Hi,
im new to the electronics side, but i have a 12v input from a laser trigger via a relay and need to output 3.3v. I've seen somewhere else that i need a 470 ohms resistor (colour band Yellow Violet Brown Gold) they have turned up today and the 12.24v in and the other side of the resistor is still 12.24v?
so it basically appears to have no effect at all. should i be using something else to instead of or as well as to get the voltage down to 3.3?
thanks
You need a voltage regulator module.
brilliant, thanks.
will try find one from a UK supplier 
If you do not need your circuit to supply much current, then you could use a simple voltage divider.
Is the 3.3V just needed for a logic level input (in which case a voltage divider will suffice), or are you using it to power something? (if that is the case, then jremington's solution would be preferable).
bowen73:
Hi,im new to the electronics side, but i have a 12v input from a laser trigger via a relay and need to output 3.3v. I've seen somewhere else that i need a 470 ohms resistor (colour band Yellow Violet Brown Gold) they have turned up today and the 12.24v in and the other side of the resistor is still 12.24v?
so it basically appears to have no effect at all. should i be using something else to instead of or as well as to get the voltage down to 3.3?
thanks
You could use a 10k resistor to directly connect to an input pin, the 10k is probably enough resistance to
limit the protection-diode current on the pin to a safe level, else use a 10k/3k3 divider (about 1/4)
Def dont use a resistor between 12v and an input pin rated for only 3.3 or 5v....sure it limits current but what youre really doing is pull an input pin up to a 12v rail which would most likely break something!!! Divider or regulator is the way to go depending why youre needing the 3.3
dcrash36:
what youre really doing is pull an input pin up to a 12v rail which would most likely break something!!!
The input protection diodes clamp the input voltage to VCC+0.65volt, so no 12volt on the input.
This Atmel application document connects 230volt AC on an input pin through a current limiting resistor.
Leo..
What the guy needs it either (... question is not clear enough):
a voltage regulator (post #2 in this thread) - when he wants to supply a voltage to a circuit
a voltage divider using two resistors - when he wants to reduce the input voltage for an Arduino input pin
Who ever talked about 230 Volts?? And when you follow the link, you will end up with a discription of a Zero-Crossing-Detection device.
arduinoaleman:
Who ever talked about 230 Volts?? And when you follow the link, you will end up with a discription of a Zero-Crossing-Detection device.
I think he was using it to make the point that you can put a much larger voltage on an input pin without damaging it.
If you want to pull much current at 3.3V from 12V, get a 90+% efficient DC-DC buck converter rated for twice what you want. A 3A output adjustable might cost about $2 on eBay. More amps, more cost.