cellphone switching a 12 volt relay?

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jnash

Member - Posts: 5

Joined: June 30, 2004

Location: United Kingdom

Posted: May 01, 2007 at 9:11 AM / IP Logged

i want to use my phone to flick on a relay in my car, however hot sure how to go about it and also becasue a mobile only outputs 3.6 volts, any idea! thanks

KPierson

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This member consistently provides reliable information

Joined: April 14, 2005

Location: Ohio, United States

Posted: May 01, 2007 at 10:20 AM / IP Logged

Run the 3.6vdc output to a NPN transistor (like a 2N3904).

The cell phone output would connect to the transistor base through a ~220ohm resistor.

The emitter of the transistor would connect to ground

The collector would drive your relay, WITH a coil across the coil.

Thats the hardware solution, now getting your cell phone to output that signal when you want it to is up to you!

Kevin Pierson

jnash

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Joined: June 30, 2004

Location: United Kingdom

Posted: May 02, 2007 at 5:18 AM / IP Logged

thanks, im extremely new to the whole electronics idea, i was thinking that the output could come from the led's that light up the backlight or keypad, any thoughs on this.

im using the multimeter, but im not sure when dealiing with this for cellphones as opposed to 12 volt!

jnash

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Joined: June 30, 2004

Location: United Kingdom

Posted: May 02, 2007 at 5:25 AM / IP Logged

also, so would that mean the the collector is outputing 12 volts for the coil of the relay! and ground the other end!

KPierson

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Joined: April 14, 2005

Location: Ohio, United States

Posted: May 02, 2007 at 6:27 AM / IP Logged

No, the collecotor will output a (-) signal. The other end of the relay must be tied to 12vdc

Kevin Pierson

jnash

Member - Posts: 5

Joined: June 30, 2004

Location: United Kingdom

Posted: May 02, 2007 at 12:20 PM / IP Logged

thank you, just getting the parts but what do you mean

WITH a coil across the coil.

im assuming you mean the wire with the coil on it?

thanks

jnash

Member - Posts: 5

Joined: June 30, 2004

Location: United Kingdom

Posted: May 02, 2007 at 1:56 PM / IP Logged

found my output its 17.8 when setting the range on multimeter to 200m on DCV setting , wil this work stilling useing what you said above, thanks

JOn

KPierson

Platinum - Posts: 3,527

Joined: April 14, 2005

Location: Ohio, United States

Posted: May 02, 2007 at 3:09 PM / IP Logged

I meant a diode across the coil, not a coil across the coil, sorry.

17.8mV won't be enough voltage to turn on a transistor. You need at least 0.7vdc.

Kevin Pierson

sprint_dddddddd

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Joined: December 29, 2005

Location: United States

Posted: May 03, 2007 at 2:09 PM / IP Logged

Just an idea, not sure if it would help any; you might think about looking into some blue tooth and blue tooth components to help you send your signal from your phone to your wiring system. The Blue Tooth components may or may not work directly, but even if they dont you may find an indirect way to send the signal.

Out of curiosity, what exactly are you trying to control with your phone. I think what you are trying to do is pretty interesting.

Search for other posts by sprint_dddddddd

dualsport

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Joined: September 27, 2005

Location: United States

Posted: May 05, 2007 at 2:48 AM / IP Logged

You might want to check your voltage output again if you were measuring across the LED. There aren't any LEDs that would light up with only 17mV-

What were you using as the reference (-) side of the measurement?

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cellphone switching a 12 volt relay?

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