openrcforums

like title said. i did the backlight mod to my turnigy 9x wit an AT128 but the backlight stays ON all the time no matter what setting i do on the radio setup menu( ie: backlight mode OFF and still the backlight is ON). please a little help.

ps.
using the following file:
opentx-stock128-templates-audio-voice-haptic-DSM2-ppmca-battgraph-ttsen-en

TIA
magnetus

How did you connect the backlight? did you connect it to a FET transistor? and the transistor to pin 17 of the atmega128?
Do you have the smartie parts board?

Tell us a bit more about your mod so we can understand what you did. the more info you give, the better we can help you

João

Programmer is a cheap ebay one.
I connected a fet bs170 with the gate at pin 17 drain to ground and source to the negative of the backlight . Positive of backlight to a 470 ohm resistor to a 5v line.

No, DRAIN goes to the negative of the backlight.. SOURCE goes to ground..

João

thanks. i used a new fet just to be sure and connected gate to pin 17, source to gnd and drain to negative and still have the same issue. no matter what setting i have in the backlight menu its stays always on.

You have selected voice in you build for a stock TX (M64/M128). This requires you to add a voice module (Emartee or Megasound). These modules use pin 17 differently and move the backlight control onto the voice module.
If you haven't got one of these modules fitted, but do have voice selected then you lose backlight control.

Mike.

ok. thanks mike, now i create and download another firmware without voice, replaced the fet again and it works but backwards, i set up backlight on keys for 5 seconds. backlight is always on and when i press a key it goes off for 5 seconds. im going crazy,,,,

is there an option in the settings somewhere for backlight invert? I know it exists in Er9x.
-Gohst

If you disconnect the gate and short it to ground does the BL go off?
Is the FET actually working like a switch?

if i connect the negative of the dl to pin 17 seems to be working but it never turns off, it goes bright after i press a key and dim after timer off ( 5 sec)
Gohst --> loaded Er9x firmware and invert backlight and it works. lights on for 5 sec.

Hmm there's something very strange here..

Are you sure you have theFET SOURCE to ground and DRAIN to the backlight negative wire? the positive BL wire (red? ) goes to the 5V?

João

100% sure. bl red to 470 ohm resistor. drain to dl negative, source to gnd and gate to pin 17

magnetus wrote: Gohst --> loaded Er9x firmware and invert backlight and it works. lights on for 5 sec.

Ok so the hardware is working correctly then, now someone just has to figure out Open9x.
-Gohst

Are you selecting the SP22 option when you download the opentx firmware with companion?
If you don't have the smartie parts board you should not select that option..

No im not selecting sp22 option

Your BL is wired this way and your are able to control it on or off by shorting the gate to +5 or ground?
If so it's a menu selection issue or a bad FET.
It has to work.
You are on pin 17 for sure?

Check right corner orange wire for pin 17 connection. Any pictures of your wiring please.

The backlight connection can also go directly to the pad as shown in the image below.

connections are good, i am able to use the backlight with er9x but i have to use the invert option.

ShowMaster --> 100% sure im on pin 17

Flaps 30 --> i measure the trace and its ok and actually i am connected straight to pin 17

What's the voltage on pin 17 when the normal non invert option is used and you tell the BL to be on?
On should be +5v on pin 17, off should be pulled to ground. No matter what FET your using does. If you need to use the invert I still think something's wrong?
Is it posable the fets your using are mislabeled and are P channel?
The FET should saturate when +5 is on the gate and cutoff when a low or ground is on the gate. I've modified 10 TXs for BL control using the BS170 or 2n7000 FET and never needed the invert option.
If it's working for you ok then I guess you go with it but not knowing why it requires the invert option would drive me nuts, or more nuts.

Just for reference, the BS170 and 2n7000 have different pinouts if replacing one with the other you will have to turn it around..

João

Yes on the two fets having different pinouts. The gate action however acts the same. 2n7000's stocked locally and I have to order BS270's so it depends on my stock. The BS170 can handle higher current.
II still am confused by him having to use the invert option?
It's got to be a FET issue?

are you sure you didn't check the SP22 option when you downloaded opentx with companion? because that is what that option does.. inverts the backlight..

João

You're probably on to something Jhsa.
Until we know what pin 17 is reading when the menu is set to BL normal we'll never know if it's the FW or the FET circuit. Then we can work to correct it.

In the openTx file line he listed earlier, sp22 is not listed. So he didn't check that option in companion.
-Gohst

using this configuration: opentx-stock128-templates-audio-DSM2-ppmca-ppmus-dblkeys-battgraph-imperial-en

voltage at pin 17 is 2.9v at all time
and 0 when I press a key. that's using opentx (non inverted)
back to the old problem. backlight on all the time, off for 10 sec when i press a key.

ps.
im using this fet
http://www.ebay.com/itm/221267263749?ss ... 1439.l2649


checked my fet polarity and its hooked up as in the diagram.


using er9x inverted 0v all the time and 2.9 upon key press

So your FET circuit just happens to work inverted. Just tick the sp22 option in C9X and reflash, this will invert backlight control and you'll be good.

I think the voltage from pin 17 should be higher. It should be much closer to 5V, the same voltage the processor is running from. If it isn't then I think there must be an extra load on the pin. A FET doesn't draw much current so the load shouldn't be coming from that. Do you have a picture of your installation?
-Gohst

I tried sp22 setting and works normal.

I have a similar problem with my backlight after transistor mod.
Instead of completely turning off.. the backlight just dims to about 1/3 brightness. It never goes off completely. Everything else is working as it should.

Any ideas why?

Check you connections to the FET transistor.. I don't know which one you used or which guide you followed. knowing that would help to find the problem. Normally that indicates that the transistor is not well connected.

João