Build a delay into Reverse camera ?

Me-262 · Post by **Me-262** » Mon Aug 10, 2009 5:10 am

http://www.youtube.com/watch?v=DIQ3oJveGAo

I installed a Kenwood DNX5140 Nav unit earlier this summer and hooked up a revsere camera shortly after. The Kenwood uses a "remote" wire that's hooked up to the reverse lights. When I put the car in reverse the display automatically switches to the reverse cam which is very handy.

No here's where I'd like to change things. The second you take it out of reverse the display switches back. Its my driving style but I pull it out of reverse about a second before I stop moving backwards so I am missing some "backing up time" . Not much but I notice it.

What could I connect inline that would continue to send a signal to the Kenwood for an additonal second or two after I pull out of reverse ? All I have done ( as intructed by the manual) is tap into the power wire for the reverse light. This seems to be a remote sensor no different than that an amplifier would use. I can hook gear up but have no clue as far as building electronics, what would you guys suggest to build that woud be small and simple ??

gkitching · Post by **gkitching** » Mon Aug 10, 2009 5:45 am

Do u wish it to continue to be activated and de-activated by going in and out of reverse? Cause u could always use a switched 12v+ to that wire instead of the reverse trigger.

Otherwise a delay on the + wire utilizing a small cap would give you a few seconds extra before shutting down. I have a diagram that I'll search up for making one of those. The trick is, u'll need to diode isolate that wire so it doesn't continue to feed 12v+ to the reverse lights also.

Me-262 · Post by **Me-262** » Mon Aug 10, 2009 6:32 am

Yeah, I want "hands free" operation. Put in in reverse , cam comes on . I can press a button on the Nav and it will stay on until I turn it off but that's a PITA. Cool thanks !

gkitching · Post by **gkitching** » Mon Aug 10, 2009 8:33 pm

here it is

gkitching · Post by **gkitching** » Mon Aug 10, 2009 8:36 pm

As for the size of the cap, the higher the uf the longer the delay. The exact time of the delay depends on the currant draw of the head unit.

Me-262 · Post by **Me-262** » Tue Aug 11, 2009 3:12 am

Thank you ! Now for the Diode what should I get or are they all the same ? Can I put this all on a little circuit board to keep it tidy ? Any way to figure out current draw from the HU without pulling the wires apart ? I do have a multimeter.

bretti_kivi · Post by **bretti_kivi** » Tue Aug 11, 2009 3:41 am

1N4001 diode should be fine, that will take 1A.

Bret

Post by **Eric D** » Tue Aug 11, 2009 8:50 am

I don't think the above circuit will work as a delay. As soon as the headunit trigger comes on it will start filling the capacitor with charge and allow 12V to pass to the other side of the diode. If the capacitor is completely empty it will draw max current from the trigger and may damage it.

Post by **ttocs** » Tue Aug 11, 2009 10:55 am

Recently used a similar idea to keep a relay engergized for a few secs after it lost power. The question is how much current it will draw that will answer how long of a delay it makes.

I don't think adding a cap on that leed would cause much trouble but unfortunatly only one way to check.

ProperID · Post by **ProperID** » Tue Aug 11, 2009 12:23 pm

Eric D wrote:I don't think the above circuit will work as a delay. As soon as the headunit trigger comes on it will start filling the capacitor with charge and allow 12V to pass to the other side of the diode. If the capacitor is completely empty it will draw max current from the trigger and may damage it.

The headunit isn't the trigger...the 12V is the trigger (the headunit is just sensing current on this wire).

Does this still make you think it will cause damage to the 12V circuit (in this case, the reverse lights) or the headunit sensor?

Post by **Eric D** » Tue Aug 11, 2009 6:13 pm

I am confused now. I don't understand the purpose of the diode in that circuit. I would guess a resistor should be in its place.

Post by **ttocs** » Tue Aug 11, 2009 10:33 pm

the diode keeps the cap from discharging back into the back-up circuit. If it were not there we would be building a delay to keep the back up lights on for probably .1 secs.

Post by **Eric D** » Wed Aug 12, 2009 6:00 am

The way the diode is in there will not allow 12V to come from the "12v + Reverse Wire" side to the 'To Headunit Trigger" side. If you turned the diode around, I don't see how there would be a delay, since when the "12v + Reverse Wire" goes active it will instantly fill the capacitor and the "To Headunit Trigger" side would be triggered.

ProperID · Post by **ProperID** » Wed Aug 12, 2009 6:05 am

It's not intended to cause a delay-ON....it's intended to cause a delay-OFF (keep the circuit energized for a moment....~1-2 seconds).

So the diode is backwards?

Post by **Eric D** » Wed Aug 12, 2009 6:26 am

This is my best guess as to what would work. When the backup lights go active, current will instantly flow through the diode and instantly charge the capacitor so the trigger will see 12V (well, not instantly but very close). When the backup lights go off, the diode will prevent current from flowing back, and the resistor will slowly discharge the capacitor. Once the capacitor voltage drops low enough the headunit will no longer be triggered. The value of the cap and resistor will have to be played with depending on the current draw of the headunit trigger, if any.

Post by **Eric D** » Wed Aug 12, 2009 6:31 am

ProperID wrote:It's not intended to cause a delay-ON....it's intended to cause a delay-OFF (keep the circuit energized for a moment....~1-2 seconds).

So the diode is backwards?

As the circuit was drawn I don't think the headunit would ever be triggered. The diode would prevent current from passing to the trigger. If you turned the diode around it would be instant on, and may have a delay off, but might never turn off. If the headunit uses a MOSFET gate trigger for example the cap would never discharge and the unit would be stuck in backup mode.

Me-262 · Post by **Me-262** » Wed Aug 12, 2009 6:34 am

I told you guys this would be more complicated than I could design !! Let's get it figured out before I start playing with anything.

Post by **Eric D** » Wed Aug 12, 2009 6:39 am

Me-262 wrote:I told you guys this would be more complicated than I could design !! Let's get it figured out before I start playing with anything.

Do you own a DMM?

Me-262 · Post by **Me-262** » Wed Aug 12, 2009 7:20 am

No, I don't even know what one is.

Post by **stipud** » Wed Aug 12, 2009 8:00 am

Me-262 wrote:No, I don't even know what one is.

A multimeter!

http://en.wikipedia.org/wiki/Multimeter

Post by **Eric D** » Wed Aug 12, 2009 8:04 am

If you don't have a DMM, you can make this work through trial and error (picking values for the parts). Also, so long as you wire it as shown you have no risk of damaging anything.

Me-262 · Post by **Me-262** » Wed Aug 12, 2009 12:27 pm

Ok, I thought it was some kind of PG gear. Yes , I do have a DMM in that case Please continue with your previous train of thought.

Post by **Eric D** » Wed Aug 12, 2009 12:29 pm

Put the DMM leads in the position required for current measurement. Put the DMM in DC current mode. Put one lead on the 12V backup light source, and the other lead on the headunit trigger (you would be using the DMM as a wire in this case). Enable the backup lights and measure the current traveling to the headunit trigger.

Once the current is known, the required time delay capacitor can be determined.

Me-262 · Post by **Me-262** » Fri Aug 14, 2009 4:18 am

Alright, I'm gonna need to tear apart some of the trim to get at that wiring then. I'll do some testing and report back.