pwm dimmer questions and how to select right one

[E415Z]

Hello new member here trying to see if the good folks here can help me out.

Wound up doing a climate control conversion on my Chevrolet Impala from a Buick Roadmaster. The rest of the climate control works fine(lights up and dims with rotation of interior switch) but digital part of the climate control stay bright. The Roadmaster wiring tapped into the factory radio to obtain a "VF-PWM signal from radio to dim Flourescent Display" on the climate control but I don't have the factory Roadmaster radio.

Ive spoke with a few people who have done this conversion and they take the factory radio and wire it in their car somewhere(usually trunk) but I feel that their has to be some other option.

And here is where I'm at. I've been on eBay looking at PWM dimmer controllers but I am unsure of which one suits my needs best. Correct me if I'm wrong, but wouldn't I need positive 12v ,negative, illumination for input(lights) and the pwm wire would be the output? Should I get a multimeter and see what is being put out by that wire? what should I test for?

Thanks

 

[Arouse1973]

Hello
Just interested in why the radio controls the brightness of the display? Is this when it's dark and you have your lights on? Is that what you mean about input lights?
Cheers
Adam

 

[Gryd3]

Hello
Just interested in why the radio controls the brightness of the display? Is this when it's dark and you have your lights on? Is that what you mean about input lights?
Cheers
Adam

I've seen a number of new vehicles pass of responsibility of functions to the stereo...
From the sounds of it, the analogue lighting components dim properly, but with the stock stereo removed, the digital displays don't dim any longer. It may be as simple as adding a voltage controlled PWM source to the vehicle.
Service manuals and wiring diagrams will help. So will exact model numbers (or as close as you have)

 

[Arouse1973]

Yes I think your right. Some people have stripped the stereo apart and just used the required components for the PWM. I get a bit nervous when people mention about modifying vehicle wiring.
Adam

 

[Gryd3]

Yes I think your right. Some people have stripped the stereo apart and just used the required components for the PWM. I get a bit nervous when people mention about modifying vehicle wiring.
Adam

Agreed. These types of topics are usually locked, but the only modification is to the lighting behavior of the climate control digital display which should not impact emergency services or other important functions.
This topic may continue if this continues to be looked at more like an automotive sound system modification, and the op shows a good understanding of what (s)he is working with.

 

[Gryd3]

Correct me if I'm wrong, but wouldn't I need positive 12v ,negative, illumination for input(lights) and the pwm wire would be the output? Should I get a multimeter and see what is being put out by that wire? what should I test for?

Thanks

I should have commented on this sooner.
A PWM controller (3rd part or home-made) will most likely need Ground, Power (12V or other), Illumination (This could be an analogue input, or a simple on/off input), and a PWM signal output.

We can't specify what you need without some more info on the vehicle or original head-unit. Measurements on the Illumination wire would be required.
The PWM wire being disconnected and showing full brightness makes it seem like a logic input, but the logic level could be anywhere from a couple volts to 12V, and it would be helpful to measure what that wire is as well currently. (It may have a pullup resistor)

Do you have any contacts that could get measurements from a working model?

 

[E415Z]

I should have commented on this sooner.
A PWM controller (3rd part or home-made) will most likely need Ground, Power (12V or other), Illumination (This could be an analogue input, or a simple on/off input), and a PWM signal output.

We can't specify what you need without some more info on the vehicle or original head-unit. Measurements on the Illumination wire would be required.
The PWM wire being disconnected and showing full brightness makes it seem like a logic input, but the logic level could be anywhere from a couple volts to 12V, and it would be helpful to measure what that wire is as well currently. (It may have a pullup resistor)

Do you have any contacts that could get measurements from a working model?

Thank you to all so far.

Yes, only the dimming part of the display is affected and it stays at full brightness at all times.

Original head unit is from a 1996 Buick Roadmaster and it was swapped into a 1996 Impala SS.
I do that GM used the same idea of basing dimming off the pwm signal because the roadmaster radio is in several other vehicles and years.
I will get Measurements soon

 

[E415Z]

Measured the wire and I got .05 on the readout.
Does that even sound correct? I think I'm more confused now. I assumed that this wire didn't have any power from it because It would obtain it from the PWM controller.

