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by PiGraham
Wed Sep 18, 2019 8:00 am
Forum: Advanced users
Topic: Real VNC server on windows 10 -- Real VNC viewer on Pi
Replies: 9
Views: 224

Re: Real VNC server on windows 10 -- Real VNC viewer on Pi

2. Can I use TightVNC, etc. with only local connections? (no internet) Yes, TightVNC works on Windows (client and server) on LAN (or WLAN) only. I haven't tried it on Linux or Raspbian specifically but I would expect it to work the same way. You give the IP address of the server to the client progr...
by PiGraham
Tue Sep 17, 2019 11:50 am
Forum: Camera board
Topic: HDR images
Replies: 5
Views: 173

Re: HDR images

Now I have to find the relationship between ISO, shutter_speed and EV. Does anyone has any idea? EV step of +1 is equivalent to halving the exposure time, all other factors being equal. So if you want +/- 2 EV around a nominal exposure time of 1/10 s you would use 25ms, 50ms, 100ms, 200ms, 400ms. h...
by PiGraham
Mon Sep 16, 2019 9:45 am
Forum: Media centres
Topic: Dual output for 3D stereo projection?
Replies: 20
Views: 311

Re: Dual output for 3D stereo projection?

OK. Cool.
by PiGraham
Mon Sep 16, 2019 9:40 am
Forum: Media centres
Topic: Dual output for 3D stereo projection?
Replies: 20
Views: 311

Re: Dual output for 3D stereo projection?

Hi i am very happy to see that Pi 4 has two hdmi output. Does it actually mean , we can use two different videos (left and right view for 3D) and play it in perfect sync? Or one full sidebyside video (3840x1080 or 2560x720) and playback to the extended display? Is it possible? If somebody could tes...
by PiGraham
Mon Sep 16, 2019 9:02 am
Forum: Camera board
Topic: HDR images
Replies: 5
Views: 173

Re: HDR images

I don't know the answer but the AGC system takes time to settle. Maybe 200ms is too little time. You may do better to manually set all parameters (exposure time, ISO, exposure_mode = off etc. Since you are building HDR it may be best to disable AGC and expose the entire roll of film at the same (3 t...
by PiGraham
Sun Sep 01, 2019 10:56 am
Forum: Troubleshooting
Topic: Permanently disable swap on Raspbian Buster
Replies: 70
Views: 4585

Re: Permanently disable swap on Raspbian Buster

Back to the original post. I can only think of a few reasons to disable the swap file, both dubious at best. - On a 4G Pi4, I've never seen it used at all, despite running it though its paces rebuilding the GNU toolchain with an 8 thread make (make -j8). - Disabling the dphys-swap daemon, might sav...
by PiGraham
Thu Aug 29, 2019 2:59 pm
Forum: Troubleshooting
Topic: Pi 4 power LED blinking while switched off
Replies: 14
Views: 461

Re: Pi 4 power LED blinking while switched off

This a logged, "known issue" and seems to depend on whether HDMI is left connected together with a USB C PSU connected but unpowered at the AC mains. This is a big issue for me, because I would like to use a remote controlled AC socket . But if the PSU is remain connected with one wire (the power s...
by PiGraham
Thu Aug 29, 2019 9:51 am
Forum: Troubleshooting
Topic: Pi 4 power LED blinking while switched off
Replies: 14
Views: 461

Re: Pi 4 power LED blinking while switched off

It seems voltage on the HDMI from the TV may be enough to just about light the LED on the Pi. If you remove the HDMI cable or unplug the TV from mains power does the LED stop lighting? Does your TV have an MHL HDMI port? These can provide power to charge phones while they provide HDMI to a device. Y...
by PiGraham
Wed Aug 21, 2019 10:35 am
Forum: Other projects
Topic: Need help on alert and tracking system
Replies: 2
Views: 356

Re: Need help on alert and tracking system

Hi, I need help in making my own tracking system similar like existing trackers out there. So my idea is to have build a tracker to be placed on an item (non portable ones such as desktop) so that I can monitor my item using Google Map on website I will create. For the alert system, how do I create...
by PiGraham
Sun Aug 18, 2019 8:47 am
Forum: Troubleshooting
Topic: Permanently disable swap on Raspbian Buster
Replies: 70
Views: 4585

Re: Permanently disable swap on Raspbian Buster

This outlines how swappiness relates to swapfile use when there is available RAM. What is the default for Raspbian? The default value of vm.swappiness is 60 and represents the percentage of the free memory before activating swap. The lower the value, the less swapping is used and the more memory pag...
by PiGraham
Sat Aug 17, 2019 2:29 pm
Forum: Troubleshooting
Topic: Permanently disable swap on Raspbian Buster
Replies: 70
Views: 4585

Re: Permanently disable swap on Raspbian Buster

You really have not understood how swap works. The swap file (or partition on some systems) reserves a chunk of memory on the SDCard Pedant mode: that's storage not memory. :) Though admittedly many folks confuse the two. Was that pedant mode flag a global? memory is storage, storage is memory and ...
by PiGraham
Sat Aug 17, 2019 2:22 pm
Forum: Troubleshooting
Topic: Permanently disable swap on Raspbian Buster
Replies: 70
Views: 4585

Re: Permanently disable swap on Raspbian Buster

The swap file (or partition on some systems) reserves a chunk of memory on the SDCard or SSD/HDD that can be used by the OS. That requires some startup time, but no run time. It is only actually used when the system runs short of RAM, which may be never. Are you sure that is the case? The Sysadmin ...
by PiGraham
Sat Aug 17, 2019 2:14 pm
Forum: Troubleshooting
Topic: Permanently disable swap on Raspbian Buster
Replies: 70
Views: 4585

