Hi all, hi Ya’akov.

My previous (relay mute) project is running nicely for 4 months now.

Time for a new BMW project. This time, I want to add extra LED lights in the trunk.


I thought there could be an easier way, instead of tapping into the trunk lighting switch and pulling wires into the trunk of the car.

My thought was that this can be remotely triggered. ie.
A. trunk opened, sends a remote signal to the receiver, which then switches ON the light.
B. trunk closed, sends a remote signal to the receiver, which then switches OFF the light.

The solution should be :
1. very low power consumption since it will be on continuously.
2. composed of existing off the shelf components that anyone can buy. (just like in my last project with the relay)

Fire away!

 

very low power consumption since it will be on continuously.

If using the existing battery in the vehicle it will still involve getting into the wiring so don't see the need for wireless.

 

The battery wiring is a 2 minute job and I already have the wires ready (waiting for the LEDs).
But even if it wasn't, it's the challenge that counts. ie. can I do this... is it feasible..is it viable?

 

Feasible using this style relay module with one additional resistor and magnetic switch for the trunk.

 

Using the magnetic trunk switch would only require 2 components (R1 and Q1) if you wanted to construct this simple circuit.

View attachment 327773

 

Great idea. Thanks.
BTW, do you know if there is a light/radiowave sensor that can sense if the trunk is opened at night (and day of course)?

 

Not right off hand but seems that would be over complicating things. The mag switch is passive, works both day and night.

 

Very true.

Using the magnetic trunk switch would only require 2 components (R1 and Q1) if you wanted to construct this simple circuit.
View attachment 327771

Are you saying I can buy any magnetic sensor from here and R1 & Q1 and I am done?
If so, what do you suggest for Q1? R1=1MOhm?
(I understand quite a bit but if I do not know something I will ask)

 

Are you saying I can buy any magnetic sensor from here and R1 & Q1 and I am done?

Yes with these two components. N channel mosfet Q1 and 1 meg ohm resistor R1.

 

I will be back in 12 hours

Yes with tha

Yes with these two components.
View attachment 327774

Q1 is a transistor, but without knowing the exact model no. I cannot go this route. In my country there are a handful of shops that might stock a small number of electronics components. It is not easy for me to play around.
Might be better to follow your initial recommendation and go with the relay.

I will be back in 12 hours to continue. Thanks.!!

 

If I know what you have available can probably suggest an alternate for Q1 and R1.
Why can't the transistor be ordered if need be?
Also need some specs on the LED module ordered.

 

Sure, I can order a Q1 & R1 from Mouser or Aliexpress. (There is no electronics available in my country)
My LED is the 81 LED long version here: https://www.aliexpress.com/item/1005006282413366.html
It is mentioned as 12W and I will use 2 of them!

 

I cannot find IRF544 anywhere - seems rare?.

 

Also the R1 how many watts should it be ??

Keep in mind that mouser will charge me 20 Euro for any delivery (even for just one resistor).
Whereas aliexpress will be reasonable.
e.g. https://www.aliexpress.com/item/1005003818765637.html
0.51 Euro (1.20 incl shipping) is decent .

I also found a project box for it 69x42x23mm 0.73 Euro (1.37 incl shipping).
https://www.aliexpress.com/item/1005006381428975.html

And the 2.2K resistor you mentioned in your diagram 0.55 Euro (1.48 incl shipping):
https://www.aliexpress.com/item/1005001934415707.html

Total 4.05 all inclusive.

 

Also the R1 how many watts should it be ??

1/4 watt is fine.
You still prefer using the relay module?

 

You still prefer using the relay module?

I know it is bulkier... unless I can source the transistor cheaply.
Maybe you can suggest an alternative transistor from Ali if you have time?

 

Maybe you can suggest an alternative transistor from Ali if you have time?

IRF540N mosfet on Ali.

 

Or IRF540 on DIGIKEY, US$0.70 , Digikey automatically send them to me in Canada,, next day air

 

Ali is like Amazon get 10 for the price of 1. That scares me!

 

Yes with these two components. N channel mosfet Q1 and 1 meg ohm resistor R1.
View attachment 327775

I found the MOSFET https://www.aliexpress.com/item/1005005933352536.html.
How about R1... how many watts?
Is 2W OK? https://www.aliexpress.com/item/1005006172485377.html