Seeking help with a circuit design

Topic: Seeking help with a circuit design (Read 4054 times) previous topic - next topic

Seeking help with a circuit design

June 13, 2012, 08:52:09 AM

One or two of you are talented electronics people, and I could use some help. I want to build an accessory delay timer for my Bird. Such a timer would receive a pwon signal from ignition on or acc, and would power up and hold a relay. The relay would remain energized for 10 minutes OR until a ground signal is given from a door ajar switch. There it is. I'm an electrical specialist at a Ford dealer, so I can build it and integrate it into the vehicle very easily, but my talents don't extend into electronic design. If anybody can help design the device, their help would be greatly appreciated.

Seeking help with a circuit design

Reply #1 – June 13, 2012, 07:43:52 PM

What first comes to mind when you said "10 minutes" is the relay similar to what runs the rear window defrost. It holds for about ten minutes when turned on, then shuts off, or it can be cancelled manually. But what I think you are trying to accomplish is to have it turn on automatically when the ignition is turned off, then either time out or be cancelled by a door opening? Such as the infamous "GEM" modules or "LCM's" in late model vehicles.

Seeking help with a circuit design

Reply #2 – June 13, 2012, 08:14:51 PM

You can probably find a time delay relay that will stay on for a set time after power is removed. That'd be your simplest option. If you really wanted to get into it you could build a time delay module using a 555 timer set up for astable operation (meaning the output stays live for a set time then goes out, as compared to stable operation which puts out a steady pulse). Have the 555 drive a relay to keep things live for your desired time, and have a second relay that resets the whole thing when the door is open. Set the second relay up to keep the circuit running when the relay is "off" (using terminal 87A on a standard bosch relay), and then killing it when the relay is live (by grounding terminal 85 or 86 through the dome light circuit).

If I get a chance I'll draw up a schematic for you, but that's a big "If" as I'm currently trying to get garage plans done up so as to obtain a permit, then I'll be busy trying to build the garage. You'll have to keep reminding me, as I will almost certainly forget...

Seeking help with a circuit design

Reply #3 – June 13, 2012, 09:18:27 PM

Have you looked into stamp controllers, pic's or an adruino board?

Might be a bit overkill, but they are fairly customizable.

Seeking help with a circuit design

Reply #4 – June 15, 2012, 02:19:39 AM

google RC time constants and there you have it,,, too easy.
a combination of a resistor and a capcitor in parallel will give you "TIME"
the relay will be the easy part for you,,,,,,,so there you have it, 50Cents and your out the door.

idealy you want to use a variable capacitor and variable resister and "dial in" the setting.

for free you can find these two parts on most trash circuit boards.

There are also RLC circuits (resistors, inductors and caps)

good luck ,, You are about to meet ELI the ICE man "XL" and "XC"

here is a decent link to do the math for you,,, basically your shooting for 640seconds
find the right combo of parts and you can do it for free.
http://hughestech.com/rc_calculator/

next google the resistor color code chart

there is a rhyme to remembering the color code but its no longer polictically correct.

an 800Kohm resistor and 800mico ohm capcacitor gets you close.

Seeking help with a circuit design

Reply #5 – June 15, 2012, 05:32:18 AM

Could you use a headlight timeout module. Or a dome light module that delays. Just saying.

Seeking help with a circuit design

Reply #6 – June 15, 2012, 06:56:21 AM

@Tom, I could, but I'm looking to duplicate the function of a modern cars accessory delay COMPLETELY. I want it to kick off when I open a door.

Seeking help with a circuit design

Reply #7 – June 15, 2012, 05:25:09 PM

Hook up another door ajar sensor.

Seeking help with a circuit design

Reply #8 – June 15, 2012, 08:44:24 PM

I can tap into the door ajar feeds I have, but what I need is a timer with a kick on trigger and a separate kick off trigger. And I need the timer to not start until the kick on is released.

Seeking help with a circuit design

Reply #9 – June 15, 2012, 09:10:56 PM

A 555 based circuit as I described would kick on as soon as you turned the key on and stay on as long as the key was on. Since the accessory circuit would be powered up by the key this would not be noticed, it would simply be a redundant accessory power source. Then when the key was off the 555 would hold power for a set amount of time. A ground input from the dome light circuit could reset the timer (resetting it would turn it off until the next key on cycle).

Seeking help with a circuit design

Reply #10 – June 16, 2012, 06:18:10 AM

I was looking into a 555, but it seems 10 minutes is too long an interval. I was referred to a 74c14.

Seeking help with a circuit design

Reply #11 – June 16, 2012, 06:22:59 AM

i wasn't aware the 555 had any time limits. you can change the time by changing values for resistors and capacitors.

Seeking help with a circuit design

Reply #12 – June 16, 2012, 06:30:12 AM

I was reading that the caps required to get out that far gave them problems and for longer intervals, the 74c14 was more ideal. I've never used either, thats just from my reading. I you know different, I'd be prepared to take your word for it.

Seeking help with a circuit design

Reply #13 – June 16, 2012, 07:37:10 AM

If (when) you get this figured I'd love to see a circuit diagram or link to where you found the answer. It sounds like a fun little feature to add to my junk.

Seeking help with a circuit design

Reply #14 – June 16, 2012, 05:39:17 PM

without spec sheets on the 555 timer, its still sorta mandaing a variable reisistor and capacitor....right back to the root of a timer circuit which as a resistor and capacitor anyway. so why not just use a reisistor and capacitor.