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### Topic: 12v Trigger? Newbie here. (Read 2732 times)previous topic - next topic

#### Startgroup

##### May 25, 2011, 01:36 am
Hello, this is my first experimentation after doing blinkie.

I purchased a RFID reader from ebay a while back, it was \$10 and came with 2 rfids and does not require a computer.

I have played wired it up to an led and have played with it getting it to turn on when the right rfid is shown. Basically if I show the right card, the led lights up, when I take the card down, it immediately shuts off, so there is no relay.

Can I hook this into Arduino? It is a 12v signal that comes out of the rfid.

Meaning, can I have this 12v signal, trigger arduino to do something like turn a servo or power an led?

Thank you,

Scott

#### dev_000

#1
##### May 25, 2011, 05:00 am
Yes, you can. Put a potential divider circuit to step down the 12V trigger to 5V or lesser and give it to an arduino...

#### Startgroup

#2
##### May 25, 2011, 10:04 pm
Thats great news! Awesome! Thank you for the response.

Any idea where I would look to figure out which resistors I should use in the potential?

#3
##### May 25, 2011, 10:43 pm
12V to R1 to R2 to ground.
Junction R1/R2 to arduino.

Vout = Vin * R2/(R1+R2)

Have R1 + R2 = ~20K
So R2=8.2K, R1=12K would get you in a workable range.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

#### Startgroup

#4
##### May 26, 2011, 05:58 pm
Wow, thank you thank you.

I am not that good at math so you just saved me. I will try this this weekend.

Thank you.

#### Startgroup

#5
##### Jun 01, 2011, 05:40 am
Well look at that. I was actually able to pull off part 1 of my project. My RFID keyless entry to my apartment without modifying the door, lock, or striker (I'm not allowed too) is now installed and working beautifully.

I just wanted to say thanks to those who helped me below. I wanted to quit and now that I see progress I am actually ordering another arduino to try more projects.