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Discussion Starter #1
I am wondering if anyone else has experienced this:

I was running my carputer when I decided to stop for gas. I did not shut down the PC as it was directly connected to the battery, and I could keep it running. I exited the car and tried to lock and set the alarm while going inside to pay. No matter which buttons I pushed, nothing worked. I hurried back inside and turned the pc off, then everything went back to normal. I could lock the doors and set the alarm with no problems. I ran the experiment again, making sure that the only connection was to the battery and nothing else, the same thing happened again untill I shut down the PC.

Is there some mechanism that will keep you from using your fob to lock and set your alarm if there is current draw from the battery? Has anyone else with aftermarket stuff experienced this? I double checked and the only thing connecting the pc to the car is the wire than runs to the battery. Everything else is powered off the PC, including the monitor. :8:
 

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I would guess your key was in the ignition, set to accessory. No alarm function will work with the key in the ignition.
 

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Discussion Starter #3
No. I turned the engine off and removed the key. I actually used the fob on that set of keys to lock the door and it would not let me. You know, I am going to turn the headlights on and create a current draw that way to see if that also prevents the doors from getting locked. I don't see what else could be responsible....
 

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Mr. 3 K, 3/3/5. 5K,10/5/7
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It may be that the RF interference from the PC is blocking the Fob from Communicating. How is your shielding? Maybe their is an interference from the power supply in the PC up the line. Maybe A couple of Ferrite's.
 

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I think you maybe right GripperDon. I did the test and with headlights on the fob had no problems. So it is NOT current draw that is doing this. I can get Ferrites from Radio Shack but where do I put them? On the power lines going to PC and the Monitor?
 

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Very interesting indeed.

I guess the Murano is a special case. I had aftermarket foglights on my 97 Maxima directly connected to the battery, and was able to arm the stock alarm with them still left on.

Worst comes to worst, you could always use your key on the door lock (gasp). :D
 

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Discussion Starter #7
Eric L. said:
Very interesting indeed.

I guess the Murano is a special case. I had aftermarket foglights on my 97 Maxima directly connected to the battery, and was able to arm the stock alarm with them still left on.

Worst comes to worst, you could always use your key on the door lock (gasp). :D
And chance scratching the thin coating they call paint???? No way! I rather get rid of the carputer!

At any rate, current draw is not causing the problem because I turned on a bunch of lights and it did not affect the alarm or door locks. It must be RF interference from the PC so I am hoping someone will direct me to what I need to do to shield the stuff.
 

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Mr. 3 K, 3/3/5. 5K,10/5/7
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I would get a little book from Radio shack or Google it and do a little reading. Basically the ferrite's are about the size Of A life saver. you wind the power input wires to the carputer around them a few times up close to the carputer. Also is the Carputer a metal or plastic box. If plastic some copper tape covering the box should do the trick, might be nice to ground it.
 

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Discussion Starter #9
I'll get a couple of Ferrites and put them on. The box is metal and is grounded but I will run another ground wire to it just to be sure.

Thanks!
 

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Mr. 3 K, 3/3/5. 5K,10/5/7
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Basically they choke the high frequencies travling down the surface of the wires. They make snap on ferrites also. I am sure you have seen a variety of types on printers, modems etc.
 

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zebelkhan...this is one interesting phenomenon indeed :)

Anyway, did you use Desktop PC for your carputer? Metal case/box?
I wonder if this issue will happen when one uses a laptop as the carputer core. Laptops are better insulated I presume.
 

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Discussion Starter #14
Dennis Fink said:
zebelkhan,

In another thread, you mentioned installing a USB GPS receiver in the speaker cavity of the driver's side dash.

Perhaps it is causing some interference.
Have you tried disconnecting it?
No. I did not think about that. I will try it. Did not get to go to Radio Shack last night so still no filters but according to link provided by GripperDon the type they have may not even help. I will test disconnecting the GPS receiver from PC to see if it is the problem.