 

[Chill]

Hello new member here trying to see if the good folks here can help me out.

Wound up doing a climate control conversion on my Chevrolet Impala from a Buick Roadmaster. The rest of the climate control works fine(lights up and dims with rotation of interior switch) but digital part of the climate control stay bright. The Roadmaster wiring tapped into the factory radio to obtain a "VF-PWM signal from radio to dim Flourescent Display" on the climate control but I don't have the factory Roadmaster radio.

Ive spoke with a few people who have done this conversion and they take the factory radio and wire it in their car somewhere(usually trunk) but I feel that their has to be some other option.

And here is where I'm at. I've been on eBay looking at PWM dimmer controllers but I am unsure of which one suits my needs best. Correct me if I'm wrong, but wouldn't I need positive 12v ,negative, illumination for input(lights) and the pwm wire would be the output? Should I get a multimeter and see what is being put out by that wire? what should I test for?

Thanks

Hey I was wondering if you ever found a solution to your issue. I have a 1995 Buick Roadmaster and I purchased it with an aftermarket radio. I had an old radio from another Roadmaster, so I gutted that thing and used the main board to enable the dimming the the A/C control unit's Vacuum Fluorescent Display; works great. As a B-Body owner, you should know there is quite enough room in the dash to shove that thing into.
Looks something like this:
http://chillrobb.com/roadmaster/F/PWM2.jpg

I purchased a chip from China, looks exactly like this:
http://chillrobb.com/roadmaster/F/sm_MODULE.jpg

You can certainly see a difference in dimensions. So this module converts voltage to a PWM signal. 0-10 volts is converted to 0-100 percent duty cycle PWM, respectively, from the vehicle's dimmer knob.

I wired this thing up and it worked great, with one exception. The result was something like the opposite of what I wanted. I was excited because it worked at all, the problem was that when I adjusted to low dim the display got brighter, and when I turned the knob for high brightness, the A/C display got dim. Maybe someday, but right now I am not qualified as an electrical engineer, but my research on just what Pulse Width Modulation is had led me to learn that there is something like an inverted signal. I know Calculus, and graphs of these digital signals are pretty easy to grasp mentally, and the inverted signal is just what it says, instead of on it's off. I was wondering if maybe since I needed the opposite effect, maybe I need something to convert voltage to an inverted PWM signal, that would be so simple.

So now we are at the point where, like my friend says, "WHY?!?!" I start to wonder myself, but that can be saved for another discussion, for those that are not aware of what it's like to operate these beautiful machines.

I should have just put that old radio into my car, but I plan on upgrading the sound system later anyways. And I don't think I plan on putting the radio back together, at least in the correct manner. So I ordered a new chip that has many more jumpers, and adjustable settings, so I can go inverted or not. I certainly can't find anything manufactured anywhere other than China, and shipping sucks. My last idea involves building my own board using the TI-555 chip; apparently that chip is pretty bad ass and can do many things. But my old radio board works, like from the factory, and people already make circuit boards for this, and I really don't now enough about what I'm doing. But somehow I'm on the right track, and I don't know know of anyone who has ever taken this issue beyond the common solution of wiring an old radio.

So that's it, I think I am going to label this as a "Rant".

 

[Bluejets]

Read someone had similar and by applying full 12v the display would extinguish so I'm guessing something to sink the signal wire.

 

[Chill]

Read someone had similar and by applying full 12v the display would extinguish so I'm guessing something to sink the signal wire.

The dim signal is a voltage, the input for the A/C control unit VF display needs to be a PWM signal. If you apply any voltage to this input wire the VFD goes completely blank. What is needed is something to convert the signal from DC voltage to the correct type of PWM signal. What I tried apparently was the wrong kind of PWM signal, but it still worked, just not how I wanted, so there's got to be something there I'm doing right.