Author Topic: 2.5 Minute electronic delay circuit.  (Read 8772 times)

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Offline whittington

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2.5 Minute electronic delay circuit.
« on: April 08, 2009, 06:37:53 PM »
In one of my other post regarding Eyebrow Driving Led Strip Lights I installed on my car. http://www.mazda3forums.co.uk/index.php?topic=3172.0 I mentioned that with my model there is approx a 30 second delay of switching off the leds after the ignition is switched off. This was an unexpected bonus feature that has proved very useful, but subsequently I felt it would be very nice to have a much longer delay. So I have modified a well know simple transistor design to give me 2.5 minutes delay, plenty of time when getting home in the dark to find the front door!!!

The circuit works like this, ignition switched on +12 volts passes through the silicon diode and charges up the capacitor to +12 volts. This switches on the transistor on and this switches on the relay, this in turn switches on the leds.

When the ignition is switched off the +12 volt input disappears and the capacitor discharges via the resistor into the base of the transistor, the delay time is dependant on the value of CxR and the transistor gain relay resistance etc,  in my circuit when this voltage drops to  +1.6v the transistor switches the relay off and the leds go out. The silicon diode is simply to make sure that the capacitor does not find another backdoor path to discharge through!

The components used were found in my junk box, the transistor is 2N3055 is a bit of an over kill with it’s 115watt rating, but almost any silicon NPN transistor will do, the capacitor is 22,000uf 35 volt working the resistor is 1.8k ½ watt, the relay is a normally open contacts 12volt car type, the essential fuse is 3.5 amp.

The unit is built in a small plastic box and all components are super glued to the  base of the box, including the transistor,  which after giving in a long soak test doesn’t generate any heat so no need for a heat sink. See picture of finished box prior to installation.

The circuit diagram is in the attached folder at the bottom.
My thanks to a15acro (Andy) for his help in getting this diagram uploaded.

Here is the final picture

Colour code: Red +12v. Black Ground. Yellow to Ingnition on Switch. Blue to the leds.

[attachment deleted by admin]
« Last Edit: April 10, 2009, 08:53:32 AM by whittington »
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Offline Willpower

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Re: 2.5 Minute electronic delay circuit.
« Reply #1 on: April 09, 2009, 03:38:11 AM »
I think you might just have found yourself a niche and a probable queue of people that will want one.

What is the black protrusion on the left hand side with the red wires attached?
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Offline CPL

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Re: 2.5 Minute electronic delay circuit.
« Reply #2 on: April 09, 2009, 07:51:19 AM »
Looks like the fuse holder to me.

Offline whittington

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Re: 2.5 Minute electronic delay circuit.
« Reply #3 on: April 09, 2009, 08:51:14 AM »
I think you might just have found yourself a niche and a probable queue of people that will want one.

What is the black protrusion on the left hand side with the red wires attached?


Yes CPL is right its the fuse holder. I have had several replys from chaps to my question on how to get the circuit diagram uploaded, been a difficult job and lots of time trying to get that uploaded, so  hang on and it will be done but not for a day or so.
Thanks for your interest.
Pete
« Last Edit: April 09, 2009, 02:43:47 PM by whittington »
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Offline a15cro

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Re: 2.5 Minute electronic delay circuit.
« Reply #4 on: April 09, 2009, 09:55:52 PM »
Drawing

[attachment deleted by admin]
« Last Edit: April 09, 2009, 09:57:54 PM by a15cro »
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Re: 2.5 Minute electronic delay circuit.
« Reply #4 on: April 09, 2009, 09:55:52 PM »