What is the best way to find out what resister i would need to take a 6v down to 1.25 so i don't burn up the led light. Also how do you find this out so i know for future projects. A formula or web page for be nice to have if its to hard to explain
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Good question
We know the led cannot deal with more than 1.25 volts, but we don't know at least one other key item. We don't know the maximum current rating of the led and we don't know the impedance or resistance to current flow created by the led. If your led came with one of these, (usually Imax or maximim current) use that to calculate your resister in this formula
V=IR
where V is voltage
I is current (cannot be larger than Imax)
and R is resistance
so R=V/I
as we're just dealing with the resister now we have to subtract out the voltage across the led.
R = (6-1.25)/Imax
If you don't have this information then we can guess or experiment.
A 1K resister is a good starting place, but if you want to have a little experimental fun you can wire up your led in series with a 1 meg potentiometer (1 million ohms). Make sure the resistance on the potentiometer is set to maximum before you attach the power supply. Once your circuit is flowing current, slowly turn the potentiometer resistence down until the led glows at a comfortable level. You can even put a volt meter across the led to verify that you don't exceed the 1.25 volts.
Once you have the pot tuned to where you would like the resistance to be, disconnect the voltage supply and measure the resulting resistance with an ohmmeter. Get your fixed resister as near to the measured potentiometer reading as you can. If you have to make a choice, choose the higher resistance.
Have fun
I've attached an easy to read site that may help.
We know the led cannot deal with more than 1.25 volts, but we don't know at least one other key item. We don't know the maximum current rating of the led and we don't know the impedance or resistance to current flow created by the led. If your led came with one of these, (usually Imax or maximim current) use that to calculate your resister in this formula
V=IR
where V is voltage
I is current (cannot be larger than Imax)
and R is resistance
so R=V/I
as we're just dealing with the resister now we have to subtract out the voltage across the led.
R = (6-1.25)/Imax
If you don't have this information then we can guess or experiment.
A 1K resister is a good starting place, but if you want to have a little experimental fun you can wire up your led in series with a 1 meg potentiometer (1 million ohms). Make sure the resistance on the potentiometer is set to maximum before you attach the power supply. Once your circuit is flowing current, slowly turn the potentiometer resistence down until the led glows at a comfortable level. You can even put a volt meter across the led to verify that you don't exceed the 1.25 volts.
Once you have the pot tuned to where you would like the resistance to be, disconnect the voltage supply and measure the resulting resistance with an ohmmeter. Get your fixed resister as near to the measured potentiometer reading as you can. If you have to make a choice, choose the higher resistance.
Have fun
I've attached an easy to read site that may help.
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You need to know the voltage drop across the LED, which is normally about 1.75 volts and current which is usually about 15 milliamps
The resistor must drop 4.25 volts = (6 - 1.75) with a current of 0.015 amps.
Use ohm's law R = (V battery - V LED)/ I LED
R = (6 -1.75)/0.015 = 283 ohms, this is a non standard value use a 300 ohm resistor, it should be a 1/4 watt
The resistor must drop 4.25 volts = (6 - 1.75) with a current of 0.015 amps.
Use ohm's law R = (V battery - V LED)/ I LED
R = (6 -1.75)/0.015 = 283 ohms, this is a non standard value use a 300 ohm resistor, it should be a 1/4 watt
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LED NEVER HAS 1.25V RATE.
The first generation RED LED is 1.6V , A few years later the Green and Yellow is 1.8V to 2V. White LED needs even higher 2.7V to 3.2V.
If your calculation use 1.25V , any LED never being able to light up.
The first generation RED LED is 1.6V , A few years later the Green and Yellow is 1.8V to 2V. White LED needs even higher 2.7V to 3.2V.
If your calculation use 1.25V , any LED never being able to light up.