Dome light dimmer - Tested circuit

[gr_diver]

If anybody is interested in fitting a dome light dimmer to his/her car I just finished installing this circuit in my Opel, and it works!

dome light dimmer (with delay) - MP3Car.com

It is simple to build, includes an entry delay, and also has the feature that the dome light fades off immediately when you turn the ignition ON. It was the only DIY circuit I could find in the web, that had all 3 functions (entry delay/ fade/ ignition on canceling the delay).

If you decide to build it, pay attention that the schematic does not indicate that pins 4 & 8 of the LM258 should be connected to "GND" and "BATT" respectively.

Initially I had a problem with it, it would work nicely with a LED as a load, but not with a 5 or 10W automotive bulb. I am not an electronic wizard, I can only assemble simple circuits without actually knowing what each part does, but after reading a bit about transistors at

How do Transistors Work

, I realized that resistor R6 at 39KΩ was too much to make the MJE3055 transistor allow enough current through it. So I replaced R6 with a 0-10kΩ potentiometer, and set it just enough to make the bulb light at full brightness. (in fact you will see my posts concerning that problem if you read down the thread at mp3car.com)

It works nice, it's good to have the dome light stay on until I fasten my seatbelt, put the stereo's faceplate on and insert the key to the ignition switch... You can adjust both the entry delay and the duration of the fading to your liking. For me it was 20 seconds entry delay (I timed myself how long it takes to get ready and added 5 secs), and set the fade duration to 3 seconds. The slow fading is also romantic!

[2 Fast 4 U]

Nice piece of work, going to make it for both of my cars, in the winter as a winter project.

[gr_diver]

I found only one downside to this circuit.

If with the ignition on (engine running) you open a door, the dome light will not come on. This happens only if you actually use the "ignition-on delay cancellation". I use it, because I need about 10-15 seconds entry delay the first time I get in the car, and at any small stops afterwards, 10-15 secs would be too long to drive with the light on (at night). But if you decide to have only 3-5 seconds entry delay, you might not use the ignition lead at all, since such short a duration will be tolerable at night, and you will get rid of that small issue.

2 Fast 4 U, if you liked the idea of a dome lamp dimmer, tomorrow check out this thread:

http://www.opelgt.com/forums/general...onics-guy.html

I had some problems with the dome light fader and my alarm (alarm's fault*), and fitted additional dome lights under the dash (above the foot areas), to have the alarm trigger by them. Tomorrow that the whole project will be finished, I will upload a video. I think you will like that as well. Maybe then you can do both as one project...


*The transistorized current fed to the dome light by the fader would not be sensed as voltage drop by my archaic alarm, because it is actually a pretty fast waveform rather than a single voltage drop. So I added a PCB 10A relay to the fader board that triggers when the dome light comes on, and feeds two small lights (5W each) from the "BATT" lead which comes from the fusebox. That current the alarm will sense it and trigger. The small 5W lights illuminate the foot area for both the driver and passenger. I actually did it unwillingly today to the passenger side just to make the alarm trigger, but I liked it so much tomorrow I am doing the driver's side as well!

[gr_diver]

Originally Posted by gr_diver I found only one downside to this circuit. If with the ignition on (engine running) you open a door, the dome light will not come on. This happens only if you actually use the "ignition-on delay cancellation"....

Solution: Put a small PCB relay (12V/10A) on the board, connect it's trigger leads to the ACC and DOOR leads, then connect the T2 emmiter lead (the one with the arrow) to the Common lead of the relay, and then the Normally Closed lead of the relay to pin 2. Thus, when the ignition is on, and you open the door, the connection will open, the capacitor will discharge and the dome light will come on. When you re-close the door, the connection will be closed again, the capacitor will charge instantly through T2 (as intended), the delay will be instantly canceled, and the circuit will go directly to fading.

I did it, I tried it and it works!

Have fun!

[gr_diver]

The mod I described in the previous post seemed to work on the bench, with the circuit fed from a power supply, but in the car there was an issue.

In the car, when the ignition is off, the ignition wiring is grounded. Thus the ACC lead was grounding, keeping the C1 capacitor discharged, and so the dome light was continuously on (infinite entry delay).

A change had to made. A small diode has to be added, between the ACC terminal and the 470Ω resistor, so that the lead cannot ground the circuit. I used a "FR153", and it does the job fine.

Also, it is better to have the relay control the R2 -> T2 connection, essentially in the same way as before (N.C. & C terminals). This way the relay controls the operation of the transistor, instead of disconnecting it's output while it is active.

Now I tested it in the car and works! (Finally)