Well I tried! Rear fog auto switching - BMW Luxury Touring Community
 
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post #1 of 12 Old Nov 3rd, 2007, 3:34 am Thread Starter
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Well I tried! Rear fog auto switching

Been playing with my electronics module to switch the spare rear bulb as a fog lamp. I also incorporated a system to flash it during brake application.

It all works fine on the bench, doing exactly what I ask of it. As soon as it is installed in the bike, POP..... magic smoke escapes.

So, if there are any electronics specialists that could look at my design I would appreciate it. It uses a 4082 CMOS which goes u/s.

Just pussin' through.
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post #2 of 12 Old Nov 3rd, 2007, 10:15 am
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What does your circuit look like? how are you testing it on the bench?

Jerry,

2002 LT -[MidLife]
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post #3 of 12 Old Nov 4th, 2007, 12:36 am
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Did you somehow mix up the polarity +/- ?? Or somehow short some connection that wasn't supposed to be shorted?

...Bob
2001 K1200LT der LadungsTräger
1978 GL1000
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post #4 of 12 Old Nov 4th, 2007, 2:48 am Thread Starter
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Well I have done the hookup twice and thought I was getting it right. As I have run out of 4082 until next week, I can't try it again until then. I have had a couple of thoughts though.

If I got the inputs for tail light and brake light mixed up, the CMOS would have had no power with inputs set high. I wonder if it should tolerate that?

I will scan my circuit diagram tomorrow and attach it, assuming it is not too far off topic? In brief, it is a four input AND gate. Input 1 is tied high. Inputs 2 and three come from the left and right turn signals. Input 4 comes from the brake light. The idea is that with hazards running, tail light on and brake applied, the output of the CMOS goes high and trips a thyristor, which sets a relay. This relay connects tail light circuit to the spare filament in the light unit. The power supply is the tail light circuit. All connections are available inside the light unit so no extra cables need to be run, ignoring legal requirements for indication etc!

The other half of the circuit is a 555 timer which also runs a relay wired as "two way switching" in the same line. The reset pin is held low and is also connected to the brake line circuit, so that when the brake comes on, the spare filament pulses, regardless of the fog lamp status.

Just pussin' through.

Last edited by Ajlelectronics; Nov 4th, 2007 at 3:20 am.
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post #5 of 12 Old Nov 4th, 2007, 3:37 am
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Without seeing your design I can only ask this. Are you regulating the power down to 12 volts? I think I read somewhere that the LT's alt puts out 14+VDC. Those extra volts could be your problem if you aren't regulating the power.
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post #6 of 12 Old Nov 4th, 2007, 3:42 am Thread Starter
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Quote:
Originally Posted by Morley
Without seeing your design I can only ask this. Are you regulating the power down to 12 volts? I think I read somewhere that the LT's alt puts out 14+VDC. Those extra volts could be your problem if you aren't regulating the power.
That's a thought, but testing was done with engine off.

I think it might have been powering up the inputs with no rail voltage if I got the connections wrong. I may incorporate a diode from each input to rail, so that can't happen, although I believe it should cope with it. CMOS are rated at 15V with brief excursions to 18V.

Just pussin' through.
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post #7 of 12 Old Nov 4th, 2007, 3:23 pm Thread Starter
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Yer tiz

Circuit diagram drawn from memory. Contemplating adding diodes from CMOS inputs to rail, so that it isn't possible to take inputs high with no supply.

Feel free to criticise or copy for your own bike (if it's any good!)
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Just pussin' through.
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post #8 of 12 Old Nov 4th, 2007, 7:12 pm
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If the chips you are using are good to 15V and you are still smoking them I would definately look into using some diodes. A while back I was playing with some auto electronics for a data communication cable and kept having communication problems, added a couple diodes to the grounds and it all cleared up.
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post #9 of 12 Old Nov 5th, 2007, 6:12 pm
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Hello from just over the Canal,

Been looking at your circuit (neat idea), and on paper it looks fine. Adding a couple of diodes won't do any harm, but I'd like too suggest spliting the circuit in two.

Build your fog lamp on circuit, and test that wired to the bike.
Build your flasher unit, and test that on the bike. (supply a temp feed to the bulb)

If each works fine independantly, then when you put them into one circuit, if it pops again, I'd look to try and isolate the supplies from each other again with a couple of diodes. I'm guessing you have a few mutlimeters kicking around, perhaps you can add them in the circuit to see where you are drawing the current which is blowing the AND gate, or putting a couple of small fuses into the circuit to pop before taking out the gate which would help to pinpoint the failure point.

been 10 years since I looked a circuit, just drawing on fault finding techniques.

Rgds
Mike

"For those that know, no explanation is needed,
For those that don't, no explanation is possible."

2001 K12 LT Toscana Green AKA Baby Sh*t Green
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post #10 of 12 Old Nov 5th, 2007, 8:13 pm
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circuit

Hi there I don't think it is a voltage problem ... I think you are pulling too much current. I have to look at the spec sheet.. but I would guess that the forward current rating it in milliamps...

Here are some sample I found when I was looking to do my led flasher..

http://www.uoguelph.ca/~antoon/circ/flashing.htm

http://www.csgnetwork.com/ne555c3.html

Jerry,

2002 LT -[MidLife]
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post #11 of 12 Old Nov 7th, 2007, 9:05 am Thread Starter
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All working now

It was a bit of a squeeze getting the module in, I thought it was fine at the trial fit!

I have kept to the same circuit, but added diodes from inputs to rail. I also removed the CMOS power feed tapped from the relay and fed the contacts from a fused battery supply. I did this because I could be pulling 4A or so and the wiring / OEM fuses may not have stood it.

Found a foglamp just lurking in the workshop, so added that in parallel with the spare filament. Now there should be no excuse for anyone to not see me.
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post #12 of 12 Old Nov 7th, 2007, 8:02 pm
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Congratz... looks good

Jerry,

2002 LT -[MidLife]
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