led resistor value quick question.

[pazuzu]

i have 5mm red led, and 470k, is this correct. i used an online calculator and 470 sounded familiar. i have been out of the hobby for about a year.

[twabelljr]

470k is really high. 470 will work. I use the typical forward supply voltage and typical forward supply current of the LED specs. and use this calculator: http://www.muzique.com/schem/led.htm

[pazuzu]

yea i used that calculator calculator. i do not understand the "led current". where do i find this value? is this the ma value coming from my power supply, ie the adapter? this is a valvecaster so there is no battery harness.

[twabelljr]

It is on the back of the package if you still have it. A Radio Shack 5mm blue is 20mA, 3.7V which equals a 265ohm resistor.  Without the spec. available 470 is a good value. Alot of off-board wiring diagrams use a value of 1K. The lower the resistor, the brighter the LED, but too low and POW!!!

[pazuzu]

ahh, ok. i got these from futurelec so they were just in small bags. the calculator specifies 353 in this case, but the with a higher value than i'm safe. thanks. i was hoping there was a problem because the pedal is acting "goofy" since i added the led to the switch.

[twabelljr]

the pedal is acting "goofy" since i added the led to the switch

Sorry to hear that. If it worked fine before just retrace everything you did and hopefully you will find a simple solution.

[pazuzu]

yea, it's odd. it will completely lose power, for a few seconds, and the led will cut out too. probably the ac jack. that in itself wouldn't worry me, but i will get surges where the circuit will get incredibly noisy and i will quickly unplug it. i can then plug it right back in and it will be fine. thing is i followed the dano "build it off the tube socket" method, so trouble shooting is out of the question. if i can't get it going it will and up being a rebuild with a circuit board. not sooo big of a deal i guess. it's already boxed up so i would just have to desolder everything off the tube socket and then put wire on it to run to a new board.

[soupbone]

i have 5mm red led, and 470k, is this correct. i used an online calculator and 470 sounded familiar. i have been out of the hobby for about a year.

Usually a 2k will work fine.

[pazuzu]

yea so the higher the value the less chance of frying the diode correct? than i will go with a 2k and see if that solves the problem. maybe the led is drawing too much current tubes are finicky things after all.

[DiscoVlad]

The LEDs I tend to use are like looking into the sun unless you use anything less than 4.7k... Just because it's rated at 20mA doesn't mean it has to be run at 20mA, usually 5-10mA is fine.

[twabelljr]

I never thought about substituting a mA rating I would like the LED to run at in the caculator. I usually use it to get the minimum value that will allow the LED to operate safely. If it is too bright I will raise the value from there to suit my "eye taste". The blues and whites can be VERY bright, even when testing with a meter! Wear your shades

[pazuzu]

ok i have isolated my problem to the led. what is happening is after about 10 minutes of running my valvecaster the hiss begins to escalate and become increasingly noisy. i let it build up and right as it began to get really loud i went in and desoldered the resistor from the power jack, and voila, it went away. i am assuming the led is heating up to the point of burning out?

has anyone else ever experienced this? i am thinking the first thing to do is to (increase?) the resistor value. correct? the higher the value the dimmer the light correct? remember i purchased these leds from futurlec so there is no ma value on the bags they came in.

[Barcode80]

You've got a wiring issue somewhere. Your LED, shouldn't be touching any part of the circuit except where the current limiting resistor of your LED connects to the common 9v supply. Can you post some pics of your wiring?

[pazuzu]

i could. but i am embarrassed. it's a spaghetti fest. i think it was the resistor itself. i swapped it out for another 470k and it has been running now without incident, i'll post here if i the issue persists. i still have some bugs to work out, some grounding issues. a little buzz when i touch it. i didn't use shielded wire and the box isn't shielded itself.

all in all i am quite pleased with it for a first shot at the valve caster with no debugging needed except for the led, which was a soldering mistake. i'm pretty sure the resistor got fried from heat. (point to point).