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Topic: Arduino 5V output - Switch a device on/off with relay (Read 2214 times) previous topic - next topic

renasis

Hello,

I am running a camera that requires 5V 80-100mA. I can use the 5V output of arduino, no problem. I tried running from a digital pin(which I believe provides ~40mA), this does not work. So I tied 3 together to get my mA requirement. I rather not use all of these pins just to provide power to camera, can I put a relay on the 5V out instead?

Thanks,

-ren

Runaway Pancake

#1
Apr 10, 2012, 05:21 am Last Edit: Apr 10, 2012, 05:29 am by Runaway Pancake Reason: 1
Paralleling pins - Gasp!
Get a 5V reed relay, the one Radio Shack sells is just right, and its contacts are rated for 1/2A.
If you don't live in America, look for one with a coil resistance of 200? or so.  And.. you need that diode, too, [though some have that integral.]
Or - get a transistor.

* * * *
http://s270.photobucket.com/albums/jj118/new_clear_days/circuits/?action=view&current=OSRRdemo-1.mp4

http://arduino.cc/forum/index.php?action=dlattach;topic=77590.0;attach=8885;image
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"You gotta fight -- for your right -- to party!"
Don't react - Read.
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renasis


DuaneB

Read this
http://rcarduino.blogspot.com/2012/04/servo-problems-with-arduino-part-1.html
then watch this
http://rcarduino.blogspot.com/2012/04/servo-problems-part-2-demonstration.html

Rcarduino.blogspot.com

Runaway Pancake

Hey, renasis,
I just wanted to note that the pic was used in answer to another's question.  He was needing to trigger a camera into an active status.
But you want to switch power, so the contacts, being an SPST switch, would be placed between the supply/battery and "camera +Vin"
"Hello, I must be going..."
"You gotta fight -- for your right -- to party!"
Don't react - Read.
"Who is like unto the beast? who is able to make war with him?"

renasis

Hello,

Initially I was going to use the reed relay, but I happen to have a npn 3904 transistor, so I am going to give that a try. I will have a digital pin connected to the base. I can figure out the resistor needed to give me enough current Ib, to allow the current needed for the load(camera) Ic. I will put 5V to load(camera) to the collector of the transistor. I have seen some people online putting a diode(flyback) in parallel to the load to eliminate excess voltage. I understand that this is to protect against a voltage spike at the collector of the transistor. I probably don't need this in this case because this device will not build up a charge, but I am curious as how the value of the diode is determined if I decided to add. Also, in some instances online I have seen where a resistor placed between the load and the collector, why? If it requires too much explaining, could you point me to a reference to learn about this?

Thanks,

-ren

Runaway Pancake

The "backward" diode gets placed across the relay coil.  The coil, being it's a coil, has an inductance, it's an inductor, and inductors store a charge (hundreds of volts, for microseconds) - and they release that charge when they're de-energised.  The diode provides a low-resistance path for that charge (discharge).  That's it in a nutshell.
You don't have to sweat base resistor values for idealised collector current v. h_FE, etc. - anything 1K-5K? ought to get it good enough.
"Hello, I must be going..."
"You gotta fight -- for your right -- to party!"
Don't react - Read.
"Who is like unto the beast? who is able to make war with him?"

renasis

Runaway Pancake,

Thanks for the explanation about the diode. How do you chose the proper size of diode?

Thanks,

-ren

Runaway Pancake

"Hello, I must be going..."
"You gotta fight -- for your right -- to party!"
Don't react - Read.
"Who is like unto the beast? who is able to make war with him?"

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