OT: Problems with Dart Tag!

[Bob Eager]

I have a Dart Tag fitted in my car. This is one of those devices that allows you to prepay toll charges, then have the barrier open automatically (and the account debited) when your car drives up to the toll booth.

I have a new car, and the tag no longer works. The windscreen is heated and laminated, but then so was the old one (same car manufacturer). The guy at the toll booth said it was because the screen is 'laminated'; I find this hard to believe, but then...

Round the edge of the glass is an area made up of small dark dots. This area is a few cm deep at the top centre on the screen, and stretches down to the mirror mounting (it's one of those all singing, all dancing rear view mirrors). I assume that the dotted area is unheated, so might be a better place to stick the tag. However, I'm worried because the dots are slightly rough and I'm not sure what they do.

Any explanation/comments would be welcomed! Thanks...

[John Kenyon]

The DART Tag website is crap, however, from the "EZPASSnj" website:

"Windshields with solar ray glass, solar tint, heated or heat reflective windshields, and insulated or Insta-Clear glass may also prevent the tag from being read properly. Customers with these windshields might need to obtain exterior tags. If you are unsure about whether your vehicle has one of the mentioned features, contact the dealer where you purchased your car."

EZPass uses the same type of technology as the Dart Tag, incase you were wondering

Try looking for an area of windscreen which isn't heated, and mount the tag there, or see if DartTag do "external tags" - in the US these are mounted behind the number plate. If they don't do external tags, then try mounting the tag in a plastic bag behind the radiator grill, and only use lanes which allow both cash & tag until you've confirmed the thing works OK.

/john

[Peter Parry]

It's a load of horsefeathers. There would easily have been differences in RF characteristics between the two windscreens though. Dart uses SAAB PREMID system operating on 2.45 GHz and at that frequency a thin metal film on a screen is as good as a sheet of steel but you can get all sorts of odd reflections which would have let a signal out.

The dots are simply decorative baked on paint to hide the joint to the bodywork. There should be a cutout in the heated screen for fitting a mobile phone antenna coupler. These are usually at the screen top centre immediately in front of the mirror and sometimes on the lower nearside corner. If you look at the screen at a sharp angle you can sometimes spot the slight change of colour. They may also be described in the car handbook if it mentions fitting mobile phones.

Either of these places should work OK for a Dart Tag as long as its maximum reader range of about 5m is not exceeded.

[Peter Parry]

Only in a relatively broad sense that both are RFID systems. EZpass uses 915MHz, Dart uses 2.45GHz and the Kapsch (SAAB Combitech Traffic Systems) PREMID TS3000 system.

At 2.4GHz I'd be very surprised if this did anything other than get the tag dirty.

[The Medway Handyman]

I had the same problem Bob. The area you describe is meant for things like Dart Tags & the like. Don't know exactly why, but they do work if placed in that area.

[Bob Eager]

Thanks...will do! I had a look, and the glass is not the 'solar' type (unless I got that as an unpaid 'option'). So it must be the heating element, and there are no significant gaps in it anywhere. Apart from in that area, no doubt, but that';s obscured by the 'dots'.

[Owain]

According to a QVC demonstration of a GPS system, the new form of demisting heating element in the glass also blocks GPS reception so an external antenna has to be used.

Does the tag have to be on the front windscreen - would it work on a door window (provided Bob remembers not to wind the door window down and it fall off)?

Owain

[Terry]

I used to have a Ford Focus with heated windscreen but with the Dart Tag fixed directly behind the rear view mirror, I never had a problem.

Perhaps you just have to find the correct place?

Terry

[Bob Eager]

Well, yes. Looks as if that's the area I was afraid to put it on...!

[Bob Eager]

Pretty sure it has to face the front. I'll try the area suggested and see what happens.