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G3X and GTN 650 lighting / dimmer control

TShort

Well Known Member
I'm in the process of installing a 3 screen Garmin system (GDU460 x2 and a GDU450) plus a GTN 650.

In terms of dimming / lighting control, the G3X install manual states:

"For providing this reference signal to more than one device, a commercially available regulated backlight voltage reference is recommended."

I found reference to this for dimming the GTN650 in previous posts:

https://www.digikey.com/product-det...s-corporation/RV6NAYSD103A/RV6N103C-ND/222834

Can I use the same potentiometer to dim the GDU screens? Are others just relying on the automatic dimming, and just having a panel mounted dimmer control for the GTN?

Not sure the best way to handle this.

Thanks in advance.

Thomas
 
PWM dimmers need a filter

I used the PWM dimmers to control G3x lighting- it didn't work well . Particularly at lower levels the display light level was unstable. Adding a simple RC filter solved the problem. PWM dimmers are effectively digital dimmers providing a variable width pulse, most lighting control inputs are expecting a true analog voltage.
-Greg
 
I too was going to install separate pots for my Garmin devices as I had the GAD27 with PWM to vary device lighting. Everyone I subsequently spoke with who had GTN650's installed were quite satisfied running of their internal photocells. Thus the only 10k potentiometer I am now installing is the one for Van's LED lighting strip and and all the Garmin devices (GDU460, Aera 660, G5, GTN625, GTR200) are running off their photocells, however I have reserved space in my panel for post if required in the future, but frankly I'd prefer to rely on the photocell as it's one less thing to think about when flying, and when maneuvering the lighting intensity can change quite significantly on the panel as a device goes into or comes out of shadowing.
Tom.
 
Thanks for the input.

I had wondered if I could rely on the photo cells to adjust the brightness, but am about to have the panel cut and wanted to add the hole for the potentiometer if necessary.

All I have are the GDU screens, the GTN 650, and a G5, so I guess I could just rely on the internal auto adjust...

I'd read about the FDS boxes, but want to keep things as simple as I can, and would like to avoid mounting another box (things are getting crowded)
 
If you're electronics inclined, a simple emitter follower transistor buffer (two components), or a simple unity gain op-amp (one component) would be all that's needed to buffer the output of the pot to supply a low impedance voltage to the G3X and others (I'm building a similar setup).

The pulse width modulated (PWM) signal is NOT the correct one for this HW, but as noted by Greg, a RC low pass filter would serve to convert the PWM into a pseudo-analog signal.
 
I always install simple 10k pots for dimmers on big screens and GTN's.

All 3 G3X screens be dimmed from the same pot then another one for the GTN. Flying at night with a screen that is too bright or dim is not the time to try to be setting up an internal dimmer IMO, nothing easier than twisting a knob and setting the brightness level exactly where you want it.
 
Walt-

So the dimmer referenced in my first post would work (I copied that from another thread where you referenced the dimmers)?

Just connect it to the lighting control pin(s) on the GDUs and /or the GTN, and that's all that is needed? I'm just not 100% clear on how things are connected.

Thanks
Thomas
 
Walt-

So the dimmer referenced in my first post would work (I copied that from another thread where you referenced the dimmers)?

Just connect it to the lighting control pin(s) on the GDUs and /or the GTN, and that's all that is needed? I'm just not 100% clear on how things are connected.

Thanks
Thomas

Yes.
One end of the pot to 12 volt power (fused or CB); other end to ground; middle ?slider? to GTN(s).
 
I'm in the same boat, with the same questions. I'm going with Walt's recommendation.

Thanks Walt for your contribution to this site as well as the excellent customer service you always provide through EXP Aircraft Services.

Ryan
 
The GAD27 has three dimmer inputs to drive 3 PWM and 3 Analog dimmer outputs to the devices. So if you have that device then you wouldn't need an external PWM device? I thought that was so.....

On my panel I have two GSU, GMA (com panel), GTN 650, and the autopilot GMC307. Add the Vans LED light strip (red/white), and possibly some warn/caution/pump lamps won't the GAD27 drive everything?

Is the dimming of the GTN650 so different from the GSU that each should have it's own dimmer?
 
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The GAD27 has three dimmer inputs to drive 3 PWM and 3 Analog dimmer outputs to the devices. So if you have that device then you wouldn't need an external PWM device? I thought that was so.....

On my panel I have two GSU, GMA (com panel), GTN 650, and the autopilot GMC307. Add the Vans LED light strip (red/white), and possibly some warn/caution/pump lamps won't the GAD27 drive everything?

Is the dimming of the GTN650 so different from the GSU that each should have it's own dimmer?

Hello JDA_BTR,

You are correct that the GAD 27 has 3 DC reference voltage backlight buses to control devices like the GDU 4XX displays and GTN 6XX/7XX as well as 3 PWM drivers to power devices like LED strip lights (500 mA max).

You can control your GDU displays and the GTN from the same DC lighting bus, but since you have multiple, it is probably better to use them. Note that even if you use all 6 lighting buses, you can control them from a single 10K potentiometer if you like.