Re: Permanently disable swap on Raspbian Buster

This is an interesting article on swap space. It may not negatively affect performance to have swap enabled, but I wonder if increases wear on an SD card even if you have enough RAM. I doubt you could measure the effect. I think writting all those log files in /var causes more wear and tear to the ...
by PiGraham
Sat Aug 17, 2019 12:37 pm
Forum: Troubleshooting
Topic: Permanently disable swap on Raspbian Buster
Replies: 70
Views: 4585

Re: Permanently disable swap on Raspbian Buster

This is an interesting article on swap space. Linux Performance: Why You Should Almost Always Add Swap Space We know that using swap space instead of RAM (memory) can severely slow down the performance of Linux. So then, one might ask, since I have more than enough memory available, wouldn’t it bett...
by PiGraham
Fri Aug 02, 2019 9:13 am
Forum: Other projects
Topic: Retrofitting an old projector
Replies: 8
Views: 2102

Re: Retrofitting an old projector

Google it It could be done with the official 7" touchscreen, for example, but there isn't enough light from such screens to give a very bright image. The reason for dismantling the screen and using a projector lamp is to get enough light. You would probably do better to buy a second hand proper pro...
by PiGraham
Mon Jul 29, 2019 6:41 pm
Forum: Beginners
Topic: Too many different voltages in my project
Replies: 19
Views: 665

Re: Too many different voltages in my project

So, how long does it have to be actively listening?
by PiGraham
Mon Jul 29, 2019 1:30 pm
Forum: Beginners
Topic: Too many different voltages in my project
Replies: 19
Views: 665

Re: Too many different voltages in my project

1.The sun is out, battery is charging on solar. Pi is either completely off or in super-minimal power consumption mode. Whatever lets me minimize the size of battery and solar panel. 2. Its dark out, or the project has been tricked into thinking so by covering solar panel and/or photoresistor if th...
by PiGraham
Tue Jul 23, 2019 10:49 am
Forum: HATs and other add-ons
Topic: HW to control 60 leds separately
Replies: 14
Views: 516

Re: HW to control 60 leds separately

If you do need to drive high power LEDs you could use the separate chip ws2811 and use that to control higher current switches.

Or you can use a higher supply voltage and put LEDs in series.

https://hackaday.io/project/8308-ws2811 ... ac/details
by PiGraham
Mon Jul 22, 2019 2:32 pm
Forum: General discussion
Topic: USB Webcam Appears as 2 Devices
Replies: 3
Views: 216

Re: USB Webcam Appears as 2 Devices

I am trying to use a USB webcam on the RPi 3 B+. I have been having issues with open cv when trying to access video. I typed "ls /dev/video*" to see the devices and the webcam appears as both /dev/video0 and /dev/video1. How can I fix this? $ ls /dev/video* /dev/video0 /dev/video1 /dev/video10 /dev...
by PiGraham
Mon Jul 22, 2019 12:17 pm
Forum: HATs and other add-ons
Topic: HW to control 60 leds separately
Replies: 14
Views: 516

Re: HW to control 60 leds separately

daylight visibility could mean different things to different people. One reviewer of the LED strings on Amazon I linked to wrote this: Used in a public LED display, handled bad weather without issue and clearly visible even in bright sunlight and the drivers respond to the WS2812 protocol without an...
by PiGraham
Mon Jul 22, 2019 11:01 am
Forum: HATs and other add-ons
Topic: HW to control 60 leds separately
Replies: 14
Views: 516

Re: HW to control 60 leds separately

I see you mentioned "if 1 watt per output is available" and relays
How bright do you need? That might limit your options.
by PiGraham
Mon Jul 22, 2019 10:14 am
Forum: HATs and other add-ons
Topic: HW to control 60 leds separately
Replies: 14
Views: 516

Re: HW to control 60 leds separately

Some configurations might make more sense wired as a matrix. Such as LED cubes.
http://ozzmaker.com/raspberry-pi-contro ... be-python/
by PiGraham
Mon Jul 22, 2019 9:23 am
Forum: HATs and other add-ons
Topic: HW to control 60 leds separately
Replies: 14
Views: 516

Re: HW to control 60 leds separately

I think the simplest option by far for 60 LEDs that are not tightly grouped is "neopixels" or "dotstars" Serial addressable LED drivers that only require one or two GPIO lines to control lots of RGB LEDs independently. You can get them on adhesive strips or wired chains (like Christmas lights) or on...
by PiGraham
Fri Jul 19, 2019 11:16 am
Forum: Automation, sensing and robotics
Topic: Project Idea getting feedback before I begin
Replies: 9
Views: 420

Re: Project Idea getting feedback before I begin

gordon77 wrote:
Fri Jul 19, 2019 10:50 am
PiGraham wrote:
Fri Jul 19, 2019 10:28 am



Basically capture still images of the board and sample pixel values in cells of a grid aligned with the lamps.

Just like I did in my example
Yes, like that, or some variant of that.
by PiGraham
Fri Jul 19, 2019 10:30 am
Forum: Automation, sensing and robotics
Topic: Project Idea getting feedback before I begin
Replies: 9
Views: 420

Re: Project Idea getting feedback before I begin

Burngate wrote:
Fri Jul 19, 2019 9:59 am

If you're turning a corner into a wing and see 6 doors with lights, then to find which came first could need a rebuild of the whole system.
Good points, but if the idea is to send notification emails those emails can give room numbers and times and a sorted list.

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