Backlight - EL vs LED

Post by **Romolo** » Fri May 04, 2012 6:27 pm

Numbers are numbers.... 2 leds in series = 5 or 6V voltage drop
the worst case 5V:
11V power supply - 5 V across the leds= 6V across the resistor
6V / 470 Ohm=12,7mA... That's all...

Post by **s_mack** » Fri May 04, 2012 6:51 pm

You are supposed to be someone who at least understads basic electronics.

I am??

To feed into a possible superiority complex, I'll inform you that my degrees are in Business Administration (marketing and HRM) althought I have never worked in the corporate world. My electronics expertise is limited and I never claimed otherwise. I have considerable indirect experience in the field but I am no engineer. But I do have some knowledge in the arena. As I already stated, I don't have the backlight (although, it may have just arrived! Box at the door) so I'm not sure why you just presume I'm going to know everything about it. You say its been "proven false by several people"... do you somehow expect that I read every single post out there or that I should somehow just simply know this?

Anyway, enough of this. I wasn't "feeding bs" and I honestly wasn't trying to mislead anyone to sell my boards. I really have always believed the backlight portion of the board was of minor benefit and I really don't care if people choose to use it or choose to use the LED. My declarations of efficiency were based on the manufacturer's claim and that's all. I don't think that's so horrendous of me to make my comparrisons based on their own literature.

Aha! My backlight did in fact just show up. So I'll see for myself. And I have no problem saying you're right if you are, in fact, right. Its such a minor point anyway. Its not like the batteries aren't rechargeable.

- Steven

Post by **Rob Thomson** » Fri May 04, 2012 7:01 pm

Boy... Lots of heat in this thread!

Basic fact is that it's all about choice, and Steve is looking at providing an up to date solution to help noobs get started. That is great and should be encouraged!

In the big picture... Does it really matter which is more efficient? To the average punter.. I guess not!

Steve... Re the sky9x board. Yes. I have a beta board - it has proved very good and is now my main radio

Rob

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Post by **s_mack** » Fri May 04, 2012 7:15 pm

That's awesome Rob. I can't wait until they hit the scene for real. That kind of power for that kind of price... wow!

OK, so it didn't take very long, now that I have an LED backlight in my hands (what timing!), to confirm what B12 said, no matter how rudely he said it. He's absolutely correct on the mA draw of the LED backlight. I'm baffled why HK would mislead so greatly... but I'm more baffled why they would do it against their own favor. Weird. Anyway, I am sorry I doubted your measurements and I hope you can understand that it really didn't make sense that they would OVER estimate their product's draw by six times. As for the "simple math"... I didn't know what resistor they had used. It wouldn't be inconceivable that they used a 100 ohm resistor. And maybe I should have read that somewhere and I probably should have found out before making statements... I thought I was safe sticking with their own claims.

- Steven

Post by **jhsa** » Fri May 04, 2012 7:32 pm

GGEEEE, guys, you should see the backlight I'm using in my radio.. By the noise it makes when it is on I would say it takes at least half ampere

It doesn't really matter as long as it works.. If I remember well Steven didn't even want to include a backlight.. He only did because people at the forum really asked for it a lot..

João

B12 · Post by **B12** » Fri May 04, 2012 7:34 pm

No offence taken. Hobbyking makes claims of tons of products, some are correct some are not. No hard feelings. I have no agenda whatsoever pro or con anybody, just the hard facts. In the lone fight against misinformation...

SkyNorth · Post by **SkyNorth** » Fri May 04, 2012 8:03 pm

The ERSKY board has gone through the Beta round of testing ....and no planes were harmed during the process.

I hope to do a production run of 110 boards the end of next week ....if all the parts show up...
So then I can start shipping tested / programmed boards , in a couple of weeks.

The Optrex LED backlight uses 30mA at 100% brightness on the ERSKY board according to the on board current sensor...

-Brent

Post by **Rob Thomson** » Fri May 04, 2012 8:17 pm

Are you going to give a choice of firmware on dispatch?

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Post by **Crucial** » Fri May 04, 2012 8:25 pm

What's the expected price of the new production boards? I've already got the LCD from digikey.

SkyNorth · Post by **SkyNorth** » Fri May 04, 2012 8:38 pm

They will be $95 and come with a pre-wired 8 ohm speaker , upgraded TO220 3.3V voltage regulator and heatsink.

As for which firmware ... IT could hold both ,and you could switch back and forth ..(Mikes Idea)

-Brent

Post by **s_mack** » Fri May 04, 2012 8:42 pm

lol, now you're just bragging!

Post by **MikeB** » Fri May 04, 2012 9:22 pm

On the subject of LED backlight current draw. I have some graphic LCD displays with built in LED backlights. The are specified as taking 100mA or so. I dismantled on of them, it contains 78 LEDs

, no wonder the current draw is so high.
Now it may well be that very early on, HK sold some backlights designed in this way, and published the 60-90mA figure. Currently they now sell a version with just 2 LEDs, the current draw is much lower, but they probably haven't bothered to update the current draw figure, so we, the customers, get confused.

