Using arduino as a on/off switch for another 5volt system.

Hello. im building a arduino project that includes a "revolving light". this light is 5 volt also, my main idea was to run it off the arduino directly but the was not enough power for that.. So i thought of using a 4N35(optocoupler) but i cant get that to work at all. My connections are more or less identical to this (http://fritzing.org/media/projects/o/p/t/optocoupler/images/IMG_1892.JPG) (no that is not mine!) but its the same scematics. the battery and led is oufcourse a 5v source and a revolving light in my system.

Now, i have noticed that i cant start the revolving light if I put in a resistor instead of this ider. And if use my voltage meter to check the 4N35 has some hundred ohms resistance so thats probably my problem.

anyone who have an idea of a different way to solve this for me?

How many amps / milliamps does you light need?

I would expect the optocoupler to have much the same current limits as the Arduino - but the in and the out are electrically separate.

As everything is operating at low voltage an optocoupler is hardly necessary. The simplest way to make the Arduino control a bigger current is with a transistor. I'm sure there are many examples of suitable circuits.

There should be nothing to stop you driving the transistor with the output of th optocoupler if you want to keep it.

...R

My connections are more or less identical to this

Which: more identical, less identical, or identically identical? I'm not being funny: you really should post your actual schematic, and probably the code.

It is the same with this modifications. the led is a revolving light that needs 5v and an unknown amount of amps.(enough to drive it on usb thou, so not that much) the battery is a 5v source with 1000mA that is enough for the revolving light with good marginal.

I will try with a transistor. i thought a transistor was a bad idea when i had currents that did not have the same "ground".

the arduino and the other part should be separated as im affraid the current of the revolving light part of the scematics could harm the arduino unit.

i thought a transistor was a bad idea when i had currents that did not have the same "ground".

All grounds in a circuit MUST be connected together.

jremington: All grounds in a circuit MUST be connected together.

Not when an optocoupler is used!

...R