[Ubel]

Originally this topic was about the post below, but I'd like this answered and I don't want to create another topic for something which I believe is simple.

I have a larger sized Green LED, I don't know what size, you can see a photo of it ON here.

I used the 10Kohm resistor that Tangent says to use for smaller LEDs, and as you can see the LED is -very- dim. What size resistor should I use for a LED this size? Running on just 9v, not planning on anything higher.

Thank you,
Joseph




Basically I'm building a CMoy, it's built and working but I realized I bought a single channel 10k ohm pot on accident, went to Radioshack but they only had 100k dual channel pots.

I bought one of the 100k dual channel pots, but now I need to know what'll happen if I use it on a CMoy using Tangent's plans. I believe the volume will be lower?

Is there a way to change the resistance of the pot, is there an actual resistor in there or is it due to the windings that make up the resistance?

Thank you,
Joseph

 

[Zigis]

100K is OK. Volume remind the same. Increase R2 to 1Mohm.

Zigis.

 

[Ubel]

Okay I did what you said and changed out the R2 to 1Mohm, it works fine when I plug it in directly. But I can't get the pot to work, when I wire it up there's lots of static, like white noise but all over the place.

The pot's model number is ALPS 625G 100KAX2. I looked up how to hook it up and I did it correctly.. but it won't work.

Help someone? Thank you

Joseph

 

[Ubel]

I googled around and someone said that 4/5 ALPS pots they got from Radioshack had bad lining. Do you think this is a bad pot?

I tested it with my multimeter and the max I can get out of it is about 85k ohm, I donno if my multimeter is off or if the pot is off?

I'd guess for low volume I want max resistance, and for max volume I want no resistance?

Sorry about all the questions, I'm new to working with pots.

Joseph

 

[mr-awesome]

theres something on this site about 100k pots i remember looking at it myself when i started my cmoy, you have to change the resistors quite a bit, search for it, it might be on the headwize forum you should try looking there too.

or you could buy 2 single channel pots and have one for the right ear, one for the left, if you get desperate.

 

[Ubel]

Yeah I was thinking about two singles, didn't wanna do that though.
I know I'd have to change resistors.. hoping what Zigis said is right.. donno.

Anyway I found a 100Kohm and a 10Kohm dual channel pot out in the garage.. -.-

Donno if I should try the 100Kohm I found or switch the resistors back to 100k and then use the 10Kohm I found..

Joseph

 

[Ubel]

Okay I got it, turns out I was testing it and while testing I absentmindly was testing just one channel, which was the problem. Hooked them both up and it worked.

Got it all in its Altoids tin now, sounds great. I love it.

Thanks to you all

Joseph

 

[Ubel]

Anyone who'd know, please read the original post as I need help with this LED.
Thank you. I'm sorry for asking simple questions like this but I'm new to smaller electronics.

Sorry,
Joseph

 

[Zigis]

Size no matter. Talking about LED.

Try 10k first, if too dark, try smaller R. Smaller R - more bright, larger R - longer battery live.

Zigis.

 

[Ubel]

Yeah, I figured.
I'm using a 10k now, should I try 5k? Would that be twice as bright?

It looks pretty bright in that photo, but actually you can barely tell it's on, even in a dark room.

Joseph

 

[Zigis]

Try 5K.
It take more current, but if You can't see it's on and forget switch off, it take much more current. I now this, my first CMoy was without LED, always forget switch off.

Zigis.

 

[NeilR]

The best way to tune the LED is to just try different resistors with it until you are happy. You can do this with a spare LED, resistor(s) and a battery. Try 5KR and 7KR for starters. RadioShack sells a pack of jumpers terminated with mini alligator clips; that is a handy thing to keep around for tests like this.

An even better/easier way is to get a 10K or so pot or trim pot. Set it up (before hooking up the battery!) so that the pot is adjusted for max resistance, then hook up the battery and slowly reduce the resistance of the pot until you like the brightness. Disconnect the battery, read the resistance, and install a resistor close to that value. I do this on a breadboard before I install the LED in my project.

 

[Ubel]

Thank you both.
I figured I could do that with a 10KR pot NeilR, but I didn't try it.
I have some jumpers like that, very helpful.

Thanks for the suggestions. Specially Zigis as without him telling me to replace R2 my CMoy wouldn't be running.

Joseph

 

[mono]

The problem with an unknown LED is you lack specs for it's Forward Drop.

Suppose you had a forward drop of 2V, and were connecting the LED and series resistor to the power positive and negative, not to amp virtual ground.

You'd have 9V (actually you need the real voltage of your battery if a NiMH, might be 7.2V or even 9.6V for example) so 9V -2 = 7V. Determine what current you want through the LED. "Typically" with a modern high efficiency LED, 5mA is plenty bright enough as an indicator but if you want an especially bright lighting effect or have an old less efficient LED, maybe you're looking for 10-20mA, let's say 10mA or 0.01A.

Anyway, taking above 7V/0.01 = 700. In the above proposed scenario you would pick the closest resistor you have handy or can find near 700. A common value might be 680 Ohm.

This is a lot lower than some people use, but they may have a different LED or voltages to work with, so the math bears out why. If you have a lower voltage (9V) instead of a higher some use (24V is popular or two x ~ 9V cells in series), and the LED needs or you want more current, the resistor value drops a lot.

Personally I would think about getting a different LED for an amp running off a 9V battery as ~ 10+mA is a significant percentage of current and will reduce runtime of the amp. Maybe you don't need 10mA or your forward voltage drop isn't actually 2V, the larger values others suggest are a good place to start when unsure. Better to shoot towards conservatism and find the LED still isn't bright enough rather than putting too much current through it, decreasing it's life too much or burning it out.

 

[Ubel]

Okay great, I replaced it with a 1Kohm, sounds low but that's where it got to the " bright enough " point. It's no where near as bright as it could be, but good enough.

Thanks for the idea about the Pot NeilR, that's what I did and it worked great.

Joseph