12v relay connected to cell phone

i got some aftermarket fog lights, with wireless controller, they are cyberwhite ones.  the wireless controller controls a relay that turns on and off the lights.  that would be much wiser then using a cellphone and having to pay to use it everytime.

all the wireless relay setup is, a 2 button wireless remote (on/off)  then a box that is basically just a relay, with a little wire antenna, would be very simple to connect for what you need to do

I agree that this could most certainly be done for under $100. The quickest may just be your idea of 2 calls with specific timing. Do you already have the cell phone you plan on using?

Honestly If I were doing this I would probably just get a cheap phone that has a vibrator motor in the battery (do they still do it like that?) then just rip apart the battery. Then I would just program a microcontroller for the specific timing and hook it to the motor then use the output to drive a transistor and relay. Total cost would probably be around $10-$15 excluding the phone cost.....

Although it may be more elegant to get the phone and use a serial link and microcontroller (or PC) then just call and give a specific passcode type system on the keypad

good luck

I would just use an automotive relay (automotive forum lol) simply because they are cheap, handle 30A (or 40), and since you have a 12V system you can easily drive it. But I would drive this with a BJT (transistor), this way its cheap and will not draw the power a relay needs from the phone, plus cheap BJTs can be had at any radioshack or electronics store (like a 2n3904 or 2n2222) for like $1, you will also need a resistor for the base of the transistor, a 1K ohm will be fine...total cost: relay: ~$1, transistors (only sell packsof around 5): ~1, resistor,pack of a few: ~1, total ~$3

If you really wanna be non-invasive maybe you could get a cadmium sulfide cell (like used in those little light sensitive photo-eyes), or a small solar panel and make a little thing to set the phone right down on, that way it would detect the light from the screen and you dont need to do anything to the phone...

which idea? opening it up and going that way is just a resistor to the positive activated lead, to the base of the transistor, emitter of the transistor to ground and collector to relay, other relay coil lead to +12 with a diode across the coil.

for a light activated switch this is a very simple way to do it:

http://www.uoguelph.ca/~antoon/circ/actrelay.htm  (circuit on the left)

one thing you could do if you want to go with the timer and dual call idea is use a 555 timer in monostable mode, what this will do is start a timer when activated and stay on for a certain period of time. You could then use some latch circuitry so that you would have to call back in a certain period of time, just a general idea of an idea, I would just use a microcontroller that way I could just do all the light sensing and timing in one chip that costs about ~1

good luck