ATTN elec. Gurus, lighting/dimming question

[OCD]

Yea i went and bought a tube of epoxy for this time. Ill have to see if this time I can get it done right haha.

Thanks
Dan

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[OCD]

Aright well i tried it again and guess what, two resistors burned up almost immediately. They burned up on the neg input side. The resistor's crossing the op amp burned up almost immediately while the resistor on the neg illum didn't burn up. The fourth resistor started to burn but not as quickly as the others (connects the 3 and 4 with the ground). I just not sure what I could be doing wrong. The guage does work for the short time before it burns up. I am thinking could it possible be that i am connecting the + and - illum backwards. I am using the orange wire as the - and the violet as the +. Any suggestions.

Thanks
Dan

[vrg3]

Mixing up the two illumination wires shouldn't cause this kind of problem.

This doesn't make any sense. You shouldn't be able to use a car's electrical system to force enough current through a 10K resistor to burn it up. Dumb question -- you are using 10 kiloohm resistors, right, not 10 ohm resistors or something?

[OCD]

WOW, i def am using regular 10 ohm, I feel like an idiot right now. I will go and pick up the 10k ohm resistors and try it again. Thanks a million.

Dan

[vrg3]

Heh, that'll do it . Good luck.

[OCD]

Yea it works now, thanks again I really appreciate it.

Dan

[djerickd]

I just built this tonight, is there a limit to how many guages can run of of it?

[yosemitemtb]

I made one of these today, it works great! Thanks for posting this. $3.85 for parts and only a couple of burns from the soldering iron, well worth the effort.

[djerickd]

I've made one but I still need to hook it up

[djerickd]

I finally did this with my 2 Omori guages, and it works great!! thanks for the idea and the write-up! I love little cheap and easy mods like this

[reasonable rock]

is anyone still watching this thread? i built three of these and can't seem to get it right. can anyone help? i believe i am using the correct parts, i am not overheating the contacts... anyone?

[yosemitemtb]

Originally Posted by reasonable rock

is anyone still watching this thread? i built three of these and can't seem to get it right. can anyone help? i believe i am using the correct parts, i am not overheating the contacts... anyone?

I guess the first thing is to make sure you are using 10k ohm resistors as in 10,000 ohms.

[QueensEng]

Digging this up from the dead...

Prosports have the same issue with a shared ground between the gauge power and LEDs, and I desperately want to be able to dim mine for night-time driving.

As I understand it, the two 10k Ohm resistors bridging pins 2/8 and 3/7 are for voltage splitting only, so irrespective of the current draw from the LEDs (as I'm sure they differ from those in the Omori gauge) this circuit will achieve the same result.

Can anyone confirm this?

[Vlad]

I can confirm that the dimmer for Omori dimms the DepoRacing gauges with no problem. The Depo look identical with the Prosport, so give the Omori dimmer a shot.
I am currently dimming one omori and 3 depo gauges off of one dimmer and it has worked for the last year.
The Depo gauges I have added a rheostat for each one, so I can match intensity for all of them.

[QueensEng]

Originally Posted by Vlad

I can confirm that the dimmer for Omori dimms the DepoRacing gauges with no problem. The Depo look identical with the Prosport, so give the Omori dimmer a shot.
I am currently dimming one omori and 3 depo gauges off of one dimmer and it has worked for the last year.
The Depo gauges I have added a rheostat for each one, so I can match intensity for all of them.

Excellent, very much appreciated.

I'll document and post the result. Frankly, I'm surprised no one has tried it before given the ubiquity of the Prosport gauges in the community and the amount of posts I filtered through asking this question without an answer.

[SVXdc]

Starting in 2008 (same year Subaru changed to the new 20-pin harness for the radio's power and speakers), Subaru switched to LEDs for the instrument illumination. LEDs do not dim well by simply varying the voltage. So the car's dimmer circuit was changed to a pulse-width modulated (PWM) signal -- +12V switched rapidly "on" and "off". This is the proper way to dim LEDs. The car's dimmer wheel adjusts the percentage of the LEDs' "on" time (the "duty cycle"). It happens so fast that the LEDs simply appear dimmer or brighter.

As in older years, the car's illumination(+) signal is simply +12V when you turn your headlights switch to either the parking lights or headlights position.

The car's illumination(-) lead is the PWM signal (a square wave, alternating 0 and +12V). Frequency is 250 Hz. Note that since this is the "negative" (low) side for the LEDs, brightest illumination happens when the PWM signal spends most of its time at 0 Volts. For dimmest lights, the PWM wave spends most of its time at +12V.

So if you can separate both sides of your gauge's LED, you can connect it across the car's illumination(+) and (-) leads and have it dim in tandem with your other instruments. You may still need a series resistor to limit the current through the LED.

If you can't or don't want to split off the gauge LED's ground lead, you might still be able to connect the LED's positive lead to the car's illumination(-) signal. You would need to invert the car's PWM signal (so that you end up with a signal with higher % time at +12V means "brighter"). It would be easy to do that with a simple transistor circuit. As a bonus, you can use the illumination(+) signal (or even +12V Ignition) for your circuit's +12V supply to the LED(s), and then you won't have to worry about possibly drawing too much power from the car's illumination(-) circuit.

Check with your gauge's manufacturer to make sure they don't already have some funky internal dimming circuitry that won't like being fed a PWM signal. If they just have a straight LED (or even incandescent bulb), there shouldn't be any problem.

