Installing an LED Dimmer for Instrument Panel Illumination - Rheostat Replacement

[DrJeff]

When you replace the incandescent bulbs in the instrument panel (binnacle) with LEDs, you unfortunately loose the ability to dim the lighting with the stock rheostat. I wanted to have the ability to dim the LEDs so I worked on this project to replace the stock rheostat with a PWM (Pulse Width Modulator). The PWM dimmer currently costs $15 from SuperBrightLEDs.com (I think I paid $20).

This project is not 100% completed (too many other concurrent projects holding it up - so probably 90% complete), but I've written up what I've done so far. I'd certainly appreciate any feedback from the forum - especially before I close everything back up again!

Installing an LED Dimmer for Instrument Panel Illumination.pdf

When I get the other projects completed I'll update this document and post some pictures/videos of the LED dimming in action.

[Bitsyncmaster]

Nice write up. I saw super bright was selling a bunch of those PWM type dimmers. I don't know why they would need to run wires to both sides of the LED. Wonder if all their units work that way.

[Ozzie]

Nice!

Neat project, Jeff. At DCS 2012, Josh said that another owner had also made some mod to dim the LED dash lights and I emailed and PM-ed him to get more details to put on my "100% LED light" blog, but never got a response.

Glad to see that you've done something similar, and documented it (very well, I may add).

[DrJeff]

Nice write up. I saw super bright was selling a bunch of those PWM type dimmers. I don't know why they would need to run wires to both sides of the LED. Wonder if all their units work that way.

If you could just pick up a returning ground from the binnacle, it would be a lot easier. I'm curious if they are always shown with a dedicated ground because of the effect of the PWM waveform on other components using the same ground? It would be interesting to test this, but I'd need to be looking for the possible side effects on other binnacle devices or possibly other things connected into the same ground. I've avoided the problem (if there is one) by wiring in the dedicated ground - but it would be a very simple project if this could be avoided.

[DrJeff]

I just spotted the same PWM dimmer unit on Amazon.com for $7...

http://www.amazon.com/LEDwholesalers...=pd_sbs_auto_1

[Chris4099]

Amazon now has it down to 20 cents (plus $5 shipping), so I ordered one. Once it arrives, I'll take a closer look at it. For all we know, they have that separate negative out to keep wiring simple for most people (simply wire the dimmer in-line with most household LED systems). With some luck, both negatives are simply connected together internally and there would be no need for a dedicated ground.

[DrJeff]

...With some luck, both negatives are simply connected together internally and there would be no need for a dedicated ground.

It is certainly worth testing connecting the PWM to the grounds available in the driver's footwell (where undoubtedly the binnacle's grounds connect). My dash is disassembled at the moment and I can't run the test. I'd be very interested to hear about your results.

About the only thing that sounds suspect with the plan is that the PWM has two ground connections, one paired with the +12v input and one paired with the +12v line running to the LEDs. This test would suggest that both grounds could be connected to the same ground point. It seems to make sense - but why wouldn't the PWM designer just have a single ground connection, instead of two grounds?

[DrJeff]

Just a heads-up that this project uses LED bulbs I got about 6 months ago. In another thread on this forum they've been discussing changes to the components included on SuperBrightLEDs (resistors and capacitors - but on different bulbs from this project) that may make them less compatible with the type of PWM dimmer specified in this write up.

I might have just got lucky with the bulb and PWM being compatible.

[Chris4099]

The PWM dimmer arrived today and I cracked it open. To my surprise, it does the PWM on the ground side, not the positive! So tapping into the negative side of the binnacle wiring is required for this unit. Bummer. The positive connection terminals are the ones connected together and only need one lead.

[Bitsyncmaster]

The PWM dimmer arrived today and I cracked it open. To my surprise, it does the PWM on the ground side, not the positive! So tapping into the negative side of the binnacle wiring is required for this unit. Bummer. The positive connection terminals are the ones connected together and only need one lead.

Driving the ground is so much better. Less electronics and higher reliability but as you said, not as easy to wire up.