hk backlight mod

General mods that are considered worth doing; regardless of the end firmware you use.
Camboui
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Re: hk backlight mod

Post by Camboui »

I like the idea of wiring the transistor directly without the backlight harness. Where do you get battery voltage and ground then ?
Also, is there a problem if I install a mechanical switch in parallel with the transistor ? (I believe it's OK)
Thanks

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Westy
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Re: hk backlight mod

Post by Westy »

there are a heap of Earth and +5V points on the board .... there are 5v regulators all over it! you can test for one ..... or let me know and I will trace some points you can get them from.
Cheers,
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Camboui
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Re: hk backlight mod

Post by Camboui »

Well, I understand the backlight is directly powered by the battery, not a regulated 5V.
I found this picture in another thread, the "batt v+" looks like a good source, right ?
Image


What about the switch in parallel with the n-FET ?
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Westy
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Re: hk backlight mod

Post by Westy »

so you want to run it off a separate switch entirely?.......

Depending on your back light colour. you can run it off any voltage over 3.3 and simply calculate the resistor needed to get the voltage through the resistor right.

you said you are not going VIA the harness that is supplied..... I think there are only 2 LED's in there anyway.
Camboui
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Re: hk backlight mod

Post by Camboui »

Instead of a resistor, a 15-20mA constant current switching regulator would be neat ;)

I'm OK to leave er9x control the backlight, but sometimes I'd like to turn it on permanently. That's why I want a parrallel switch with the n-fet.

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Malcurin
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Re: hk backlight mod

Post by Malcurin »

in er9x you can assign the light to any switch in the left menu thing down where there is also a timer and stuff including turning it off perm there i belive using one of the switches in that menu
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ReSt
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Re: hk backlight mod

Post by ReSt »

Camboui wrote: Instead of a resistor, a 15-20mA constant current switching regulator would be neat ;)
But don't forget, that the effectivity of a switching regulator is not 100%.
You may loose what you gain.


Reinhard
Camboui
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Re: hk backlight mod

Post by Camboui »

I looked at the bl and made measurements.
2 blue LEDs in parallel, R 470 Ohms.
LiPo 8.03V gives about 11mA and 2.74V at LED level.

It looks to me they're underpowered, assuming each LED can drive 20mA and reach the more nominal 3.4V level for a blue LED.
Even under 12V , total current would be about 18mA, only 9mA per LED.

About efficiency, the resistor of this blue backlight burns 65-75% of power, so less than 35% efficiency. Any switching reg can do better.
I have a spare HK switching 3.3V regulator. I may try it.

EDIT
LiPo 11.89V gives about 19mA and 2.82V at LED level. Internal LED resistance is about 10 Ohms.
3.3V regulator and 22 Ohm is ok for the bl. The same regulator can be used for other things, like the DSM mod.
Last edited by Camboui on Mon May 14, 2012 8:06 am, edited 1 time in total.
Camboui
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Re: hk backlight mod

Post by Camboui »

Malcurin wrote:in er9x you can assign the light to any switch in the left menu thing down where there is also a timer and stuff including turning it off perm there i belive using one of the switches in that menu
That's one switch less for programming. But OK, I could never have to use them all.
Gladiac
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Re: hk backlight mod

Post by Gladiac »

Hi all!

I have just one question :D
I tried to do this mod on a friends flysky version 1 tx but it wount work :(
Do i need to use diferent pin on this bord?

Thanks in advance for your trouble :D

Uroš
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Westy
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Re: hk backlight mod

Post by Westy »

Hey ...
has anyone checked the voltage supply to the Backlight? ...... what voltage is it?

If I was to use 5Volts .... with a white HK backlight.... what resistor would I need?

ANyone?

I am modding a DX7i SE wit hthe backlight kit .... it has a 470ohm resistor accross it.

cheers
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Kilrah
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Re: hk backlight mod

Post by Kilrah »

The BL takes the battery voltage, i.e. 7-13V depending on how people power their radio, and of course with a different bightness along the range :)
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Westy
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Re: hk backlight mod

Post by Westy »

Cheers..... So if I was to use an 8VDC rail feed .... I would have to drop the resistor to what to maintain the same brightness as the 470 ohm one installed?
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Westy
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Re: hk backlight mod

Post by Westy »

I calculate it for a 270 ohm resistor .... should do the trick for 8VDC. ...I only have a 360 SMD ..... but may find a lower rated ceramic one lying around......
Camboui
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Re: hk backlight mod

Post by Camboui »

LED voltage is 2.84V under 19mA current on my blue backlight.
I will use a 3.3V regulator and 22 ohm: constant brighness regardless battery.
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Westy
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Re: hk backlight mod

Post by Westy »

I have a perfect 5V plug on the DX7i SE...... so perhaps 100ohm?
Camboui
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Re: hk backlight mod

Post by Camboui »

I would say 120 Ohm, but 100 Ohm should be OK.