[Cougar4]

Thanks for the info about the new illumination circuit design SVXdc. That is good to know about.

[QueensEng]

Originally Posted by SVXdc

Starting in 2008 (same year Subaru changed to the new 20-pin harness for the...

Copy that, I now see earlier in the thread they're talking about strictly varying the illumination(-) from 0-12VDC. I always knew our systems was PWM, I just didn't know it wasn't always.

So it looks like I'm going to have to split open the gauge, cleave the LED grounds from one another and bring them to the 20-pin radio harness on their own. Doable, if, like you said, there isn't any bizarre circuitry.

Gauges arrive next week, I'll post a DIY if I decide to go for it.

Thanks for the insight SVXdc.

[QueensEng]

Originally Posted by SVXdc

Starting in 2008 (same year Subaru changed to the new 20-pin harness...

I've spent the weekend mulling this over and I'm leaning towards leaving the gauges intact, not separating the LED and gauge ground leads. You mention using a transistor circuit, could you not achieve the same result using an op amp with gain -1 to invert the car's illumination (-) signal?

You could power the LM741 across ground/Illumination (+), use a pair of 10k ohm resistors to get a gain of -1, and your output at pin 6 should be the inverse of the illumination (-) input at pin 2.

Correct me if I'm wrong, and if I'm way off base, could you give me more details on the transistor circuit you mentioned?

- DR.

[SVXdc]

An OP amp circuit would probably work too, but I'm sure that a transistor circuit would be simpler and cheaper.

Here's the first one I found via Google.

[Soarer]

Praise to the Electrical Gurus! Reviving this thread to ask some questions for a build I'm finishing up.

2005 Legacy GT Ltd. Wagon... Installing AEM 30-4100 EUGO wideband, Auto Meter 3646 Sport-Comp II pyrometer & Auto Meter 3603 Sport-Comp II boost gauges. Want them to dim with my dash dimmer switch.

Will one of these fancy-schmancy electrical converter joints work for my setup? Do I need to change anything around or do it just as described? Thanks much for any help you gentlemen can provide.

[Cougar4]

If the gauge lighting is LED and isolated from ground then I think you can tie the wires directly across one of the other lights, like for the clock. The main thing you have to be careful of is the total current draw for the new lights and they don't connect directly to ground.

[SVXdc]

Although Legacys/Outbacks switched to LEDs slightly earlier than Imprezas & Foresters, I 'm fairly sure that 2005 Legacy/Outback was still using incandescent bulbs and the old-style variable analog voltage for dimming. I think 2006 Legacy/Outback is where Subaru changed. 2007-up Legacy/Outback are definitely PWM.

If your gauge (or whatever accessory) has LEDs that you want to dim, things are a bit trickier in older cars with analog dimming.

Here are all of the permutations:

1. Newer car with PWM dimming on the illum(-) lead
   1. You are able to split off both sides of gauge's illumination LED/bulb (so neither side of LED/bulb is tied to gauge's ground lead)
      1. Gauge uses LED
         • Simply connect LED across car's illum(+) and illum(-) signals
      2. Gauge uses incandescent bulb
         • Simply connect bulb across car's illum(+) and illum(-) signals
   2. You are unable to split off both sides of gauge's illumination LED/bulb (so one side of LED/bulb is tied to gauge's common ground lead)
      1. Gauge uses LED
         • Use transistor inverter circuit that I described in my earlier post
      2. Gauge uses incandescent bulb
         • Use transistor inverter circuit that I described in my earlier post
   .
2. Older car with analog (variable voltage) dimming on the illum(-) lead
   1. You are able to split off both sides of gauge's illumination LED/bulb (so neither side of LED/bulb is tied to gauge's ground lead)
      1. Gauge uses LED
         • Although you could connect an LED across car's illum(+) and illum(-), it probably won't dim quite the same as your car's other backlights and instruments, and may fade to 'off' before the others do.
           Ideally you would want to add an analog-to-PWM converter circuit for the LED
           [don't ask me for a circuit -- I'll let some one else do the research and post here. There may be pre-built modules on eBay].
      2. Gauge uses incandescent bulb
         • Simply connect bulb across car's illum(+) and illum(-) signals
   2. You are unable to split off both sides of gauge's illumination LED/bulb (so one side of LED/bulb is tied to gauge's common ground lead)
      1. Gauge uses LED
         • You'll need to either add an analog voltage inverter (as vrg3 and skivvie discuss earlier in this thread, and vrg3 posted here), with the limitations I mention above about LEDs not dimming well from a variable analog voltage; or add an analog-to-PWM converter circuit
      2. Gauge uses incandescent bulb
         • Add an analog voltage inverter (as vrg3 and skivvie discuss earlier in this thread)

In all cases with an LED, make sure you have a current limiting resistor in series. A gauge with an LED should already have one (but you would need to make sure you don't lose it if you separate the LED from the gauge's common ground). Some LEDs have one built-in (internal).

[JonnyWachter]

Aalright, so i'm reviving this thread. I built the transistor, hooked it up and the illumination is still reversed. I can completely bypass the unit and plug my illumination wire into the black/white wire and get the same result... what is going on here? Car is a 2010 STI.

[Cougar4]

I'm not sure what you mean by 'reversed'. I assume you already know that the illumination control is done via the return side of the power supply to the lights.