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Author Topic: Automatic power switch  (Read 452 times)
WS4E
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Posts: 199




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« on: March 27, 2010, 07:47:28 AM »

I have my VHF mobile connected directly to the battery so it has power all the time and has to be manually turned on and off.  

Does anyone know of a simple circuit that would use one of the switched power lines to watch if the car is on and then turn the radio on?

I was actually thinking this migh be as simple as a reed switch or something and using the power line from the ignition to close the contacts.   Heck it might even be possible to use a 555 to add a short on off delay.

I was just,wondering if anyone had done anything like that before.

Thx
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K0BG
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Posts: 9834


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« Reply #1 on: March 27, 2010, 10:30:17 AM »

This is what you need: http://www.powerwerx.com/west-mountain-radio/pwrguard-protects-the-radio.html
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W3LK
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Posts: 5644




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« Reply #2 on: March 27, 2010, 12:39:19 PM »

I have my VHF mobile connected directly to the battery so it has power all the time and has to be manually turned on and off.  

Does anyone know of a simple circuit that would use one of the switched power lines to watch if the car is on and then turn the radio on?

I was actually thinking this migh be as simple as a reed switch or something and using the power line from the ignition to close the contacts.   Heck it might even be possible to use a 555 to add a short on off delay.

I was just,wondering if anyone had done anything like that before.

Thx

Put a simple 12V auto relay in the line with the control line connected to a convenient switched terminal on the fuse panel. Probably about $10 and 20 minutes to install it. This was standard on commercial installations for years.
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A smoking section in a restaurant makes as much sense as a peeing section in a swimming pool.
AA4PB
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Posts: 12644




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« Reply #3 on: March 27, 2010, 01:41:35 PM »

Wire the automotive switch common and normally-open contacts in series with the DC power to the radio. Connect one side of the coil to ground and connect the other side (with an in-line 1A fuse) to the vehicle accessory circuit at the fuse block or at the AM/FM radio.

When the ignition is on or in the ACC position then the relay will close and power will be applied to the radio. Power will be removed just before the starter is engaged or when the key is in the off position.

Accessory power will be available at one side of one of the radio fuses in the fuse block. If you poke around with a voltmeter you can often find an extra (empty) fuse pin on the block nearby. You can remove a pin from an old blade fuse and use it for a connector. Worst case, if you can't find accessory power at the fuse block you can always tap into it at the AM/FM radio.
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K0BG
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« Reply #4 on: March 27, 2010, 02:14:36 PM »

I guess I should have asked what radio you have. Most of the new stuff have built-in auto off features.
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