I did the mod this WE with 3.3V, 22 ohm and a blue backlight. It's bright, maybe too much !
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Westy
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Re: hk backlight mod

Post by Westy »

I finally complete my mod to the DX7SE .... lot of hard work and totally had to re-engineer the HK backlight and LED arrangement to get it to all fit in there small space .... but I am over the moon on the result!
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Re: hk backlight mod

Post by sterby »

I have a bit of a problem here. I did the BS170 MOSFET mod for the backlight, but at first it looked like it worked inverted as the backlight turned on after the Light Off timer was set.
In a bit of dark it looks like the BL is always on and with very dim when it should be ON and full bright when it should be OFF. In what condition could this happen?
It seems like I did everything right, every connection is secure and in the right place, no short circuits. Where the leads have to be cut, are definitely cut, no short.
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Re: hk backlight mod

Post by jhsa »

picture/s??
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Camboui
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Re: hk backlight mod

Post by Camboui »

I would say BS270 pins are out of order. A picture or at least a diagram of your connections might help.
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ShowMaster
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Re: hk backlight mod

Post by ShowMaster »

HK White Backlight current draw vs. voltage applied 5-13V
The stock backlight has 2 leds wired in series with a 470 ohm resistor to limit current.
TX battery voltage/current draw.
5V = 5Ma
6V =7Ma
7V = 9Ma
7.4V = 9.8Ma
8V = 11Ma
9V = 13Ma
9.6V = 14.25Ma
10V = 15Ma
11V = 17Ma
12V = 19Ma
12.6V = 20Ma
13v = 21Ma
Brightness of the backlight does depend on TX battery voltage used. The brightness at 7.4V was more like the stock EL on the SP board. At 9.6V to 12.6V the brightness was much brighter. !2 volts was a little brighter than 9.6-10V but the current went up to 20Ma. I use a LiFe 9.6 volt HK battery so I’m going to use 14.25Ma as my final current constant .My metering of course may have some difference in accuracy but should be close enough for most. 
For those using a 2 cell 7.4 type battery setup you may want to lower the 470 ohm resistor to allow the current to be 14Ma as the brightness increase is noticeable.
Hope this helps settle the current draw questions we all had.
If you install this BL note that a circuit board wiring error exists that stops the Trainer out/Simulator  PPM signal from working. It requires a circuit trace to be cut and a jumper to be added.  
http://www.rcgroups.com/forums/showpost ... ount=12455
Camboui
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Re: hk backlight mod

Post by Camboui »

ShowMaster wrote:...
The stock backlight has 2 leds wired in series with a 470 ohm resistor to limit current.
...
I think they are parallel, not serial.
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Re: hk backlight mod

Post by Greebo »

I wanted to ditch the in-line connector and switch the light from software so here's how I did my backlight mod...

HobbyKing Green LED backlight kit with the LED wires unsoldered from the in-line connector board.
I just happened to have a 220 Ohm SMD resistor I scavenged from another dead board so that is soldered in-line under the red heat shrink.
The voltage comes from a convenient 5V pad and the FET is soldered directly to a ground pad.
I added the connector just in case I needed to detach the backlight for more mods to the board :)

The current draw is about 9mA.
IMG_4687.jpg
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Re: hk backlight mod

Post by Romolo »

on 5v you don't need any resistor as the led are serially connected
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jhsa
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Re: hk backlight mod

Post by jhsa »

The LED backlight from HobbyKing? I think is parallel.. hence the 150 ohm resistor on the voice board to drive the NL
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ShowMaster
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hk backlight mod

Post by ShowMaster »

The HK LEDs are 2 wired in series.
I posted this way back but it may help.

Hobbyking backlight
I did some quick math to add a resistor in the BL red lead. My board has the 2 100 ohms in parallel so I end up with 50 ohms. Using a led drop of 1.3v for white leds x 2 =2.6v. Take that from 5 volts max available and that leaves 5-2.6=2.4v to drop. Using a safe max current value of around 12Ma I came up with 200ohms. I added a 150 ohm in series with the onboard 50 to get the 200. My backlight looks as bright at full as my BL running on 9.9v with the stock 470 ohm. I'm happy with the current draw from the regulator and the brightness. To just wire the BL to the board may only put 50-100 ohms series limiting and could damage the LEDs and tax the regulator at max brightness is my thinking.
Hope this helps those wondering what to do to be safe.

Brent did respond with the fact that the LEDs are PWM driven but I think some limiting is still needed.



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Greebo
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Re: hk backlight mod

Post by Greebo »

I played around with resistor values on a breadboard before I did the work. The 220 Ohm resistor at 5V gives me about the same brightness out of the LED's that I got by plugging in the harness with my LiFe battery so that's what I went with (and I had one handy).

I was just showing an alternate connection method for others, not starting another war on series vs parallel or what resistor to choose... Resister discussion has been done to death here already anyway :)
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Re: hk backlight mod

Post by flynbrian »

Wow I just read this entire thread until my eyes have bled. Here is the deal today I finally received my HK blue backlight along with the frsky DIY conversion. At this point I have the turnigy 9x tx and a smartieparts programmer . By tomorrow I will have the atmel usb avr programmer. With that said what is my best choice. Keep in mind that I am perfectly competent with a soldering iron. Is there a problem with the smartieparts programmer and the backlight?
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Daryoon
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Re: hk backlight mod

Post by Daryoon »

Thanks Greebo. I like your method better than the method that have been shared before you. Your way means I can reuse the connectors as a port for the programmer. :D

BTW, serial or parallel...here's a macro shot of the LED circuit board. It looks like the LED are in parallel to me.
Image

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