
Create a directory to store ipks if you haven't adb shell mkdir -p /home/root/ipk
After, this you can exit the docker container and push the ipk to your VOXL with adb push Python_3.6.9_8x96.ipk /home/root/ipk/.
Lastly, you can install the ipk with opkg install /home/root/ipk/Python_3.6.9_8x96.ipk

Chad Sweet · 27 Jan 2021, 18:34

To be clear though, @Aldo-Castro-Freire you will still need to use voxl-io to communicate with the peripheral

Aldo Castro Freire · 27 Jan 2021, 19:06

@Chad-Sweet I am confused now, I thought the point of the library is that so I will not have to deal with the low-level logic. vox-i2c Basically I still wanna be using the pca9865 to convert to PWM that I can use to control
using this:
https://learn.adafruit.com/16-channel-pwm-servo-driver/python-circuitpython

right now I am not sure. how to connect those two together.

Chad Sweet · 27 Jan 2021, 19:30

Yes, sorry for the confusion, voxl-i2c is a part of voxl-io. You will want to use voxl-i2c to communicate with an i2c peripheral

Aldo Castro Freire · 27 Jan 2021, 19:36

My question is there a driver for pca9865 that I can use? Cause right now it seems I have not way of accessing the i2c port even if I use the libraries from adafruit.

So my question is can I run a python program that uses the i2c port to control the pca9865 that will allow me to control servos or payload actuation as an IoT device basically.

Chad Sweet · 27 Jan 2021, 19:38

No, that is not currently available. What you described would require coding in python to make the appropriate voxl-i2c calls per the pca9865 specification

Aldo Castro Freire · 27 Jan 2021, 20:00

Is there any other module that I can use to control something using the voxl. As I see I am not sure if voxl support any other devices.

Do you have any recommendations?
Looking for a way to trigger servos without having to install another computer.

MattO · 21 Apr 2021, 15:51

@tom said in Using GPIO/I2C as pwm from voxl for payload:

@Aldo-Castro-Freire If you haven't yet, you will want to follow the steps here to get voxl-docker installed on your desktop in order to use voxl-emulator which allows you to build IPKs for VOXL on your desktop machine.

First you will run voxl-docker -i voxl-emulator

Then in the docker container you will run ./build.sh

Next, also in the container you will run ./make_package.sh

After, this you can exit the docker container and push the ipk to your VOXL with adb push Python_3.6.9_8x96.ipk /home/root/ipk

Lastly, you can install the ipk with opkg install /home/root/ipk/Python_3.6.9_8x96.ipk

Hi Tom - I just wanted to let you know, after following these directions, I think there may be an error in the step for pushing the IPK to VOXL. Basically, what happened to me using the push command above, is that the contents of the Python_3.6.9_8x96.ipk file got put into a file named "ipk", and the reason is I'm pretty sure I did not have an "ipk" directory yet in /home/root (never pushed an ipk up prior to this). Basically, I had to delete the ipk file that was created, and mkdir an ipk directory in /home/root/. Then, I ran the command below to push the package, and the last step to install worked perfect.

adb push Python_3.6.9_8x96.ipk /home/root/ipk/Python_3.6.9_8x96.ipk

Might want to fix the instructions/README in the "voxl-python-3.6.9" in github too. Hope this helps!

Thanks

tom · 21 Apr 2021, 16:27

@MattO Thanks for the heads up! I will take a look at this.

tom · 21 Apr 2021, 16:35

@tom It's not required to push the ipk to a specific directory, that was just an example of a location that I like to use.

tom · 21 Apr 2021, 16:40

@MattO The instructions should be more clear now: https://gitlab.com/voxl-public/other/voxl-python-3.6.9#installing-the-ipk