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Stopping the car aerial

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pieman54

New Member
Hi.......I've installed an electric aerial into my car (the original ford one) and am using 2 SPDT relays to reverse the motor (up/down). So with the radio off the antenna goes down and with the radio on the antenna goes up. I'm using the original car switch to do this. However, when the aerial fully extends or retracts I have to hit the switch to cut power to the unit otherwise the motor keeps running (not nice!!). So the question is what should I use to automatically turn power off to the antenna at full height or when retracted????? This function is normally controlled by the high series BCM (Body Control Module) - my car has the mid series.:)
 

Sceadwian

Banned
There has to be some mechanical or electrical feature built into the antenna to detect when it's retracted or collapsed? Small switches maybe with a detention on the antenna that would trip it when it's up or down. Unless the computer detected current from the motor and stopped when it was stalled. There's not really enough information to help you other than saying that. Current sensing the motor for stall should be pretty straight forward, the current is going to go way up.
 

Andy1845c

Active Member
Having the computer detect a stall via current seems very odd and way too exotic for automotive use to me.

Most power antennas I have worked with have limit switches and up/down circuitry built into them. I don't know if I have ever worked with a Ford one, but I think the GM cars had a single wire that controlled the antenna, when power is applied to it, it goes up and when power is removed it goes back down.
 

Sceadwian

Banned
Exotic? Current sensing is hardly exotic.
 

Andy1845c

Active Member
Just seems like an unusual way to design something like a power antenna. Certinly could be done and certinly would work, but limit switches seem more likely to me.

How old is this car/antenna? Most of the stuff I have worked on is a tad old. Maybe the newer cars use high tect solutions for goofy problems like that.:)

One thing about a current sensing design would be you would have the motor physically ramming the stops and stressing everything. With limit switches you could stop the mechinism before it got to the end of its travel.

On the other hand, limit switches add more parts and are probably more expensive then an integrated current sense circuit.

I guess they probably went with whatever got them just past the warrenty period. :D
 
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3v0

Coop Build Coordinator
Forum Supporter
I have not looked at one it years.

Some of them remembered how far you had the antenna extended. You could adjust the antenna up and down while the radio was on. When you turned it on the next time it extended to that position.

That can not be done with current sense or limit switches.
 

Andy1845c

Active Member
What would be the use of having it part way up? I haven't seen one like that yet. The ones I have seen (GM and Cadillac) just go all the way up or all the way down depending on if the radio is on or off. Its all kind of a gimmic if you ask me. Just more moving parts to break.
 

3v0

Coop Build Coordinator
Forum Supporter
Gimmic yes, like about 3/4 of the electronics on a new car.
I think the idea is reception varies based on the extension.
Maybe it was one of Ford's better ideas.

3v0

What would be the use of having it part way up? I haven't seen one like that yet. The ones I have seen (GM and Cadillac) just go all the way up or all the way down depending on if the radio is on or off. Its all kind of a gimmic if you ask me. Just more moving parts to break.
 

tcmtech

Banned
Most Helpful Member
I have had the doors apart on several Ford vehicals my family has owned and the power window controls I have seen that have the automatic one touch down function just stall the motor and then stop. They dont have any limit switchs or sensors to detect when its all the way down or not.
I am rather sure my power antenna works the same way too!

Try runing yours down at night while the interior light is on. I bet most of you will see the light dim for a second when the window or power antenna hits bottom!

My car broke the window control cable and if you hit the button for the auto down the motor would just keep on going even if I pushed the window all the way down by hand. I would have to push the button again to actualy get it to stop.

As far as stalling the motor to use current sensing, its a great way to get a regular cash flow for the dealers! Make it cheap, fragile and self distructive. Then charge a pile for a new one plus a high labor to replace it! :mad:

But its not like you guys have never seen that design used before!
 
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pieman54

New Member
More info

Thanks everyone for your comments. I've attached a quick diagram of the circuit so far.

And more information is......the car is a 98 Ford EL Futura, the aerial does not have any limit switches for up/down, the shut off is controlled by the BCM but I don't know if that is achieved via a timing circuit of a current sensing circuit. TCMTECH is right about the fords and no limit switches......what a legend!!!

So I guess from your comments the best way to go is to use a current sensing method. Does anyone have or know of one that would suit ???? And where in my circuit would I connect it???

Again thanks for your inputs so far.
 

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