Want to control LED brigtness over several boards from 1 point. - Page 1
Forum section: electronics / beginners

author: v81
author_rank: Regular Contributor
timestamp: October 01, 2020, 02:05:54 pm
content: Hi there..I'm working on building a flight sim cockpit made from multiple button panels and would like to control the brightness of LED backlights on all panels from a variable (0 - 65534) in an arduino.Clearly a single pin will not tolerate the load of what would be a total of 100's of LEDs.Was wondering of there was a clever way of building the back lighting into each board as series strings of LEDs driven by the 12v supply on each sub board, and have brightness controlled via a PWM signal distributed around the pit from a single Arduino.I'm not terrible with code, but I'm not smart with semiconductors so witht he above background info..1) Am i likely to have any issues with signal integrity from the PWM pin running a signal over up to 3m/9ft distance?2) Would this be best achieve with a MOSFET or transistor on each sub board driven by that PWM signal or is there another way?If there is any info on how one might go about this it would be much appreciated.Cheers.

author: ledtester
author_rank: Super Contributor
timestamp: October 01, 2020, 02:50:39 pm
content: "individually addressable LEDs" such as the WS281x might be a way to go:http://www.thesmarthomehookup.com/the-complete-guide-to-selecting-individually-addressable-led-strips/Pros: easy to use, very simple circuitry, can achieve full RGB colorsCons: more expensive per LED than plain LEDs

author: David Hess
author_rank: Super Contributor
timestamp: October 01, 2020, 05:19:31 pm
content: Quote from: v81 on October 01, 2020, 02:05:54 pmNo, that can easily work at the frequencies involved. The PWM frequency does not need to be very high and filtering can be used at the source to limit the bandwidth or edge speed reducing inference. However higher PWM frequencies have the advantage of making interference on the power supply side easier to filter; see below.QuotePWM has the advantage of high efficiency however a linear design removes all possibility of interference. I have done what you suggest with low frequency PWM of large LED displays and switching artifacts were a problem on the high current LED supply. Whether a linear design where say a relatively high but low current control voltage controls many current sinks which drive the LEDs is suitable will depend on your efficiency requirements, but efficiency can be still be good because the voltage drop across the current sink driving each LED array can be small.

author: v81
author_rank: Regular Contributor
timestamp: October 02, 2020, 09:18:26 am
content: Quote from: ledtester on October 01, 2020, 02:50:39 pmThis might work, honestly hadn't thought of them.The physical size vs 0603 could be an issue in addition to the cost.Thing is though this does solve all my probelms.You've given me something to think about.Quote from: David Hess on October 01, 2020, 05:19:31 pmSounds like this has potential.This is a fighter cockpit for myself and 2 friends, so overall number of LED's will be quite a few, in the realm of 100 to 200 per cockpit.Haven't done the math yet, each sub panel of the cockpit will be a USB HID device, firmware and drivers not mine, supply will be 5v for the HID stuff via USB.The output stuff will be driven from something called DCS BIOS, and open source bit of kit that we intend to drive cockpit displays with (radio freq, warning lights, backlighting etc..).DCS BIOS has an Arduino library so this sounds like the best solution for us.Regarding power we're considering an additional 5v supply or a powered hub, for the lighting i was considering adding a 12v supply and a 12v rail/input on each panel thinking 12v might be better, and then run the LED's in series, thus minimizing cable losses running power to each panel.I've never scratch designed anything with mosfets or transistors before, so I'll need to read up on that, any advice would be great.

author: drdm
author_rank: Contributor
timestamp: October 02, 2020, 10:42:28 am
content: Do you have a rough estimate on how many groups of how many LEDs you need to control? A little bit more specific information about the power supply would be useful.Also it is important to specify if you plan on building and ordering a custom PCB or if you want to use a prototype board and solder everything by hand.There are a lot of integrated LED drivers which incorporate current sinks and boost converters and are designed, for example, for automotive, thus providing EMI features.In my job we use a lot of Texas Instruments stuff, so you can look there. Even if they are not in a DIP case you can use a breakout board if you don't want a custom PCB.Most of them are controlled by SPI or I2C so the pin count on the Arduino will not be an issue.

author: Psi
author_rank: Super Contributor
timestamp: October 02, 2020, 11:10:07 am
content: You can have a common negative bus that is PWM brightness controlled and goes to all lights in the system. Then switch the positive on/off to enable each LED locally per module.It's a bit more complex but you can also have the negative PWM at a very fast rate and then do much slower PWM on the positive side locally.So you have a master brightness control for everything but can still do independent local brightness control per module.

author: v81
author_rank: Regular Contributor
timestamp: October 19, 2020, 03:23:29 pm
content: Quote from: drdm on October 02, 2020, 10:42:28 amTotal will be around the 100 - 200, think back lighting for panels in a fighter cockpit.Panels will be in 3 - 5 groups.Doing my own PCB's, components will be surface mount (preferred).Was thinking of having a lighting cub circuit on each panel with a PWM input driving a transistor or mosfet or something.Not real clever with semiconductors, probably shows.Power supply on 2 of the smaller groups is 5v via powered USB hub or DC jack.Remainder is flexible can be 5v, though i thought a higher voltage might be more efficient.PSU in that case would be a 12v DC power supply.Had also considered a DC jack on a PCI bracket to take the 12v from a PC.The project already contains an Arduino Mega 2560 that already talks to the flight sim and can get sub panel brightness data as a variable.1 'Panel' will be left / right console (thus interest in carrying a signal over to the other side of the cockpit), another will be engine instruments, another will be another type of instruments etc...Not an ideal picture as most of the lighting is ion the left and right consoles, but this might give the idea.Backlighting would be for buttons and/or button labels depending on panel.

author: v81
author_rank: Regular Contributor
timestamp: October 19, 2020, 03:25:43 pm
content: Quote from: Psi on October 02, 2020, 11:10:07 amThis is pretty appealing as if i can't get even brightness across panels tweaking on a per panel basis would be handy, even a simple trimmer or something to adjust each panel would be good.Apologies to both of you for the slow reply, i need to get my eevblog notifications sorted.