BMW E36 Blog

This is the third post in the series of how to create a control device to turn your BMW lights on automatically when it gets dark. In the first post Turning Your BMW Lights On Automatically At Night, we’ve seen how it is possible to control a light using an electronic circuit that is sensitive to light. In the second post, Turning Your BMW Lights On Automatically At Night . . . Circuit Diagram, I presented an electronic diagram that can be used as the light controller inside the car. Of course, everything I said until that post was a theory that I’m almost sure that everyone of you thought it’s impossible or at least hard to implement. At least that explains why I didn’t get any comments on that article which I’m pretty sure it’s very interesting to everyone who drives a BMW E36.

Anyway, I decided to go one step further and try to implement my theory and my electronic circuit to see if it’s going to work or not. So, I brought everything that I mentioned in the second post + breadboard to help me implement the circuit and test it to see how efficient it is going to be. After I put the electronic circuit together, I discovered that the relay is not working :p . So, I had to pull one of the car relays to use it in my test. The circuit on the breadboard looked like this (very simply):

After that, I went to the car and connected the wires to my battery and started manipulating the variable resistor until I heard the relay ticking. When I heard the tick I moved the variable resistor back a little bit until I heard the relay tick again (this time it’s disconnecting). Now everything is set up correctly. I tried to cover the CDS (Cadmium Sulfide Cell) with my hand to make it "think" it’s dark and the relay ticked. Yay! it meant that the circuit is really working and all I had to do right now is to connect the car headlights to the relay and we’re done.

The circuit that I used is this:

When I tried to connect the headlights, I left the circuit on and after I connected the headlights to the relay, I tried again and opss. It’s not working anymore. Damn it!

It turned out that my circuit which was missing the 1KΩ resistor that is connected to the transistor base is not going to make the transistor last long. This problem is happening because the transistor base is not supposed to receive high current which I gladly sent to it. To solve this problem, I introduced the resistor to protect the transistor base and replaced the old transistor with a new one. Try again … it worked for a minute and then my radio stopped working 😆

Its seems that my battery went dead because I left the lights on for some time. beginner’s mistake huh 😀

So, I removed the circuit and tried to turn my car on but it didn’t, after that I had to abort the mission and solve the car’s problem before continuing the experiment. That’s what happened last night. I hope I will be able to give you an update on this as soon as I make this circuit perfect.

What I learned until now is that this circuit is going to work on my car, but I need more time to make it work perfectly. In case you didn’t notice, I introduced a capacitor to the circuit as well which is supposed to make the headlights work for a little bit longer when the CDS is exposed to light after dark. This is supposed to avoid light flickering inside your car.

I hope you enjoyed today’s post. Until my next adventure with this project, please stay tuned to get more updates on it.

BMW E36 Blog: The ultimate E36 information source.

This is the second post in the series of how to create a device to turn your BMW lights on automatically when it gets dark. In the first post Turning Your BMW Lights On Automatically At Night, we’ve seen how it is possible to control a light using an electronic circuit that is sensitive to light. In that post, the idea was to create a circuit that will turn your BMW lights on when it gets dark and the videos proved to you that this can be done.

Today, I found the electronic circuit that can be used to create such a controller device. Take a look at this and please excuse the bad quality of the photo, I had to take it with my mobile camera instead of a scanner (it’s from a book):

Now for those of you who do not know anything about electronics, here’s an explanation:

To build this circuit, you will need the following:
1. PnP Transistor.
2. Battery (No, don’t buy one, you already have it under the hood).
3. Relay.
4. Variable Resistor (50 Kilo Ω (Ohms))
5. Light Sensitive Resistor.

Now, to understand how this circuit works, simply imagine the transistor as a switch that can be operated electrically by applying current to its base (the point in the middle), so, when we apply current to the transistor base, it will close the circuit on the other two points. This means that the battery and the relay will be in a closed circuit which makes the relay trigger and then turn the car lights on.

Now, how can we use light to trigger the transistor base? It’s simple. The resistance of the light sensitive resistor changes according to the light intensity. Its resistance becomes almost zero (0 Ohms) when there’s light and it becomes very high when it’s dark. So, using this circuit, the light sensitive resistor will trigger the transistor base when it’s dark.

I’m sure that you’re asking what is the benefit of the variable resistor, right? It’s used to control how sensitive this circuit is going to be for light. So, if you find that the car lights are being too sensitive, try to adjust this variable resistor and this problem will be fixed.

I hope you liked this second part of the series, please have a magnificent day guys and remember to stay tuned for the next posts on the BMW E36 Blog.

Update: I have reviewed the electronic circuit one more time and it seems that it has a problem, I’ve changed the circuit from the original post and I also changed the needed parts to implement it.

BMW E36 Blog: The Ultimate E36 Information Source.

I’m almost sure that everyone has seen the new cars that turn their lights on automatically when they go inside a dark tunnel or some other dark places. For me, I’ve seen this too many times and I have to admit that this option is very useful and at the same time very cool to add for our BMW cars. The only problem with this idea (you may call it a wish if you like) as far as I know is that our cars are old and this option was not available at their production time. Taking this into account, I was wondering how hard it would be to implement such an option without crying at the front door of BMW engineers. I’ve a little background about electronics and I believe this is definitely something that can be done, not by me maybe, but I’m sure it can be done.

To prove this, I’ve made some digging for information about light sensors and after overwhelming results about motion detectors and such stuff, I managed to find three sample videos that can prove this is possible and I believe it’s even easy (well, let’s not get carried away, let’s say "not hard" :D).

Take a look at the following videos:

The way I see it, this electronic circuit should:

1. Work at 12-Volts: It should rely on the car’s battery to run
2. It can be overridden: I think A tri-switch would be sufficient for this, hmmm . . . where can I get such a switch?

3. It should have some delay in response: This is important to avoid light flickering.

I hope you like this idea. Now I will need to try and find some specific details on how to implement it, so please stay tuned. I will keep you posted.

BMW E36 Blog: The Ultimate E36 Information Source.