# switching using a 4n 25

Discussion in 'General Electronics Chat' started by jonisonvespa, Dec 31, 2012.

1. ### jonisonvespa Thread Starter Member

Mar 25, 2012
49
0
hi
im trying to switch a +5 to a pin on a auduino project, the switch circuit is in a very noisy environment hence i using an opto isolator, first time ive used one

have i got my circuit correct? ive limited both led and current to the ic pin to 10ma

thank you

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2. ### ramancini8 Member

Jul 18, 2012
447
119
You don't have the circuits seperated, so the opto doesn't accomplish much.

3. ### #12 Expert

Nov 30, 2010
16,671
7,314
The way you have that laid out, the "+5 volt to pin" is always at +5 volts. I think you need to move the 560r to the top of the transistor, not the bottom.

The result would be a reversal of the logic. If this is not good, explain your wishes better and we can work something out.

4. ### jonisonvespa Thread Starter Member

Mar 25, 2012
49
0
ok i think ive got it now ive revised my circuit

just wondering if there is any way i could use the + and gnd in my circuit, for the (opto part switch)

and isolate that from the rest of the circuit?

thank you

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Last edited: Dec 31, 2012
5. ### #12 Expert

Nov 30, 2010
16,671
7,314
That will work.

6. ### KrisBlueNZ Member

Oct 17, 2012
111
14
I'd suggest increasing the pullup resistor on the collector. A 560 ohm resistor will draw nearly 10 mA from the 5V rail when the optocoupler is activated, which is a bit wasteful. A more typical value would be 10k.

If you want to interface to an electrically noisy environment, I would suggest using series resistors of 1~10k in both of the wires that go out to the switch (which I assume is in the noisy environment) and a capacitor of say 10~100 nF from the microcontroller input to ground. You will lose the electrical isolation, so there's no reason to use an optocoupler.