Hey all.
I have a car with courtesy lighting circuit that is always hot. When
the doors are opened it grounds the system and the lights come on.
I spliced into the car an electronic rear view mirror with a separate
line to hook the maplights into the courtesy lighting circuit.

Problem is, I need some sort of circuit to splice into the open ground
line of the courtesy circuit that will throw 12V+ on the map light
circuit when the door switch closes (grounds) the circuit.

It would be nice to incorporate a timer to keep the lighting on for a
period of time after the ground is lost but that might be muddying the
waters a little much.

Persumably I could simply put a relay with the coil inline in the
open ground courtesy circuit to throw a separate line from the fuse
box to the map lights but that almost seems a little....shoddy.

The filament courtesy lights have been replaced with 34" LED strips
behind the seats and in the footwells. I'm not that certain what the
voltage drop of an inline relay would mean for them.

So I need either a schematic to sense the voltage drop as the hot
courtesy circuit is grounded and port 12V+ to the maplight line, or a
more elaborate schematic to maintain the ground (timer) and also
maintain the 12v to the maplights for a period of time, say 10 seconds
or so after the ground is interrupted.

I suppose I could do 2 separate systems but 1 would be more elegant.

Anyone like to take a stab at it?

Thanks,
Kurt
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Overlord wrote:
> Hey all.
> I have a car with courtesy lighting circuit that is always hot. When
> the doors are opened it grounds the system and the lights come on.
> I spliced into the car an electronic rear view mirror with a separate
> line to hook the maplights into the courtesy lighting circuit.
>
> Problem is, I need some sort of circuit to splice into the open ground
> line of the courtesy circuit that will throw 12V+ on the map light
> circuit when the door switch closes (grounds) the circuit.
>
> It would be nice to incorporate a timer to keep the lighting on for a
> period of time after the ground is lost but that might be muddying the
> waters a little much.
>
> Persumably I could simply put a relay with the coil inline in the
> open ground courtesy circuit to throw a separate line from the fuse
> box to the map lights but that almost seems a little....shoddy.
>
> The filament courtesy lights have been replaced with 34" LED strips
> behind the seats and in the footwells. I'm not that certain what the
> voltage drop of an inline relay would mean for them.
>
> So I need either a schematic to sense the voltage drop as the hot
> courtesy circuit is grounded and port 12V+ to the maplight line, or a
> more elaborate schematic to maintain the ground (timer) and also
> maintain the 12v to the maplights for a period of time, say 10 seconds
> or so after the ground is interrupted.
>
> I suppose I could do 2 separate systems but 1 would be more elegant.
>
> Anyone like to take a stab at it?
>
> Thanks,
> Kurt

Here's 2 approaches, below. The first uses relays,
the second a 555 & transistors.

_Relays_ You can do it with 6 parts.


+12 ------+----+----+----+-------+
|+ | | |Rly1-1 |
[C1] [D2] [Rly1] | <| |
| |a | | |
+----+----+ | |
|a +----+ |
[D1] | | |Rly2-1
| [D3] [Rly2] | <|
Switched Gnd ---+ |a | |
| | +---> + to map lites
Constant Gnd ----------------+----+


Rly1 is a low current relay, #528-117-3 from Mouser.
The switched ground will energize it immediately.
C1 (4700 uF, 25v) will hold it energized after the door
closes for a little over 5 seconds. Put a second 4700 uF
cap in parallel for ~double that. The Rly1 contact
energizes Rly2, which can be a heavy duty automotive
relay, if required. The Rly1 can switch up to 1/2 amp,
so if your map lites draw less than that, you can
eliminate Rly2 and D3. IN4001 diodes will work fine.



