Printer Friendly Forum Posts - 12v relay connected to cell phone

Hello Gents:

We have wireless(for Internet) transmitter that every now and then the radios get stuck and it needs to be reset. All we need to do is unplug it and plug it back in. The main feed is 110 ac, but the actual system runs on 12vdc which we have set on deep cycle batts for UPS. So, here is my idea to make a remote reset device, any help you can provide will be greatly appreciated.

1) Get a cheap cell phone.
2) Gut it, and connect a relay to the ringer/vibrator, this way everytime the phone rings it will cut the power to the radios momentarily and reset them.
3) Connect the cell phone to the 12v system with a car adapter, this way it will always be charged.

The tipical method is to reset the radios via the network, the problem is that if the radios are not working, the network will not be working. There is no pager/beeper coverage in that neck of the woods and only some cell phone companies serve the area. Also, there is no landline phone service.

The biggest drawback to this is that everytime there is a "wrong number" call it will reset the system. We are willing to live with this. Ideally, to avoid false alarms the cut-off device would have some sort of delay so that it would cut the power off if it received two calls within 1, 2, or 3, etc minutes(whatever is easier).

Thanks
Chele

PS

I did read the 3.3->12v relay and that is what gave me this idea, I am just expanding the concept a bit.
chele

whoa.... wheres dyohn when you need him..... i dont understand what your building.....

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The idea is that when the cell phone rings, it will open the circuit(activate the relay), this will cause the radios(which at this point are stuck) and get going again. I do not need to log on to a computer on to a computer or anything fancy, just disrupt the power supply to the radios. This will just be a remote control to open the relay(s).

did you try it? some phones can be linked via rs232 and such and might be a little less invasive... but pulling it apart and going for the vibrating motor would probably work, just use a transistor BJT or MOSFET, infact depending on the system current draw you could possible just use the transistor without a relay...

Im kinda confused reading that though...

How far away can you be at most, when you want to trip the reset on your radios? If you aren't going to be more than 5 miles away, I would suggest using two GPRS radios at each end with different frequencies on each one. Only when both frequencies are "ringing" at the same time, you could trip your relay the way you already have. Chances of two strangers within 5 miles rining at the same time on two different frequencies is going to be near impossible. However if your tripping distance is more than 5 miles, you could use 2 cheap cellphones and have both connected to 2 separate relays with a timer on each one for lets say 30 seconds. That way you could dial the first number, that would set the first relay to be engaged for 30 seconds, while you make your second call to the second relay (within 30 seconds) and then both relays being in series would set the trip switch (which could be a third relay) to your system. That would even eliminate the wrong number issue.

Sorry fellows

It makes perfect sense to me:) I didn't mean to make it confusing. What can I do to clear it up? I have not tried it yet, I was curious as to whether this could be done or not. I am willing to scrap a cell phone so I'm not too concerned about the invasive part, besides, I would need some sort interface to the rs232 if I went that route. I'm strugling enough with just the relay thing. Also, I don't know enough to attempt it without some guidance!!

It will be a regular cell phone with its own number just like the one that you might have. The only difference is tha it will have a relay(?) connected to it so that it will interrupt momentarily the power to the radios and force them to reset. The transmiter is about 1 hour away. The beauty of a cell phone is that I could trigger it from anywhere by dialing the cell phone #. It would be great if I could avoid false alarms.

To avoid(or reduce) false alarms the cut-off device would wait for a second call within a certain time frame, 1,2,3 etc minutes. This would be nice, but not necessary.

So, here is my thought:
a) phone rings and hang up, no need to complete call.
b) starts timer.
c) gets second call(step "a") within 2(?) minutes
d) relay opens, cuts power to radios for 5(?) seconds
this will force the radios to reset.

if the phone does not ring(step "c") again within 2(?) minutes, the timer stops and nothing happens.

Steps "b & c" would be great as it would cut down on false alarms.

I hope this clears it somewhat and I'm not making it more confusing than it already is.

Thanks
Chele

actually I was thinking about this a little more, even though I am still confused as to the exact implication and if it could be done another way....

