ineterior l.e.d.s, door pins and relays

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Forum Name: Lights, Neon, LEDs, HIDs
Forum Discription: Under Car Lighting, Strobe Lights, Fog Lights, Headlights, HIDs, DRL, Tail Lights, Brake Lights, Dashboard Lights, WigWag, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=57037
Printed Date: May 14, 2025 at 2:51 AM

Topic: ineterior l.e.d.s, door pins and relays

Posted By: GBone21
Subject: ineterior l.e.d.s, door pins and relays
Date Posted: June 04, 2005 at 5:41 PM

I am sure this is easy for someone...I have searched and can not seen to find the answer to this one. I have an '87 RX-7 and have added a lot of neat things to it....alarm, remote trunk popper, power door locks, l.e.d.'s, remote window roll down, etc. I have a peripheral VT3 which is an audjustable timer interface. Now, the question. I would like to have some l.e.d.s hooked up around my amp rack that come on when you open the door and stay on for about 30 seconds. Rght now when I open the door the interior lights come on, but not the l.e.d.'s, but when I shut the door the l.e.d's come on, and the dome ligh goes off. Also, if I don't want to put these on a timer, how can I make these come on when I open the door. I dont want to hook them up to the same circuit as the dome light or door lights. I have the l.e.d.'s hooked up to the drivers door pin switch. So the dome light comes on when I open the door, I also want my l.e.d.'s to turn on, but be on a timer and turn off after a set amount of time whether or not the door shuts. I think I need to turn the + signal from the door switch to a - signal? But the led's have power when the door pin switch is pushed in, which turns off the dome light..see my dilema? Any help would be great, thank you. I hope that some one understands all of this rambling.

greg

Replies:

Posted By: face
Date Posted: June 04, 2005 at 5:53 PM

it sounds like you have to hook up a relay to convert the polarity of the door trigger wire that should take care of the problem.

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The One And Only

Posted By: GBone21
Date Posted: June 04, 2005 at 9:45 PM

that didn't work.

Posted By: texas_aggie
Date Posted: June 14, 2005 at 1:14 AM

Maybe this will work. The 74LS121 will produce an output pulse set by the values of R1 and C1. Pin 5 of the 74LS121 is a Schmitt trigger input. Once U2 detects a positive edge on pin 5 it will produce an output pulse of approximately 28 seconds then the output will go low and it will wait for another positive edge. The output pulse is used to turn on U3 which is a solid state relay driver designed especially for 12 volt relays and can be used with relays up to 500mA. U1 is a positive voltage regulator and is only there to provide a clean +5V to the 74LS121, if you already have a good +5V source in your car you don't need the 7805. Pin 5 of the 74LS121 is a TTL logic level input and only needs 4V to 5V to detect a high state. I added R2 assuming your input signal was +12V, you might have to play around with this value depending on the current draw of the input of the 74LS121. I have not built this curcuit so I have no idea if it will actually work for you purpose. I have never tried to use a +12 volt source for an input trigger to a 74LS121 so R2 is only a guess. DigiKey does sell all of these parts in single quantities.

Note: You can build a cuircuit based on this design but using a 74LS221 and a SC-74 case 318F if you need two inputs and two outputs with independent delay times. 74LS221 is a dual version of the 74121 and the Case 318F is a dual version of the 318. You would need an addition R1 R2 and C1. The output pulse time is roughly .7*R1*C1 2k-40k resistors and up to 1000uF caps may be used.

Posted By: Theshadow27
Date Posted: June 15, 2005 at 3:10 PM

all you need is a:

Constant to Momentary Output

The capacitor allows the coil of the relay to be energized until the capacitor stores a charge, thus de-energizing the coil. The resistor bleeds off the charge of the capacitor when positive voltage is removed from the other side of the coil. You can increase the output time by simply changing the value of the capacitor. This one will give you about a 1/2 second output.
posted_image

you dont need a timer module and you dont need to hook into the dome light. instead of hooking the "switched 12v" up to the door pin, hook it up to constant power. then hook the ground connection (3 lines getting smaller) into the door pin. the capacitor size decides the delay, and it has a built in relay posted_image