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joinpobob · October 21st, 2009, 02:20 PM

Hi,

So I finished building a compressor pedal for a friend last night. It sounds great and seems to work well.

I housed it and hit the switch; the LED shined bright blue for about 5 seconds, sputtered and then shut off. I just kept playing for a while and it came on intermittently.

I then opened her up and measured the voltages. I had 9.33V coming off of the DC power jack, 2.1V at the Anode, and 0V (ground) at the Cathode. I have a 1K Ohm resistor between the DC jack and the LED, which I guess has 7.2V across it. Does that sound right?

With everything still wired-up, I put a green led in parallel with the the blue LED (I just touched the leads together) and the green LED worked. I then put a blue LED in parallel with the original blue LED; in that configuration both turned-on worked for again about 5 seconds, sputtered and turned-off.

I didn't have the energy to get the soldering gun out and just wanted to play some more. When I went to play again, it turned on, sputtered and went off.

Any thoughts? Do blue LEDs need a bigger resistor (or a smaller one)?

Thanks!

CA_Dan · October 21st, 2009, 04:13 PM

From the StewMac website:

To calculate the correct size resistor, subtract the LED voltage from the battery voltage, then divide by the LED’s current consumption (in amps) to give the necessary resistance. For example, a red LED normally runs at 20 milliamps at 2.2 volts. If you use a 9-volt battery you have (9V - 2.2V) / 0.02 amps = 340 ohms. 100 to 330 ohm resistor usually work fine. Depending upon your calculations, you may want to choose a resistor a little smaller to account for the battery running down.

FenderLover · October 23rd, 2009, 01:33 PM

I always run LED's at 10mA regardless of the color. With less current, there is less draw on the battery whether it's running down or not. 20mA is close to the Absolute Maximum for a lot of LED's, and 10mA is reasonable. For many, many pedals, most of the battery power used goes for lighting LED's.
If you're using 1K, I'd suspect a wiring issue. Maybe something did not get wired as you intended because 1K should not cause that problem with an LED.

callaway · October 23rd, 2009, 05:31 PM

You can run them even lower. I use super-bright LEDs in my effects and I run them down to even 1 mA. Your luminous intensity will drop, but it's not going to make much of a difference in how bright it really is for this purpose. The lower current you run, the longer a battery will last!

dagger4 · October 23rd, 2009, 05:42 PM

Try for the clear blue ones 20k ohm on 9 volts.
Standard for normal leds is 4.7 k ohm on 9 volts.
Assuming that your wiring is direct from the 3 dpt switch

October 21st, 2009, 02:20 PM	#1 (permalink)
joinpobob Tele-Meister Join Date: Jun 2008 Location: Gainesville Age: 26 Posts: 166	LED Issues Hi, So I finished building a compressor pedal for a friend last night. It sounds great and seems to work well. I housed it and hit the switch; the LED shined bright blue for about 5 seconds, sputtered and then shut off. I just kept playing for a while and it came on intermittently. I then opened her up and measured the voltages. I had 9.33V coming off of the DC power jack, 2.1V at the Anode, and 0V (ground) at the Cathode. I have a 1K Ohm resistor between the DC jack and the LED, which I guess has 7.2V across it. Does that sound right? With everything still wired-up, I put a green led in parallel with the the blue LED (I just touched the leads together) and the green LED worked. I then put a blue LED in parallel with the original blue LED; in that configuration both turned-on worked for again about 5 seconds, sputtered and turned-off. I didn't have the energy to get the soldering gun out and just wanted to play some more. When I went to play again, it turned on, sputtered and went off. Any thoughts? Do blue LEDs need a bigger resistor (or a smaller one)? Thanks!

October 23rd, 2009, 05:42 PM	#5 (permalink)
dagger4 Tele-Meister Join Date: Aug 2005 Location: Groningen, The Netherlands Posts: 289	Try for the clear blue ones 20k ohm on 9 volts. Standard for normal leds is 4.7 k ohm on 9 volts. Assuming that your wiring is direct from the 3 dpt switch __________________ Chris Myspace Music: http://www.myspace.com/chrisschutter

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October 21st, 2009, 04:13 PM	#2 (permalink)
CA_Dan TDPRI Member Join Date: Oct 2008 Location: Los Angeles Age: 31 Posts: 53	From the StewMac website: To calculate the correct size resistor, subtract the LED voltage from the battery voltage, then divide by the LED’s current consumption (in amps) to give the necessary resistance. For example, a red LED normally runs at 20 milliamps at 2.2 volts. If you use a 9-volt battery you have (9V - 2.2V) / 0.02 amps = 340 ohms. 100 to 330 ohm resistor usually work fine. Depending upon your calculations, you may want to choose a resistor a little smaller to account for the battery running down.

October 23rd, 2009, 01:33 PM	#3 (permalink)
FenderLover TDPRI Member Join Date: Jun 2009 Location: Minnesota Posts: 65	I always run LED's at 10mA regardless of the color. With less current, there is less draw on the battery whether it's running down or not. 20mA is close to the Absolute Maximum for a lot of LED's, and 10mA is reasonable. For many, many pedals, most of the battery power used goes for lighting LED's. If you're using 1K, I'd suspect a wiring issue. Maybe something did not get wired as you intended because 1K should not cause that problem with an LED.

October 23rd, 2009, 05:31 PM	#4 (permalink)
callaway Tele-Meister Join Date: Jun 2009 Location: Blacksburg, VA Posts: 162	You can run them even lower. I use super-bright LEDs in my effects and I run them down to even 1 mA. Your luminous intensity will drop, but it's not going to make much of a difference in how bright it really is for this purpose. The lower current you run, the longer a battery will last!

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