SugarRush, this is a mini itx carputer with metal case. A very common setup to which I added an ITPS (power regulator and sequensor) . I am going to take my laptop in there and investigate the interference with that running. I will let everyone know what I find as it may come in handy to others with the same mod.

I wonder if other MO owners with carputers have run into the same issue. Perhaps not because most carputers are designed to shutdown with the ignition switch off. I modified mine to let me decide if I wanted it on at all times, off at all times, or bootup and shutdown with the engine. Without this mod I would not have discovered this interference issue as there are none when the PC is off!
 

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Mr. 3 K, 3/3/5. 5K,10/5/7
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Do you have any inverters running? Do you have a scope to look at the line for noise. Radio shack also makes filter sets, and a simple capacitor between the lines and Ground may also drainoff all the ripple and AC components floating on the line. It's probably radation from all this stuff overwhelming the relatively weak "wanted signals" sometimes it takes a while to find it.

Would be nice if you don't have to, but you may have to shut it down, Who know might be a fire or other kind of hazard to leave it on anyway. Rots of Ruck. :D
 

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Discussion Starter #16
No inverter. I did not like the step-up and step-down idea, plus I'd heard inverters create noise on the screen. Power is direct from battery to ITPS and then to PC power supply. I have a feed from the power supply back to the monitor. I also connected a wire from ignition source to the ITPS (for ignition switch mode detection) which I can bypass via another switch. GPS is powered via the PC. For "always on" mode, there is only one connection to the car, and that is to the battery. I take that back, I also have the ground wire!
When I get home tonight, I will get a couple of Ferrites and put on the power lines. If that does not work, I will disconnect and relocate the gps receiver and if that does not solve the problem then I will just give up on the idea of having the pc on while engine is off. It is just good to have that option if you are temporarily leaving the car and you do not want to go through the shutdown and bootup sequence (which is hard on the hardware)
 

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Last thought, You might like the power wire to the battery to be shielded between the ferrite and the battery and mount the ferrit as close to the carputer as possible. :D
 

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Ahh... A little late to the table, sorry guys. The title didn't draw me in.

Definately Don's on the right track. When the PC's on, there's a heap of things trying to radiate RF energy. The Key Fob and Receiver are not well filtered, so any energy around 310-320 MHz or around there, if significant, will hammer the front end of the receiver and "desense" it. This desensitization is a result of the front end of the receiver being saturated with RF energy, while it tries to "hear" your remote. To compare it, think of someone yelling at you, while you try to hold a normal conversation with another partner. (For many guys, you could think of your wife yelling at you to do things around the house, while you're on the phone trying to set up the next Golf time with your buddy. Sorry, couldn't resist...)

So how do you stop the yelling? Well look for leaks.. On the PC case, make sure there are metal to metal contacts on the various parts of the case. Any wire that exits the case is potentially a transmitting antenna. Snap on ferrite chokes, like Don mentioned, help. If you can loop a wire through it more than once, do it. You may also need a few of them to quiet things.

If you really know what you are doing, it's possible to put on some bypass capacitors in strategic areas.

Ideally, the whole thing is easier with a spectrum analyser, but if you don't have one of those (who does, right?) you can tune for strong signals with a radio scanner. You know, the one collecting dust next to your CB. Look for things in the 300 to 330 MHz range. Find the strong ones, and then watch what happens with the various things you put chokes on, or disconnect.

Also, if your motherboard supports a spread spectrum clock, turn it on. It will spread the oscillator energy and reduce the higher levels of interference.

That's what comes to mind off the top of my head....:D
 

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jaak...

:6: ...
 

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Discussion Starter #20
Thank you for all your good advice, and jaak for your expert input on the reasons for the problem. Unfortunately I am not well versed in electronic stuff so I have to forget about bypass capasitors or the spectrum analyser. The only thing I will be able to do is to get a bunch of ferrites and hang them on the wires sticking out of the PC. For the potential number of ferrirte i will need Radio shack is too expensive ($6 + tax each) I will try fry's tomorrow if they are open! I will let you know how it worked.
 
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