Mike.

Post by **s_mack** » Sat May 05, 2012 3:01 am

I imagine a 78 LED array would provide a lot more uniform light though. That answers a question I was wondering about... I was going through LED driver IC datasheets and found one that was good for driving up to 90 LEDs in series and I was thinking... "when in the world..."

Post by **MikeB** » Sat May 05, 2012 8:34 am

I would be more uniform, except 39 LEDs are in parallel, in series with the other 39 LEDs in parallel, and only ONE current limiting resistor, so, unless the LEDs are matched, they have different brightnesses. They are also very inefficient LEDs.

Mike.

Post by **s_mack** » Sat May 05, 2012 2:37 pm

That is a strange one. Is it a particularly old design? I'm just curious about this thing

Post by **Crucial** » Sat May 05, 2012 7:39 pm

Here is a video showing the effects the EL panel has on the analog values when on.

http://www.youtube.com/watch?v=ifVxhbED ... ature=plcp

Post by **s_mack** » Sat May 05, 2012 7:51 pm

Well how bout that. Huh. Curious... why didn't you let me know when you first discovered it?? Not that its your job, of course. Just amazed I never heard of that before now. What revision of my board do you have?

Post by **Crucial** » Sat May 05, 2012 11:13 pm

I remember posting about it before but it's been a long time and I don't remember who it was with and how long ago it was.

I have the separate el driver board so I don't know if that ever had different revisions. Some one else posted about it here and might be using a full SP board. viewtopic.php?t=816#p10743

Post by **ShowMaster** » Tue Jun 26, 2012 7:33 am

Question for Steven.
Is it possable to post or PM me the led circuit and layout you now are using? All I want to do is modifying 3 version 2.2 EL boards to disable the EL driver and add the led get switch circuit you're now using. I've done my own mods but would like to add yours to be the same. I'm not interested in copying your work, just to bring the ones I own up to the current configuration and disable the EL circuit.
I'm not in a position to purchase 3 newer boards to replace what I now own. Maybe you have a daughter board for adding the updated led switch to your older boards?
Thank you
SM

Post by **Rob Thomson** » Tue Jun 26, 2012 7:43 am

Pretty sure that the wiki shows how to connect a led with a switch to the board direct.

sooooo... All you do is snip the trace on the board that leads to the pogo pin in question. Add an led and power source from the 5v...

Job done ale sense ?

Should be easily worked out if you look at the wiki led driver

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Post by **s_mack** » Tue Jun 26, 2012 2:53 pm

That's true Rob (sort of - its not quite as simplistic as you say because its not just a matter of connecting to a power source), but it isn't the same thing. The method employed on my board provides constant current to the LED and also, potentially (with firmware support), dimming.

SM - I will probably be releasing a standalone for Rev 2.1 users* (2.2 is the new one with LED support) because while it is simple and inexpensive, its one of those things that is much more simple and inexpensive if produced in quantity because some of the components come only in surface mount packages and that requires certain soldering skills a circuit board to solder them to.

- Steven

Post by **Rob Thomson** » Tue Jun 26, 2012 3:09 pm

Fair enough.

Although I guess if your goal is just to have an on/off switch.. then my idea would work

Rob

Post by **s_mack** » Tue Jun 26, 2012 5:11 pm

Yes if you mean a physical switch (ie. not controlled via the firmware).

Post by **Rob Thomson** » Tue Jun 26, 2012 5:54 pm

No... If you just do a firmware controlled on off switch as per the wiki.

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Post by **s_mack** » Tue Jun 26, 2012 6:03 pm

You got a link? Because AFAIK you can't just hook it up with "a switch" and expect control. There's a FET involved.

Post by **Rob Thomson** » Tue Jun 26, 2012 6:07 pm

Of course.

But that is what I have always meant.

If you follow the led switch guide on the wiki. And simply snip the trace around the pogo pin on the smartie board... You can disable the el backlight, add on Fet... And you are ready to go

I think we have been getting wires crossed

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gohsthb · Post by **gohsthb** » Tue Jun 26, 2012 6:09 pm

http://openrcforums.com/wiki/index.php/ ... ght_Driver

Post by **s_mack** » Tue Jun 26, 2012 7:30 pm

I gotcha Rob!

All you do is snip the trace on the board that leads to the pogo pin in question. Add an led and power source from the 5v

Made it sound (to me) that you power it directly as there's no mention of a FET. Also, the the HK design is intended to get power from battery voltage, not the regulated 5v power. It probably works fine on 5v, but it will be dimmer of course and potentially put strain on the regulator that wasn't designed to handle it.

- Steven

Post by **Romolo** » Sun Jul 01, 2012 10:45 pm

Personally I have placed the fet in and unusual place also taking the positive directly from the switch (i have placed a 330 Ohm resistor in series with backlight)

In this way it's also very easy to connect the gate of the fet to smartieparts pogo pin .

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