dome light dimmer (with delay)

**kronos** · 11-01-2005, 07:19 PM

Intro & disclaimer
For all you guys out there that want a fading dome light (aka courtesy light aka theatre lighting) without having to pay for one, you can build your own. I have attached the schematics and you can build it for a few bucks given that you don't have any spare components lying around otherwise it can cost you absolutely nothing. Of course you can rip some parts from your TV, CD player, radio, etc., but I'm not responsible for the damage you cause this way

The way it works
I won't bother you with technical details, but if someone is interested just let me know and I'll explain in detail. For now just the basics. There are two stages: first one is delaying and the second one is fading. When you open the door the light turns on. You get inside and close the door, but the light stays on (delay stage) for an adjustable period of time (0-40 sec. for the values in the scheme, but you can easily modify that i.e. put a bigger capacitor) so you can see where to insert the key or do whatever you do when you get in the car, then fades away (fading stage) with an adjustable speed. If you connect the ACC wire (which is entirely optional) when you turn the key to ACC position the light turns off (actually fades) even if the delaying stage is not over (it cancels the delay stage).

Setup
The SR1 trimmer pot adjusts the delaying time (the period that the bulb is at full intensity) and you have a "witness" LED that is lit during the delaying stage; that way you can set it visually to whatever duration you like. When the first stage ends (marked by the LED not being lit anymore) enters the second stage - fading. The SR2 trimmer pot adjusts the fading time (or speed if you prefer)

The first image depicts how the dome light switch is usually connected (depending on the make and model of your car the connection may be different in which case you'll have to figure it out).
The second - the schematic and the connections to the dome light switch.
The third (and last) is an actual image of the finished product made on a PC board (you can get those from radio shack or your local electronics store)
Hope someone will find this useful.

**Cris** · 11-01-2005, 07:46 PM

This is sweet! I already have that feature on the car, but I wanted to add some more lights in the car, so this is usefull! Thanks, I think I'll give it a try!
Can you post a pic of the back of the finished board?

**kronos** · 11-01-2005, 09:09 PM

Here ya go. My hand was a little shaky, but since it's not a pcb I'm afraid it's not looking nice at all anway.

**Peoples** · 11-01-2005, 09:22 PM

i saw someone selling these things a while back for like $25.....but i'd rather build it
i finally feel like doing a project like this now...thanks!

**mauri** · 11-02-2005, 04:19 AM

To do this its very more simple to use a common NE555....

Mauri

**lez** · 11-02-2005, 05:12 AM

but they dont fade...........

**lez** · 11-02-2005, 05:13 AM

can you not connect acc line via diode (4148) to pin 2 save on a resistor and a transistor?

Can the value of r1 be increased it looks a little low to me, passing 12v from acc to gnd

**kronos** · 11-02-2005, 07:47 AM

@lez
yeah you can use just a diode, but there's a downside to it: you'll have to increase the value of r1 indeed, but this will affect the c1 discharging time (which I tried to keep to a minimum for a quicker response) hence the transistor. of course you can increase r2. anyway for me it's working just fine; I'm testing it continuously over the past 5 days and so far no problems, I don't even use a radiator on the 3055.

@mauri
I was just trying to give something that may prove useful to some of the folks here. if you feel that this particular design is flawed then help improving it or just make a better one; there's no use in saying that it could be done otherwise, cause it's already done. no offense intended.

**ethlar** · 11-04-2005, 10:32 AM

ive ordered the parts and am building this for my car, its the little things that make me happy, thanks for posting this

**PatO** · 11-04-2005, 11:27 PM

Kronos - how many bulbs are you lighting up? I have 4 lamps on that circuit (2 domes & 2 floor lamps) and was wondering if the transistor would require a heatsink. (not that big of a deal, but since Rat Shack is closed right now, all I can do is dream...)

Thanks for circuit!!!

BTW - what software did you use to create the diagram? I see diagrams like that all over the place...