IPrr1O6IZpVCehMkAbJCUOcsGsBc6Yv3Z4Xa5ctodd39N-H7B6tv-cFT979f1CUuP2CfinoSPsFTs8UNv5t-S_0Lg8JFbVV7oRToCarfuYza655Mo-kZWQbEBJEQYUEr-3gqUZhIYHO5nr0XSnu2uZIWFSXwLVZo6R33YmY3ily0RoUbIZ6DbAXRuBkAyCmK_gRrC4xHcd-1WL76fT6qWyDimxTVT5xgR9fmrFx_XLq7miqxDOp5dsbNHhMfAzSsnhRNfND6l24GZKgvA13D38OcCnfE8GxvknQyNPx0VLCHYdlvexW4Ut4-_sb1o86YWH2TKNQA-4wm5Fpq5kUBu-sMYMZDXOdj706_amd2I7uzbIYdsFFZSwZkoJRxa9XwMs4tiN45gFHZidIZGWTgRy2R6MkFRE9gdemCd5L3CXA1qhLt6VEvpq-HG54XNepe5I5uy69hvvksBE6rfAM8nkD6WEDOTtVVsswBF6puNfoeghZ-FOe7qexq87winIiZtWt1fXm8NJNv8Hb4XA3ahEkZnsADJ9fbOKxGV0Uy8kXEzOl0V_bBGMlDxCstntUQHth8wVOfjwv5TRcveLYCzgzCHxtBLAA3jbe_5Khu_w=w920-h473-no


Page 26-14 of the Rev. AC G3X Installation manual provides this example for connecting most of the commonly installed devices in a G3X Touch system.

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Thanks,
Steve
 
Just one approach ...

I installed a GAD 27 and 3 pots. #1 controls the screens (2 x G3X, GTN 650), #2 controls switch lights (LED lit switches) and buttons on the audio panel and GTN 650, and #3 controls the glareshield LED in red (flying) or white (ground/cabin). Both #2 and #3 are programmed to be able to go to zero and extinguish the lights - gives me a dark panel except for screens for cruising. I?m very pleased with the final result as it gives me all the control I wanted.
 
The dimmer control function of the GAD 27 for LED circuits works by pulse width modulation of the ground side of the circuit. I supply power to the red LED from a ?panel lights? switch that also powers LED lighted switches. I supply Power to the white LED circuit form a ?cabin lights? switch that also Power an LED light in the baggage area. If both cabin lights and panel lights are turned on (I don?t do that, but could), both colors are illuminated.
 
Makes sense. Can you send a pic of the baggage area light you used and where the cable runs to it? One PWM for both red and white, using one at a time. I suppose you could use both at the same time you wanted.....
 
JDA_BTR:

Here's what I used:
(photo 1)

and it's very simple wiring:
(photo 2)

In retrospect, the grommet could have been under the light for a cleaner install. I ran the power/ground back through the roll bar brace to the baggage wall and down to the molex connectors in the baggage wall bulkhead. I used 2 "extra wires" in the main fuselage harness (from Van/Stein) - I think maybe called data channel C - that got me to the panel and tied in in the switches.

The "Cabin Lights" switch powers the circuit and baggage light has its own switch after that. I always figured if the light wasn't bright enough, because it is small, I could always add another (or 2, etc.) but it's adequate.
 

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Is that panel made to fit under the roll bar brace? My roll bar brace has no holes for a cover plate and I don?t have one in my parts set. Did you make that yourself?
 
You are correct - I forgot that I fabricated that panel (and added nut plates for attachment). It was relatively easy before installation of the roll bar brace, but would be doable afterwards.
 
Hello JDA_BTR,

You are correct that the GAD 27 has 3 DC reference voltage backlight buses to control devices like the GDU 4XX displays and GTN 6XX/7XX as well as 3 PWM drivers to power devices like LED strip lights (500 mA max).

You can control your GDU displays and the GTN from the same DC lighting bus, but since you have multiple, it is probably better to use them. Note that even if you use all 6 lighting buses, you can control them from a single 10K potentiometer if you like.
Steve/g3xpert,

Is 10k a hard requirement for the pot value? I'm looking at using dual concentric pots for my dimmers and the only ones I can find come in much higher values, like 100k or 250k.

Thanks!

Dave
 
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Another decent place for a light in the baggage area is on the back of the flap motor bracket. Or on the side. Or on the aft bulkhead panel with a disconnect for when it needs to be removed. Or perhaps best just on the upper part of the aft cabin bulkhead. I built my own main fuse harness but I included some of the unused wires; this would be a good application for one of them.
 
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Yes.
One end of the pot to 12 volt power (fused or CB); other end to ground; middle ?slider? to GTN(s).

So we are about to connect all this up and get some electrons flowing.

Can I connect one end of the pot to power, the other to ground, and the middle to 3 GDU displays? Will splicing the wires onto the middle post cause any issues?

I can't tell from the discussion / from the G3X manual (which states "For providing this reference signal to more than one device, a commercially available regulated backlight voltage reference is recommended.") . My assumption is that by "more than one device" they mean differing devices, not 3 similar displays...

Thanks in advance.
 
As Walt said earlier, you can control all three displays from the one pot. If you?re concerned, or want to tie into even more stuff, you can use the pot to control an LM317 type voltage source ($2).
 
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