You could use a modem on the phone and that way can use a better system to activate and elimnate false triggers,

something like this: https://www.wirelessemporium.com/store/catalog/product/details.asp?itemid=2756

but I dont know how cheap you want it to be...? there are wireless modules that you just shove a sim card in and can control things by calling, but I think that would be overkill...

maybe just the ringing time interval thing would be the cheapest....

Thanks xetmes. To tell you the truth, even the srs32 is overkill. I don't need the radios to execute any commands, just their power disconected for 5 seconds or so. From what I have researched my best option would be to get one of those prepaid cell phones for about $40-80,(no contracts) low monthly fee(don't care about the minutes). So long as I get signal at the transmiter site I'm OK.

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

blingo, I think that might not suit wifi's purpose because he wants to be able to control this relay via remote (long distance). The wireless switch you have for the relay for your forlights is most probably a very short range, just a few feet or more but not work wirelessly from miles away.

well i believe it says its a quarter mile range, depending on antenna posistion,, so you can find your car in a parking lot, i was thinking he would be in the same place as the radio he needs to reset, just didnt want to get up and reset it

Thanks Blingo, Markcars is correct. A remote as the one you say has a couple hundred feet range, at best. I want to be able to do this from another state if I have to. Two of the repeaters are about an hour's drive for me and 2-1/2 hours for my brother. By the time you are 100' from the repeater, not much point for a remote control. They sell equipment similar to this(without the timer feature) that are connected to beepers, for several hundred dollars. The price itself is not the problem, there is NO PAGER coverage at the sites. I think this could be done for less than $100.

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

Hello Xetmes, let me brag about my knowledge, you just went over my head. I actually have a phone that I can use, Motorola 205, it does vibrate, it does ring(very loudly), and the screen lights up whenever it gets a call. The way I figured, I have three potential methods of connecting a relay to the phone. From what I understand, the phone's batt is 4.1-4.3v(the internal parts more than likely are lower voltage), the radios are on a 12v system. Install a relay in the +side of the radios feed, connect the other side of the relay to anything on the cellphone with enough power to trip the relay when it rings, RESULT === phone rings, trips relay, radios lose power momentarily(while phone rings), radios reset :):). Why all this trouble you ask? Murphy's las dictates that I will need to reset the radios at the least oportune moment.

The timer thing is over my head, for now. The info I am looking for, is what type of relay do I need? I know that if I go to Radio Shack, they are going to be more lost/ignorant the I am.

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...

Thanks Xetmes, that sounds resonable. Any Idea where I might find a sketch to something like you describe?

Any sugestions for the timer, or should take it just one step at a time?

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:

https://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

Hello Xtemes

Thanks, the site you sent me to has a lot of potential. There are a couple of designs that look promising. Thanks a lot for the info

Chele

Not to change the subject but you guys can make this work I was wondering is there away to take the same concept but change it a little bit, like make a alarm when set off make a call(from a pre-paid cellphone) to my cell, almost like a infinite range paging alarm...

wifi if you have not got something together for this yet shoot me an email. What you want to do sounds fairly easy. If you can live without the timer setup and want something real easy that you could hook up without any experience in electronics it can be done. If you are stuck on having the timers and dont feel confortable building one, with a diagram and a friend that can build it =) we can get you going. mikelin4@hotmail.com

Thanks for the offer. I found this https://www.apogeekits.com/remote_control_via_cell_phone.htm

This is enough to get me going. We already bought, assembled it, and tested it. It works almost as what I originally wanted, for now, it's more than good enough. I will investigate it some more. The apogeekit does not solve the false alarm issue, and that is something I really want. I do want to thank you.

Take care

Set the phone up to be on SILENT mode (no ring, no voltage) to all callers except your number. Your number make the phone ring (+volts) and therefore trip the relay.

Relay would be normally closed and when switched (ring ring) is +volts -- it would kill power to your loads - therefore rebooting.

Just a thought...

I think you are going about this the wrong way.

Purchase a control box which hooks up to the rs232 port on the server computer. These are common and can be purchased for under $100.

Set up a server side script for a delay of whatever amount of time. Next thing is for the script to check for connectivity. If the test is OK then go back to start a new delay time. If it fails have it send a signal to the RS232 box to open the relay for whatever amount of time, then a delay for the radio to reset, and finally restart the script

Typical Controller