SV-KNOB-DIMMER Questions

[cbretana]

I cannot see my screen at night as it is too dim. I need to use an external dimmer as described in installation manual on pgs .

But I have a Rutan Long EZ, with very limited panel space, so first question is how big is the SV-KNOB-DIMMER? Is it the same size as the other panels, like intercom, transceiver, or Autopilot panels? Please provide the dimensions. (The space in upper right is planned for the Heading/Altitude/Baro panel). If it is as large as the other panels, can the knob and associated electronics be separated from the rectangular fa estate and installed by ursekf Ina smaller hole in my panel?

Second question is: I have been following other threads in this forum about the dimming issues and the use of this panel. The last I read from Don Jones is that the HDX still uses the internal sensor, even when set to EXTERNAL, and has a hardware issue with backlight bleeding into the sensor, that requires a hardware fix. Is this still the case ? Will I gave to get an RMA and send my panel back to you guys to use the Dimmer Knob panel?

 

[GKC Aviation]

The dimensions are on page 15-25 of the install manual

I'm sure you only need to use the dimmer panel with the SE, for a HDX you can make your own out of a suitable potentiometer of your choice.

 

[Rhino]

You should use a separate potentiometer rather than the knob panel, because it takes up much less space. It is my understanding the issue with bleed over from the backlight is not serial number specific. It's just luck of the draw. It also appears to affect both single and dual screen installations, but I'm not 100% sure of that. So you may not know if you need a hardware fix until you actually install a potentiometer.

 

[cbretana]

Rhino,

In the Installation manual, on page 4-39, it says "The brightness level of SkyView and Dynon Avionics panel units can be increased or decreased by applying 0 to 36 volts DC to a SkyView display’s DIM INPUT (Pin 25)".

on pg 15-29, it says that the SV-KNOB-DIMMER violet wire should be connected to Pin 25 of Skyview display. Just below that it says that
"To set the backlight level so that it is controlled by an external variable voltage input (0-30V DC), set BRIGHTNESS SOURCE to EXTERNAL. "

Assuming that the SV-KNOB-DIMMER is using the analog approach on Pin 25, (not the PWM approach on pin 26 ) and generating a voltage between 0 and 36 V as described above, how do I get a potentiometer to control and output a voltage of 0-36 V DC ? Would I need to route the 12-14 volts from my aircraft bus through a transformer that jacks it up to 30/36V and then feed that through the potentiometer?
The output of this potentiometer would then be connected to pin 25?

 

[Rhino]

Pin 25 doesn't require 36 volts. That entry in the manual just means it's capable of using up to 36 volts if necessary. You're only going to use system power, 12 volts in your case. This function will not involve pin 26 in any way. Pin 26 is only used to dim certain other lights (slaved) with a non-analog signal whenever you dim the Skyview. Your only concerns in this instance are system power into the potentiometer (12 volts), usually from pin 1 or 20, ground, and the output to pin 25 from the potentiometer. You tell the Skyview to set the BRIGHTNESS SOURCE to EXTERNAL, which tells it to use the voltage coming in on pin 25 to determine the desired brightness level instead of using a light sensor. Then you set EXTERNAL BRIGHTNESS VOLTAGE to 12 volts (that's how it knows what voltage range to look for) and adjust %BRIGHTNESS VOLTAGE to your preferred levels. In the interest of full disclosure, I've never personally done this on a Skyview system. I've only had it explained to me. So I defer to (and welcome) the experience of anyone who has done this before.

 

[cbretana]

Rhino,
Thanks so much. Now it all makes sense. The EXTERNAL BRIGHTNESS VOLTAGE and MINIMUM BRIGHTNESS VOLTAGE settings tell the HDX display what range of voltages will be input on pin 25, representing the desired range of brightnesses.
This allows the use of an external potentiometer in aircraft with either 14 or 28 volt electrical bases.

My only real complaint with Dynon is the lack of clarity of their documentation. Some of it is due to attempting to combine information for both the HDX and older systems into a single document, but in many cases it is just ambiguous and/or unclear.

 

[GKC Aviation]

Just out of interest, have you tried modifying the automatic dimming via the setup pages?
You should be able to set the minimum brightness there.

