Dumb newbie resistance question
Ugha
Posts: 543
I feel like a total idiot.
I had a resistor I desoldered from a circuit board, meaning to reuse it or at least write down its value... but I lost it.
What really makes me feel stupid is the fact I can't figure out how to calculate the value of it.
I pretty much understand ohm's law, but I can't figure out how to use it to calculate what value the resistor was.
Can anyone give me a hand with the math?
The resistor was a current limiting resistor in series with two IR leds in an old mouse.
The original input value was 5 volts. The value seen by one of the LEDs was around 1.6volts.
If anyone can give me a hand figuring it out, i'd appreciate it. If not, can someone suggest a "safe" resistor value
that will most likely work?
I had a resistor I desoldered from a circuit board, meaning to reuse it or at least write down its value... but I lost it.
What really makes me feel stupid is the fact I can't figure out how to calculate the value of it.
I pretty much understand ohm's law, but I can't figure out how to use it to calculate what value the resistor was.
Can anyone give me a hand with the math?
The resistor was a current limiting resistor in series with two IR leds in an old mouse.
The original input value was 5 volts. The value seen by one of the LEDs was around 1.6volts.
If anyone can give me a hand figuring it out, i'd appreciate it. If not, can someone suggest a "safe" resistor value
that will most likely work?
Comments
http://www.csgnetwork.com/resistcolcalc.html
Also try this site as well for ohm law
http://ourworld.compuserve.com/homepages/Bill_Bowden/ohmslaw.htm
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Sam
With two LEDs in parallel, you have double the current. An LED typically takes up to 20mA, but that's pretty bright. Assume 10mA per LED = 20mA.
Ohms Law: R = V / A = 3.3V / 0.02A = 165 Ohms. A common standard value would be 150 Ohms.