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-   -   Cell phone interference w/ car computer? (http://www.diyaudio.com/forums/everything-else/222906-cell-phone-interference-w-car-computer.html)

Conrad Hoffman 5th November 2012 02:53 AM

Cell phone interference w/ car computer?
 
Understand I'm not a cell phone person! Can't stand the annoying things. I happened to bring one on a trip today in my POS 2004 Mazda3. When I got in the car the door locks all clattered at the same time, twice for several seconds. Later I made a call and the dome light wouldn't respond to the switches and turn off anymore. Shutting off and restarting the car put everything right again. I know they affect computer audio systems and sometimes video, but has anybody ever seen anything like this? Random chance problem or was it really the cell phone getting involved with the alarm or computer system?

theAnonymous1 5th November 2012 03:01 AM

Never heard of such a thing myself. What type of phone is it, CDMA or GSM?

I guess to be certain, try and duplicate the incident?

marce 5th November 2012 09:23 AM

There have been similar problems in the past:
EMCIA - EMC Industry Association, Products and Members
Have a look at past "Bannana skins" section of the EMC club siteif yoiu get chance, some of the problems caused by EMI are worrying and in some cases humourous. But it is an increasing problem and one which in general is often overlooked on DIY sites.
Thisiswhy mobiles have to be switched off when near sensitive medical equipement and during take of and landing on planes.
imaginewhat problems an EMCevent could causewhen your coming in to land..

tubelab.com 5th November 2012 02:04 PM

I have about 5 years of experience designing cell phones, about 10 years ago. I have always been concerned with cell phones and electronics for reasons other than my job. I build loud guitar amps!

Cell phones operate on several different non compatible standards called "MA's". MA stands for multiple access, a means for several simultaneous conversations on a single radio channel. Most 3G and 4G (3rd and 4th generation technology) MA's use continuous transmission, the radio transmitter runs continuously all the time the phone is sending data.

Some 2G and 3G MA's use TDMA (Time Division Multiple Access) to allow multiple access. The voice is digitized and the data is packetized. The base station will allow the phone to use one or more time slots on a given radio channel, which is divided up into small parcels of time that are dynamically assigned to each concurrent user. The radio transmitter is switched on during its time slot and off during the transmit time for other users at a rate from 16 to 66 mS depending on the MA.

Phones using this pulsed transmission mode are the ones most likely to cause interference with electronic devices, and the fast rising RF edges are what you hear in your cheap PC speakers. The usual offenders are GSM, iDEN, EDGE, and variants of these, since they all use TDMA. GSM is the most popular MA in the world, but all of these MA are slowly being replaced with 3G and 4G systems.

I admit to having fun in some of the big box electronics and music stores by taking a phone, cranking its RF power up to max and going into the home theater room or the hands on guitar amp room. Some electronics are succeptable to RF from cell phones, and some isn't. The low priced stuff like cheap PC speakers are usually bad, but there are some surprises. A $7000 Yamaha digital grand piano went absolutely bonkers whenever I got within a few feet of it.

When cars started getting "drive by wire" throttle control I was skeptical, but I have been unable to cause any anomalies in several cars even when a "worse case" phone was placed on the "brain box" or ran all over the sensors and actuators under the hood.

It is possible that the phone caused the anomalies that you observed, but there would likely be a secondary cause. Usually it is caused by a repair tech not reinstalling all the shielding, and grounding features originally installed in the car.

I built a hot rod Dodge back in the 80's, installing a turbo charged engine using early (1984) digital engine control into a car that was originally carbureted. I left out a lot of stuff I didn't absolutely need and made my own wiring harness from scratch. Yes, it was possible to stall that car with an iDEN phone next to the unshielded brain box board.

Conrad Hoffman 5th November 2012 03:17 PM

Very interesting. Drive-by-wire scares the $hit out of me. I want my critical controls mechanically connected to the things they operate!

DF96 5th November 2012 03:55 PM

Were any of the car electrics made in China? If so, some of the EMC compliance components may have been omitted in the factory; I can't believe that it is only SMPS which get this treatment.

marce 5th November 2012 04:05 PM

Nope, and sometimesimported products dont measure up very well, even withthe CE mark on them...

Conrad Hoffman 5th November 2012 04:30 PM

Well, false alarm. The Mazda3 is still a POS and it did it again this morning with no cell phone present. Just failing electronics I guess, or maybe something related to the cold.

I should qualify my comments in that the intro year of the Mazda3 was a POS, but the later ones seem better. Most unreliable and expensive to own car I've ever had in 38 years of driving.

DF96 5th November 2012 05:15 PM

In the UK we always found it difficult to take Mazda cars seriously, because to most people Mazda is a brand of light bulb. Older folk may remember Mazda radio valves too.

marce 5th November 2012 05:28 PM

Try a Citroen C3, gearbox disintegrated, ECU gone duff, clutch, heater, brake calipers , two springs and a few other things in the last 8 months...spent more time in the garage than on the road recently. As to the elctronics, got a load of controls on the steering wheel, great fun, we have a lottery now on what will happen when a button is pressed, my favorite is volume up, it operates the rear wiper:)
P>S> it is for sale if anyone interested (well when I get a new ECU)


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