_555 and transistors_

TIP42C
+12 ----+------+-+-----+----+-----e c---> + to map lights
| | | | | \ /
| | | | | ---
| | | | | |
| | | | | [150R]
| | | | | |
| | | [1K] +-[10K]-+
| | | | |
[33K] 4 8 [POT]<-+ |
| ----- | | |
B ---+---2|-----|6--+----+ |
| | | c/
+----5| 555 |3------[1K]---| NPN
| | | | e\
[.01] ----- [100uF] |
| 1 | |
| | | |
Gnd----+-------+-------+------------+

With a 100K pot, you can adjust the stay on time
from about .1 to 11 seconds. Point B (see pin 2
of the 555) goes to the switched ground line.
Note that pin 6 is connected to pin 2 and that
there is no connection to pin 7.

Ed

ehsjr wrote:
> Overlord wrote:
>
>> Hey all.
>> I have a car with courtesy lighting circuit that is always hot. When
>> the doors are opened it grounds the system and the lights come on.
>> I spliced into the car an electronic rear view mirror with a separate
>> line to hook the maplights into the courtesy lighting circuit.
>>
>> Problem is, I need some sort of circuit to splice into the open ground
>> line of the courtesy circuit that will throw 12V+ on the map light
>> circuit when the door switch closes (grounds) the circuit.
>>
>> It would be nice to incorporate a timer to keep the lighting on for a
>> period of time after the ground is lost but that might be muddying the
>> waters a little much.
>>
>> Persumably I could simply put a relay with the coil inline in the
>> open ground courtesy circuit to throw a separate line from the fuse
>> box to the map lights but that almost seems a little....shoddy.
>>
>> The filament courtesy lights have been replaced with 34" LED strips
>> behind the seats and in the footwells. I'm not that certain what the
>> voltage drop of an inline relay would mean for them.
>>
>> So I need either a schematic to sense the voltage drop as the hot
>> courtesy circuit is grounded and port 12V+ to the maplight line, or a
>> more elaborate schematic to maintain the ground (timer) and also
>> maintain the 12v to the maplights for a period of time, say 10 seconds
>> or so after the ground is interrupted.
>>
>> I suppose I could do 2 separate systems but 1 would be more elegant.
>>
>> Anyone like to take a stab at it?
>>
>> Thanks,
>> Kurt
>
>
> Here's 2 approaches, below. The first uses relays,
> the second a 555 & transistors.
>
> _Relays_ You can do it with 6 parts.
>
>
> +12 ------+----+----+----+-------+
> |+ | | |Rly1-1 |
> [C1] [D2] [Rly1] | <| |
> | |a | | |
> +----+----+ | |
> |a +----+ |
> [D1] | | |Rly2-1
> | [D3] [Rly2] | <|
> Switched Gnd ---+ |a | |
> | | +---> + to map lites
> Constant Gnd ----------------+----+
>
>
> Rly1 is a low current relay, #528-117-3 from Mouser.
> The switched ground will energize it immediately.
> C1 (4700 uF, 25v) will hold it energized after the door
> closes for a little over 5 seconds. Put a second 4700 uF
^ 10 seconds
> cap in parallel for ~double that. The Rly1 contact
> energizes Rly2, which can be a heavy duty automotive
> relay, if required. The Rly1 can switch up to 1/2 amp,
> so if your map lites draw less than that, you can
> eliminate Rly2 and D3. IN4001 diodes will work fine.
>
>
>
> _555 and transistors_
>
> TIP42C
> +12 ----+------+-+-----+----+-----e c---> + to map lights
> | | | | | \ /
> | | | | | ---
> | | | | | |
> | | | | | [150R]
> | | | | | |
> | | | [1K] +-[10K]-+
> | | | | |
> [33K] 4 8 [POT]<-+ |
> | ----- | | |
> B ---+---2|-----|6--+----+ |
> | | | c/
> +----5| 555 |3------[1K]---| NPN
> | | | | e\
> [.01] ----- [100uF] |
> | 1 | |
> | | | |
> Gnd----+-------+-------+------------+
>
> With a 100K pot, you can adjust the stay on time
> from about .1 to 11 seconds. Point B (see pin 2
> of the 555) goes to the switched ground line.
> Note that pin 6 is connected to pin 2 and that
> there is no connection to pin 7.
>
> Ed