 

[cbretana]

Just out of interest, have you tried modifying the automatic dimming via the setup pages?
You should be able to set the minimum brightness there.

Not yet, and I have not tried using the Offset Dim page in the menu either. I know about them and would use them, but at night, I want to have the capability to tweak it with a knob inflight without going through a menu.

 

[tniel7331]

I have used it, but if you try multiple components, like other radio backlighting together its very choppy. For the Dynon display alone it works as advertised, but I prefer the auto mode personally

 

[Rhino]

You should never hook any other lighting to the pot on pin 25. Dynon uses a voltage step process for dimming that may not work properly with other lighting, which could explain the choppy response. It could also potentially cause damage. If you want to use the same knob to dim other lights in addition to the Skyview, you should use a multi gang potentiometer that isolates the signals from each other. Or you could use pin 26 to dim other lighting in conjunction with the Skyview, which is what that pin is designed for. Be aware that in both instances though, you may not get the exact same dimming effect on different lighting.

 

[cbretana]

Pin 25 doesn't require 36 volts. That entry in the manual just means it's capable of using up to 36 volts if necessary. You're only going to use system power, 12 volts in your case. This function will not involve pin 26 in any way. Pin 26 is only used to dim certain other lights (slaved) with a non-analog signal whenever you dim the Skyview. Your only concerns in this instance are system power into the potentiometer (12 volts), usually from pin 1 or 20, ground, and the output to pin 25 from the potentiometer. You tell the Skyview to set the BRIGHTNESS SOURCE to EXTERNAL, which tells it to use the voltage coming in on pin 25 to determine the desired brightness level instead of using a light sensor. Then you set EXTERNAL BRIGHTNESS VOLTAGE to 12 volts (that's how it knows what voltage range to look for) and adjust %BRIGHTNESS VOLTAGE to your preferred levels. In the interest of full disclosure, I've never personally done this on a Skyview system. I've only had it explained to me. So I defer to (and welcome) the experience of anyone who has done this before.

Rhino,
I'm getting a pot to use for this, but they come in a variety of maximum resistances, from 100 ohms up to 100k ohms. What size should I use?
Assuming that when the pot is all the way counter-clockwise, it is at 0 ohms and will output 12 volts, I would imagine that as you turn it clockwise, at some point it will reach a high enough resistance that the output voltage will go to near zero. Isn't it important to use a pot that has a maximum resistance such that it will not reach zero voltage until you have turned it through a significant portion of its full arc? What resistance would accomplish that?

 

[Rhino]

Your biggest concern is making sure the pot is capable of the amperage you're putting through it. Without exact specs from Dynon, I'd probably start with 10k.

Looking at the SV-DIMMER in the install manual, I'd be willing to at least guess the knob can be removed from the bezel. Then you could simply install the knob directly into your panel, which might solve your problem. I'd ask Dynon if that's possible before trying to engineer something else. Or maybe someone else here who has one can chime in.

 

[cbretana]

Yes, I will try the 10K one first, it's only $10 from Amazon. Dynon Tech support is shut down for the holidays until early January. Thanks for your help!

- and Happy New Year!

 

[Rhino]

10k should give you about .0013 amps and .017 watts. Should work if all you're dimming is the Skyview display. If you want something more than that, I suggest you contact someone like vlittle. Vern knows more about the engineering stuff than I do.

 

[cbretana]

Thanks! Yes, all I am doing is dimming the Skyview HDX display. I have very limited panel space, and the SV-KNOB-DIMMER is too large to fit anywhere. And, at just $10, the potentiometer from Amazon sure beats the price of the SV-KNOB-DIMMER from Dynon ($90).

 

[Rhino]

Not part of what cbretana is doing right now, but to provide a future reference for others that might want to dim other lights such as panel lights or switch backlighting, the above mentioned PWM output from pin 26 will dim other LED lights in conjunction with the Skyview (slaved). There are certain considerations and limitations to keep in mind that are addressed in the Skyview Installation Guide and the Third-Party Connection Guide for that.

