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opto isolator circuit help

all i need to know is the appropriate value for the resistor labeled unknown value and the right pins for the moc3021
 

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davenn

Moderator
what are you trying to do ??
the circuit isnt wired correctly as laid out so far

one side of the LED in the opto coupler should go to 0V rail
the other side should go to the signal via an appropriate resistor.
at the moment you have 2 resistored leads going to the opto-coupler
that isnt correct

Dave
 

davenn

Moderator
OK found the datasheet for it
this is the pinout....

attachment.php



so pin 2 goes to ground, pin 1 goes to your signal via a resistor
The LED's in opto-couplers are reasonably standard ones so
use a ~ 20mA as a max current through the LED, work out the resistance needed
considering the voltage from your signal source ( that transistor to the right ????)

Again PLEASE describe exactly what you are trying to achieve


EDIT .... just realised the signal source is the Arduino so are you trying to use it and the opto to switch the power on and off from the plughpack ? You still need to consider the output from the Arduino and if it is going to supply the LED with excess current .... I dont know anything much about Arduinos

Dave
 

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i think the leds not going to be a problem its hooked up to my arduino wich is hooked to my computer i have gotten it to work before with this schematic i will upload it soon

but i want to isolate the circuit so i dont blow up my expensive laptop and/or arduino mega

the reson i posted it here is becouse i need help with the wireing on the other side pins 4 and 6 the arduino hook up is fine
 
the point is for christmas light controll through vixen (vixenlights.com) my arduino is programmed perfectly
and works i just need something like an ssr but with a mosfet irf640 or another cheap one with at least 8A and 120v and works with pwm i already have an irf 640 so i hope to stay with that one
 

davenn

Moderator
OK you didnt answer my Q ....
so are you trying to use it and the opto to switch the power on and off from the plughpack ?

and what is that device to the right ??

Dave
 
i have bought dc ssrs before but the ones that work withh pwm is out of my price range
40 dollers heck no ill blow up mechanicals before going to that price
 
it is controlling christmas lights on the out put the ac is converted to dc at the begining the irf640 is the switch obviasely and it is controlled by an arduino and opto isolator
 
oh and the 470 ohm is a pull down resistor so the irf 640 doest get damage when off learned the hard way with ten test circuits
 
heres my test circuit again the resistor is a pull down incase the coommon ground gets pulled
 

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(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Your circuit is extremely dangerous, the Arduino is going to be at mains potential.

Stick to SSRs, It will be harder to electrocute yourself.
 
the first image i put up is the one i want to use but i need to know what resistor value is needed for bringing the 120 down to the 5 to 20 volt range
 
technecally i want the circuit in post 10 except with an opto isolator in it between the arduio and te rest of the cuircuit arduino used as output not input
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
And that's what you've shown in post #13.

You need a resistor in series with the LED in the optocoupler and the MOC3021 will provide example circuits for controlling the triac.
 
need help finding right resistor

all i need to know is the proper value for R1 the gate voltage on the irf640 is 5 - 20 volts 20 volts MAX input voltage is 110 vdc not ac
 

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(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
See here. They give resistor values for 110V and 220V

Why do you want t use a mosfet? Do you want to be able to turn the load off mid way through a half-cycle?
 
See here. They give resistor values for 110V and 220V

Why do you want t use a mosfet? Do you want to be able to turn the load off mid way through a half-cycle?


thank you, for your reply so i just need to use a 2.7 k ohm resistor for the gate on my irf640 for a 5 volt trigger and yes i am using this as a dimmer via pwm for a christmas light show that is why the circuit is dc instead of ac being converted to dc via
pRS1C-2160493w345.jpg

http://www.radioshack.com/product/index.jsp?productId=2062583
yes i am aware that it will turn on when the opto isolator is off and off when the opto isolator is on in my schematic
 

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