Raspberry Pi 3, problems with screen resolution using VNC

General discussions
Post Reply
Ian S
Posts: 7
Joined: Wed Jun 12, 2019 4:22 pm

Raspberry Pi 3, problems with screen resolution using VNC

Post by Ian S » Sat Jun 15, 2019 5:58 pm

I’m trying to set up a Raspberry pi to remotely control an RSP 2, I’ve downloaded the image and it works great locally. However when I use VNC to log on to the pi I run into a problem.

If I’ve got a monitor connected to the pi the VNC session opens in the same resolution as the monitor, which is good. However if I run the pi without a monitor, I.e. headless, VNC will only open at a default resolution of 720 x 480 and I can’t change it. This is far too small for apps such as Cubic SDR.

I’ve followed the instructions for changing resolution on VNC’s web site, I.e. editing the pi’s config.txt file. But whenever I run the pi headless with the SDRplay image it will only open at 720x480. If I boot my pi using a standard raspberry pi image I can set the VNC display to whatever I like in headless mode. It looks like something in the SDRplay image is overwrite is the pi’s config file to put VNC back to default.

Where do I look to get my VNC sessions for a headless pi running on a better resolution?
Last edited by Ian S on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
Reason: No reason

tolot
Posts: 2
Joined: Sun Aug 12, 2018 10:20 am

Re: Raspberry Pi 3, problems with screen resolution using VNC

Post by tolot » Sun Jun 16, 2019 12:15 am

sudo nano /boot/config.txt
fix "dtoverlay=vc4-kms-v3d" on "#dtoverlay=vc4-kms-v3d"
reboot
Last edited by tolot on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
Reason: No reason

sdrplay
Posts: 978
Joined: Wed Jan 07, 2015 7:58 am

Re: Raspberry Pi 3, problems with screen resolution using VNC

Post by sdrplay » Sun Jun 16, 2019 8:25 am

Note the above command will DISABLE hardware acceleration which is required for applications like CubicSDR to run properly. So use with caution.

Best regards,

SDRplay Support

Reason: No reason

Mr. Lucid
Posts: 3
Joined: Tue Jun 18, 2019 5:19 pm

Re: Raspberry Pi 3, problems with screen resolution using VNC

Post by Mr. Lucid » Tue Jun 18, 2019 5:40 pm

Hi,

tolot is correct in that you must edit the /boot/config.txt file. The following lines can be added/edited in the config.txt file:

#trick the Pi into thinking that something is connected to the HDMI port (use if running headless)
hdmi_force_hotplug=1

#force HDMI group 2 modes
hdmi_group=2

#force hdmi_mode for external monitor and VNC remote access
hdmi_mode=82

#for reference...
#hdmi_mode=81 sets a resolution of 1366x768 @ 60Hz
#hdmi_mode=82 sets a resolution of 1920x1080 @ 60Hz
#hdmi_mode=35 sets a resolution of 1280x1024 @ 60Hz
#hdmi_mode=16 sets a resolution of 1024x768 @ 60Hz
#additional configuration options are available here:
#https://www.raspberrypi.org/documentati ... t/video.md


Please note, when you force an HDMI mode using the above method, you not only force the resolution for VNC but also any monitor attached to the HDMI port. So, be sure the mode you select is compatible with your monitor if you intend to run the Pi with a display attached.
Last edited by Mr. Lucid on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
Reason: No reason

Ian S
Posts: 7
Joined: Wed Jun 12, 2019 4:22 pm

Re: Raspberry Pi 3, problems with screen resolution using VNC

Post by Ian S » Tue Jun 18, 2019 5:59 pm

Thanks for the replies. I’ve now got my VNC session running at 1280x1024, the same as when I have a monitor connected.

I’m in the process of setting up my RSP to be remotely controlled, am trying various things to see which works best for me.
Last edited by Ian S on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
Reason: No reason

Post Reply