Re: [DML] Re: DIY Door Light Switch Upgrade: Magnetic Switches

[Joe Angell <jangell@xxxxxxxxxxxxxxxxx>]

>   Very nice write-up! It is nice to have someone take the time to
> present such a detailed description.

Thanks

>   If I may add a few thoughts. The "proximity switches" come in 3
> types, the most common is "form A" which is closed circiut in the
> presence of a magnet (and most common because they are used in alarm
> systems). Then there is "form B" that is open ciruit in the presence
> of a magnet (good for door switchs since they draw no current when the
> door is closed).

That's what I thought and was what I was trying to get, but for some  
reason it operated opposite of what I expected.  I might have just  
gotten my order wrong.

> "Form C" has both open an closed circuits (3-wire SPDT).

Ah, I didn't know about those.  Cool.

>   I built a similar circuit for my car and wanted to share a few
> things I learned. With normal bulbs, the D's door lights pull about 1
> AMP each side. It is abut 1/10 that or 100 mA with LEDs. The typical
> magnetic switchs is rated for 500 mA for form A and 250 mA for form B.
> So, it is probably good that you used the transistor.

I also have LEDs in my doors.  I admit it didn't occur to me that I'd  
overpower the switches if I was still using normal bulbs.  Looks like  
I just got lucky. :)

> I used the form B switch with a relay so I could do the function of  
> both of the
> driver's side switches with one magnetic switch. The down-side of the
> relay is that you have to wire it to a power source under the dash
> (only used when the door is open). It would have probably been simpler
> to use a transistor like you!

I actually wanted to just use a single magnetic switch, but I  
couldn't quite figure out a good way to do it with one switch.  And I  
didn't think of finding an SPDT one.  Or a DPDT one, although I'm  
guessing those are pretty hard to find.

I avoided a relay only because I was concerned about having it  
energized while the doors were closed, thus unnecessarily draining  
the battery by some small amount, and I figured the transistor would  
draw much less power.  I was probably a little too paranoid there.   
Even so, the transistor setup also required an extra power source to  
function.

>  I too, really like the results. I never have to worry about the
> switch alignment again. There is no contact between the magnet and the
> switch.
>   Again, I appreciate the write-up.

No problem.  Thanks for the extra info!

-- Joe



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