Coppertop
Feb 24th, 07, 7:19 PM
Okay folks, for those of you that were interested:
http://home.neb.rr.com/postmodern/dome.jpg
This circuit will give you an approx. 10 sec. "delayed off" after closing the doors or rotating the headlight knob for dome operation. I reworked my design to use all parts that should readily be available at RadioShack stores or RadioShack.com.
The beauty of this circuit is its simplicity, simple R-C time constants get the job done. Also, it contains something the other ones out there don't have--the rapid off feature just like modern GM products!
I'll post some pics when I get time.
For installation:
Open your car's trunk, locate the orange and white wires that feed up to the dome light.
Cut the the white wire in two. The half that feeds up to dome light connects into circuitry point "D".
The other half of the white wire that feeds back into the vehicle's harness gets connected into circuitry point "B".
Make a "tap" off the orange wire to provide power to the circuit. Don't cut it though--it still needs an un-interrupted path to the dome light. This tap will feed into circuitry point "A" on the schematic.
Circuitry point "C" is optional--if you want the rapid off just like modern GM vehicles, run a wire under the carpet to the fuse box (make sure you put a 1/2 amp fast-blo fuse in line to protect this feed). So in other words "C" will connect into the IGN terminal on your fuse box.
All ground symbols tie together and connect to a good bare metal body ground in the trunk.
Here are the RadioShack part #'s:
TIP120 Darlington NPN transistor: 276-2068
Heat Sink (use this attach to the above): 276-1368
470 uF capacitor: 272-1030
PN2907 PNP transistor: 276-2023
1k resistor (comes in 5 pack): 271-1118
10k resistor (comes in 5 pack): 271-1126
330 ohm resistor (comes in 5 pack): 271-1113
2N4401 NPN transistor: 276-2058
Of course you'll want a piece of perf board, some 4-40 machine screws, wire, misc. etc for building. I plan on putting this in a little project box, like RadioShack part #: 270-1801.
Theory of Operation
The orange wire in your dome light circuit has battery power at all times, this provides the power to the circuit and the (+) connection to the dome light itself.
The white wire in your dome light circuit used to provide the ground connection directly to the light to make it come on. Now the white wire provides the ground "signal" to the circuit.
When a door opens the ground provided to point "B" drives the PNP transistor into saturation, this allows a current path to charge the 470 uF capacitor thru the 330 ohm surge resistor as well as generate base current thru the 10k resistor turning on the NPN darlington pair transistor. This transistor grounds the dome light (-) connection and makes it turn on.
When the door(s) close, the PNP transistor turns off. Now the capacitor begins to discharge thru the 10k resistor and base current still flows thru the NPN darlington keeping the dome light on. Once there is not enough base current thru the darlington from the now depleted capacitor the dome light goes off (this circuit will give you an approx. 10 second delay).
The rapid off feature:
No one likes to have to wait to the dome light turns off to leave a parking space, (cause it's annoying to drive off with the light still on) if you're in a hurry after slamming the door.
Once you turn the ignition on, +12 volts is feed into point "C". This drives the NPN transistor into saturation, the capacitor now has another discharge path; thru the 1k resistor to ground. This rapidly depletes the capacitors charge so the dome light goes off within a second.
As long as the car is running, the dome light will go off instantly once the door's shut.
Have fun :D
http://home.neb.rr.com/postmodern/dome.jpg
This circuit will give you an approx. 10 sec. "delayed off" after closing the doors or rotating the headlight knob for dome operation. I reworked my design to use all parts that should readily be available at RadioShack stores or RadioShack.com.
The beauty of this circuit is its simplicity, simple R-C time constants get the job done. Also, it contains something the other ones out there don't have--the rapid off feature just like modern GM products!
I'll post some pics when I get time.
For installation:
Open your car's trunk, locate the orange and white wires that feed up to the dome light.
Cut the the white wire in two. The half that feeds up to dome light connects into circuitry point "D".
The other half of the white wire that feeds back into the vehicle's harness gets connected into circuitry point "B".
Make a "tap" off the orange wire to provide power to the circuit. Don't cut it though--it still needs an un-interrupted path to the dome light. This tap will feed into circuitry point "A" on the schematic.
Circuitry point "C" is optional--if you want the rapid off just like modern GM vehicles, run a wire under the carpet to the fuse box (make sure you put a 1/2 amp fast-blo fuse in line to protect this feed). So in other words "C" will connect into the IGN terminal on your fuse box.
All ground symbols tie together and connect to a good bare metal body ground in the trunk.
Here are the RadioShack part #'s:
TIP120 Darlington NPN transistor: 276-2068
Heat Sink (use this attach to the above): 276-1368
470 uF capacitor: 272-1030
PN2907 PNP transistor: 276-2023
1k resistor (comes in 5 pack): 271-1118
10k resistor (comes in 5 pack): 271-1126
330 ohm resistor (comes in 5 pack): 271-1113
2N4401 NPN transistor: 276-2058
Of course you'll want a piece of perf board, some 4-40 machine screws, wire, misc. etc for building. I plan on putting this in a little project box, like RadioShack part #: 270-1801.
Theory of Operation
The orange wire in your dome light circuit has battery power at all times, this provides the power to the circuit and the (+) connection to the dome light itself.
The white wire in your dome light circuit used to provide the ground connection directly to the light to make it come on. Now the white wire provides the ground "signal" to the circuit.
When a door opens the ground provided to point "B" drives the PNP transistor into saturation, this allows a current path to charge the 470 uF capacitor thru the 330 ohm surge resistor as well as generate base current thru the 10k resistor turning on the NPN darlington pair transistor. This transistor grounds the dome light (-) connection and makes it turn on.
When the door(s) close, the PNP transistor turns off. Now the capacitor begins to discharge thru the 10k resistor and base current still flows thru the NPN darlington keeping the dome light on. Once there is not enough base current thru the darlington from the now depleted capacitor the dome light goes off (this circuit will give you an approx. 10 second delay).
The rapid off feature:
No one likes to have to wait to the dome light turns off to leave a parking space, (cause it's annoying to drive off with the light still on) if you're in a hurry after slamming the door.
Once you turn the ignition on, +12 volts is feed into point "C". This drives the NPN transistor into saturation, the capacitor now has another discharge path; thru the 1k resistor to ground. This rapidly depletes the capacitors charge so the dome light goes off within a second.
As long as the car is running, the dome light will go off instantly once the door's shut.
Have fun :D