I've got an existing guitar effects pedal that has an excruciatingly bright clear blue PCB mount LED. It indicates when the pedal state is on or off. It is just waaaaaaaaaaaaaay too bright and makes it nearly impossible to look at the controls and make adjustments. There is an existing resistor that I'd like to replace with a higher resistance to decrease the brightness.
Let me share what I do understand so far as being necessary to determine the desired resistor:
1. Need the forward volts of the LED
2. Need the preferred current of the LED during operation
3. Need the volts supplied to the LED
From testing the circuit, the input volts to the 5mm blue LED is roughly 8 volts -- which makes sense since it operates using a standard 9v dry cell battery. The drop across the LED is about 2.8 volts -- that sounds about right for a 5mm blue LED too. I'm guessing that for a 5mm LED the current should probably be somewhere in the ballpark of 20 mA. The question I have is that I don't understand the use of the existing resistor based on what I think I've read as its value -- 11 ohms (see attached picture). Based on the above numbers I arrive at a much different value that should probably be used -- 260 ohms or so -- to get the current in the ballpark of 20 mA with this particular LED. I'd like to understand the existing resistor value to try and determine a better value to use as a replacement and achieve a much dimmer LED.
I would be extremely grateful if someone could double check my math above and also the reading of the existing resistor value.
Also, just FYI, looking at the image, the LED is mounted to the opposite side of the board with the positive leg attached to the left-most solder joint above the resistor. Power flows through the LED from a circuit trace on the other side, to and through the resistor, and to ground.
Thanks so much!
Steve
Let me share what I do understand so far as being necessary to determine the desired resistor:
1. Need the forward volts of the LED
2. Need the preferred current of the LED during operation
3. Need the volts supplied to the LED
From testing the circuit, the input volts to the 5mm blue LED is roughly 8 volts -- which makes sense since it operates using a standard 9v dry cell battery. The drop across the LED is about 2.8 volts -- that sounds about right for a 5mm blue LED too. I'm guessing that for a 5mm LED the current should probably be somewhere in the ballpark of 20 mA. The question I have is that I don't understand the use of the existing resistor based on what I think I've read as its value -- 11 ohms (see attached picture). Based on the above numbers I arrive at a much different value that should probably be used -- 260 ohms or so -- to get the current in the ballpark of 20 mA with this particular LED. I'd like to understand the existing resistor value to try and determine a better value to use as a replacement and achieve a much dimmer LED.
I would be extremely grateful if someone could double check my math above and also the reading of the existing resistor value.
Also, just FYI, looking at the image, the LED is mounted to the opposite side of the board with the positive leg attached to the left-most solder joint above the resistor. Power flows through the LED from a circuit trace on the other side, to and through the resistor, and to ground.
Thanks so much!
Steve