Vet me this courtesy light circuit

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Overlord
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Vet me this courtesy light circuit

Post by Overlord » Thu Mar 06, 2008 12:49 pm

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 and a high side trigger to fire the maplights in the courtesy lighting circuit.
Problem was, I needed some sort of circuit to splice into the open ground line of the courtesy circuit just upstream of the door ground switch that will throw 12V+ on the map light circuit when the door switch closes (grounds) the circuit.

Then I got greedy.

As long as i was at it, why not have the timer maintain the original ground to keep the original courtesy lights on briefly after that ground was lost

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

Thus, trying to simplify.
Module should have it's own separate power and ground.
Module should trigger when when it becomes grounded thru the hot door ground switch.
Module should then;
1. initiate timing
2. trigger a +12 high to the map light line
3. maintain the courtesy circuit ground (thru the separate constant ground) and +12 high after the door switch ground is broken, for a short timed period
4. kill separate ground and +12 high signal and ideally draw no current until grounded thru the door switch again.

Got a schematic from a guy that supposedly does all that.
I haven't cobbled together circuits in a while and never with a 555.
How does it look to you?
-----------------------------------

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Overlord
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Post by Overlord » Thu Mar 06, 2008 12:50 pm

Posting the text file buggered it up.
Snagged the text window as an image and uploaded it.

Bigglez
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Re: Vet me this courtesy light circuit

Post by Bigglez » Thu Mar 06, 2008 8:51 pm

Greetings (No first Name Supplied),
Overlord wrote:Got a schematic from a guy that supposedly does all that.
I haven't cobbled together circuits in a while and never with a 555.
How does it look to you?
The text doesn't match the schematic. Take a look at the
LM555 datasheet to find the error.

Using the LM555(or equavalent) should work, but your
circuit is bear bones and does not have any protection
against the noisey unregulated DC power found in cars.

There is no fuse or other protection in the circuit to protect
against a wiring defect, shorted bulb(s), or stupidity.

Comments Welcome!

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Overlord
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Re: Vet me this courtesy light circuit

Post by Overlord » Fri Mar 07, 2008 7:54 am

Bigglez wrote:Greetings (No first Name Supplied),
Overlord wrote:Got a schematic from a guy that supposedly does all that.
I haven't cobbled together circuits in a while and never with a 555.
How does it look to you?
The text doesn't match the schematic. Take a look at the
LM555 datasheet to find the error.

Using the LM555(or equivalent) should work, but your
circuit is bear bones and does not have any protection
against the noisey unregulated DC power found in cars.

There is no fuse or other protection in the circuit to protect
against a wiring defect, shorted bulb(s), or stupidity.

Comments Welcome!
Off the top of my head;
Certainly I would fuse the module. The courtesy lights have been replaced with LED strips and shouldn't draw much current (tho 1 strip is some 36" long).
Wouldn't mind a diode in the switched ground point B as the switched ground is normally hot until grounded.
Don't like the +12 supply wired through the resistor to the switched ground point B.
Not so hot on the reset pin 4 being always hot.

Other than that, I'd have to research the 555 data. Never used one and pretty rusty on designing circuits anyway. I'm more of a cookbook guy these days.

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jollyrgr
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Post by jollyrgr » Fri Mar 07, 2008 4:26 pm

There is a much easier way to do this. You need to find the common location of the ground point for the courtesy lights. Make sure both, all four, or whatever number of doors you have are connected to one side of the wire. Now disconnect (cut???) the wire so you have one end going to the lights, the other to the grounding switches.

Connect a relay such that it is going to +12V on one side of the coil. The other goes to the ground switches. Put a cap in parallel with the coil. Now as the switch grounds the relay, it will energize and charge the cap. The coil will remain energized until the cap discharges when the ground is removed. (Experiment or work the RC constants based on your time requirement and relay coil impediance.)

Now you take the wire that was previously grounded by the door switches and connect it to the relay Normally Open contact. Connnect the relay wiper to ground. When the relay energizes the lights come on (as soon as the door is opened). When you close the door, the relay starts to discharge the cap but will keep the lights turned on as they are being grounded by the relay.

I wish I could recall more about this circuit that worked in a similar fashion. I know in at least one setup this could be done without cutting any wires. This circuit used two ground paths and a blocking diode. Grounding the switches caused the light to go on. Removing the ground caused the relay to stop receiving power and would drop the ground after the cap discharged. This circuit connected to +12V, to ground, and tapped into the ground side of the courtesy light. It would sense the grouding of the open door but would not "lock up" by seeing the relay ground.
No trees were harmed in the creation of this message. But billions of electrons, photons, and electromagnetic waves were terribly inconvenienced!

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Overlord
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Post by Overlord » Sat Mar 08, 2008 7:12 am

jollyrgr wrote:There is a much easier way to do this. You need to find the common location of the ground point for the courtesy lights. Make sure both, all four, or whatever number of doors you have are connected to one side of the wire. Now disconnect (cut???) the wire so you have one end going to the lights, the other to the grounding switches.

Connect a relay such that it is going to +12V on one side of the coil. The other goes to the ground switches. Put a cap in parallel with the coil. Now as the switch grounds the relay, it will energize and charge the cap. The coil will remain energized until the cap discharges when the ground is removed. (Experiment or work the RC constants based on your time requirement and relay coil impediance.)

Now you take the wire that was previously grounded by the door switches and connect it to the relay Normally Open contact. Connnect the relay wiper to ground. When the relay energizes the lights come on (as soon as the door is opened). When you close the door, the relay starts to discharge the cap but will keep the lights turned on as they are being grounded by the relay.

I wish I could recall more about this circuit that worked in a similar fashion. I know in at least one setup this could be done without cutting any wires. This circuit used two ground paths and a blocking diode. Grounding the switches caused the light to go on. Removing the ground caused the relay to stop receiving power and would drop the ground after the cap discharged. This circuit connected to +12V, to ground, and tapped into the ground side of the courtesy light. It would sense the grouding of the open door but would not "lock up" by seeing the relay ground.
This is the original relay controlled circuit someone made. I'm curious about the diodes but it would appear to be a cut/spliced in section like you are talking about. In fact, I could cut the line to the passenger door and simply run another wire/diode from C1 to the other door switch.
Does this one look something like what you were talking about?

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Post by dyarker » Sat Mar 08, 2008 10:56 am

D1 allows C1 to discharge slowly through coil of Rly1; giving the delay you want. Without D1, C1 would discharge quickly through the courtesy lights when the door is closed.

D2 and D3 suppress the reverse voltage spike when current through the coils is switched off. D2 probably isn't needed because of D1 and C1, but is good practice and cheap insurance.

Cheers,
Dale Y

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Overlord
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Post by Overlord » Fri Mar 14, 2008 8:37 am

I'll start on the circuit today or tomorrow.
In the spirit of Steinmetz' divine discontent, I will look at eventually setting up a current limiting dimmer for the LEDs. It wouldn't work on the map light LEDs as they just have the trigger line and are entirely internal to the RV mirror. Putting it inline with the strings of LEDs in the cargo area and footwells. Not putting it in the delay circuit as I suspect that is just downstream from a relay. Have to find time to go over the car schematic and nail that down.

thanks all.

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