However, if you want to dim other LED lights independently (non-slaved) without using pin 26 on the Skyview, a standard potentiometer will not work correctly if your lights are looking for a PWM input. You'll need something designed specifically for that, such as this dimmer;

https://smile.amazon.com/Oznium-Dimmer-Rotary-Control-Switch/dp/B085TK13SH

Depending on what LEDs you use, it still may not work correctly when dimmed. Some LEDs have a constant current driver that puts limitations on the frequency of PWM signals, and the lights flicker as a result. It's usually better to get the lights and dimmer from the same source, to have the best chance of compatibility. For instance, the manufacturer of the dimmer above also sells LEDs. No, I'm not endorsing them. I've never bought from them. Just using them as an example.

 

[Rhino]

By the way, let us know how things turn out. The things we all learn here, both good and bad, serve as a reference for other folks who come here looking for answers later.

 

[cbretana]

Okay it's done, and it works. But I am left with some questions.

First of all, I learned what a potentiometer is, and why they have three leads, instead of just two like a rheostat. A potentiometer has three leads because it's just really two rheostats in one. Where a rheostat has an input lead, that is connected to the sliding contact that moves back and forth across the resistor, and an output lead attached to the end of the resistor,, the potentiometer has an input attached to the sliding contact like a rheostat, and two output leads, each of which is attached to opposite ends of the resistor. In this way, the potentiometer is actually a voltage splitter.

But if you only use one of the output leads, it is effectively just a rheostat. So in adding this capability to your panel, you can use a single rheostat, or just two of the three leads on a potentiometer. You need to attach one wire to the input lead, (that is attached to the sliding contact inside the potentiometer), and the other wire to one of the output leads. Which lead you connect the other wire to determines whether the voltage increases when you spin the knob clockwise, or the other way around. On the other end, one wire goes to 12volt aircraft power, (I attached it to the 5 amp HDX CB, and the other wire goes to pin 25 on the Skyview DB-37 harness. As wired, once the brightness settings are set as described in install manual, it all works as advertised.

This is the Potentiometer I am using:
Heyiarbeit 10K Ohm Carbon Film Potentiometer 18mm Long Handle Variable Resistors Single Turn Rotary

That left me wondering, what exactly are the three wires attached to the SV-DIMMER-PANEL for? Is whatever is inside the DIMMER-PANEL a potentiometer, or just a Rheostat? And why does the wiring diagram for the DIMMER-PANEL call for one of the wires to be attached to ground? What's up with that?

 

[Rhino]

A rheostat works in series. A potentiometer works in parallel. You can get the same voltage off each, but they don't drop the same current. Using just two leads, or using a rheostat, you're putting the entire current of that circuit through your load rather than just picking up a control voltage. That can be dangerous to some components, and that may well be true here. I've worked in electronics for many years, but I'm no engineer. However, if an engineer designs in a potentiometer, I assume there's a reason for it and I respect that choice. I'm not going to claim what you're doing is dangerous, but I would not take that chance. It's your plane, but I advise you to use the potentiometer as designed.

By the way, glad it's working.

 

[Rhino]

As for your other questions, there's a potentiometer in the dimmer as far as I know. That would of course explain the three wires. The resistive component in the potentiometer drops the entire voltage across it from 12 volts to ground, hence the ground lead. The lead picking up the variable voltage up off of that is the third wire. Envision a resistive metal strip. 12 volts goes in one end and ground is on the other. Across the length of that metal strip, the inherent resistance of the strip gradually drops the entire 12 volts. If you touch a meter to the center of the strip, you read six volts. If you touch the meter a third of the way across the strip, you get four volts, etc., etc. The third wire on a potentiometer is essentially the same as the meter lead. As you rotate the knob, the pickup lead on that wire moves back and forth along the strip and gives you a changing voltage depending on where it is at any given time. That goes to your load, the lights in this case. The difference is, what comes off the pickup lead to the load does not drop the full current of the circuit, except when the potentiometer is turned fully on. Using only two wires, you take the strip completely out of the equation. Your load always carries the full amperage of that circuit, no matter the voltage level. The component life will be reduced at the very least.

That's an overly simplistic explanation of course, but it gives the general idea.