Pages: [1]   Go Down
Author Topic: What kind of Potentiometer do I need?  (Read 1104 times)
0 Members and 1 Guest are viewing this topic.
Offline Offline
Newbie
*
Karma: 0
Posts: 31
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I would like to control a bar of RGB LEDs I am going to make that will run off 12V. I understand I will need 3 to control the red green and blue separately. What kind of potentiometer will I need to do this?

Thanks
Macke
Logged

SE USA
Offline Offline
Faraday Member
**
Karma: 41
Posts: 3783
@ssh0le
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

with nothing else in the mix a huge expensive rheostat to handle the current

Logged


Offline Offline
Newbie
*
Karma: 0
Posts: 31
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I really need that big of one for 12V?
It will probably only be no more than 2A
Logged

Offline Offline
Newbie
*
Karma: 0
Posts: 31
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

12V DC if that is unclear
Logged

Left Coast, CA (USA)
Offline Offline
Brattain Member
*****
Karma: 361
Posts: 17293
Measurement changes behavior
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Probably have to know more about your 'bar of rgb led's and how they are wired up. A drawing showing the individual leds and how they are wired to each other would be a good starting point. And on using a pot to adjust current flow, I would propose that you are best off using both a resistor and a pot in series such that turning the pot to 'zero ohms' position doesn't burn everything up. Calculate the fixed resistor to set the absolute maximum current flow and then allow the pot to dim from there.

Lefty
Logged

Offline Offline
Newbie
*
Karma: 0
Posts: 31
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

The RGB bars will be wired up in parrellel with each LED getting 3 resistors. So I don't think I would need the resistor in front of the pot, because there is resistors on the LEDs.. There will be 4 wires going into the Bar, with one red, one green, one blue, and a ground. With a pot on each of the RGB wires. If this does any good please respond or ask more questions of what you need to know, all I need is 3 potentiometers that can resist the flow of 12V DC.

Thanks
Macke
Logged

The Netherlands
Offline Offline
Edison Member
*
Karma: 49
Posts: 1631
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

You don't understand the reason for the questions (which is also the reason why the first respondant showed you that monster).
12 volt doesn't tell us anything.
You probably do not want to control the voltage, you want to control amperage.
To be sure about that, we need to know how your bars are built.
How many LED's are in there and how are they hooked up.
Are all LED's of the same color in parallel (all A's together and al K's togehter), or are they series connected (K of LED 1 connected to A of led2, K of 2 to A of 3 and zo on), or any combination of these two possibilities ?
What resistors are connected to the LED's ?

Controlling the brightness of LED's should not be done by a potentiometer, if that is your goal.
There's a much better way to do this, certainly if you're using an Arduino.
Logged

Have a look at "blink without delay".
Did you connect the grounds ?
Je kunt hier ook in het Nederlands terecht: http://arduino.cc/forum/index.php/board,77.0.html

Offline Offline
Newbie
*
Karma: 0
Posts: 31
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I don't know my specifics yet, but like I said the LEDs will be in parrellel with the reds all connected, the greens all connected, and the blues all connected, and ground all connected. The purpose of this is to not use an arduino so I can save 30$. If I was using arduino, I would know exactly how to do that. But is there any way just to give me a general pot I could probable use? Also, my power supply will probably be 2A so I know my LEDs wont draw more than that.

My RGB LEDs will use 20mA so say I have 12 RGB LEDs, that's technically 36 different LEDs, so 36 times .02 = .72, so my bars will probably be right about .72 AMPS.

If that helps clear things up and I can get an answer, great, if not, ask more questions. Also I don't need an EXACT potentiometer, just like a general idea of what I would need. I'm mainly in planning staged right now and am looking at the cost. And then I might order them.

And also, why shouldn't the pot control LEDs? I understand the duino can do this much easier, but once agin, cost. I don't understand why pots shouldn't do this job, seeing is they are pretty much variable resistors, which is what I want to do, vary the resistance to control brightness..


Thanks
Macke
Logged

Offline Offline
Newbie
*
Karma: 0
Posts: 31
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

It looks likei might be able to use a 1K pot as in this tutorial. He is using 9V DC and I don't know how many amps but this might work, would it?

Here's the link..
http://www.instructables.com/id/Simple-RGB-LED-MOOD-Colour-Potentiometer-Without-M/

Logged

SE USA
Offline Offline
Faraday Member
**
Karma: 41
Posts: 3783
@ssh0le
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

depends on current, that joker I posted above is only rated for 1.4 amps no matter the voltage, and its going to get hot pretty quickly. I use them frequently at work using 9 to 16 volts

this is why we like PWM, a small pot a 555 (or arduino) and a fet can achieve the same thing without burning off current as heat
« Last Edit: December 24, 2012, 04:20:42 pm by Osgeld » Logged


The Netherlands
Offline Offline
Edison Member
*
Karma: 49
Posts: 1631
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Quote from: tmacke17
why shouldn't the pot control LEDs?

Because you will probably be regulating voltage instead of amperage.
LED's brightness can be set a lot smoother, safer and have a much better range by using PWM and thus using an Arduino, but ofcourse you can also use a 555.
Using a 555 and a few components will save you some money, but you'll have to build a PCB or use a breadboard (times 3).
To save space you could also consider a 558 which is 4 * 555 in one.
Logged

Have a look at "blink without delay".
Did you connect the grounds ?
Je kunt hier ook in het Nederlands terecht: http://arduino.cc/forum/index.php/board,77.0.html

Offline Offline
Newbie
*
Karma: 0
Posts: 31
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Well then if its going to be that much trouble I guess it's going to be with an arduino... Any one know of any cheap arduino clones?

I know of the teensys but those are just about as much as a arduino from amazon.. So...

Thanks everyone, I guess I misunderstood potentiometers!!
Macke
Logged

The Netherlands
Offline Offline
Edison Member
*
Karma: 49
Posts: 1631
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

If you're going for cheap, you can consider a chinese nano board.
They are cheap, small and offer enough for your LED bars.
Shipping is often included in the ridiculous low prices but you might have to wait for 2 - 4 weeks for them to arrive.

As there is no financial contribution to the Arduino community in these low prices, you might consider donating a bit some time in the future as a thank you to it.
Logged

Have a look at "blink without delay".
Did you connect the grounds ?
Je kunt hier ook in het Nederlands terecht: http://arduino.cc/forum/index.php/board,77.0.html

0
Offline Offline
Shannon Member
****
Karma: 206
Posts: 12092
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Surely a 555 timer and a MOSFET switch can do PWM cheaper than an Arduino?  Something like:
Logged

[ I won't respond to messages, use the forum please ]

Pages: [1]   Go Up
Jump to: