How does a Bi-color LED bar graph work?

[radiant777]

Hello,
I'm rather new to this area but i'm trying to learn as much as I can. I just got a Bi-color LED bar graph (red/green) and I'm having trouble activating the green LED. I just used a single D size battery with wires attached to each end for power. This is just to see if I can activate the LEDs. Do I need more power? Here are the specs: **broken link removed**

radiant777

 

[bacterozoid]

Bi-color LEDs are nothing more than two LEDs. You can see in the schematic that there are actually 20 LEDs in your schematic.

What you probably want to do is connect pins 21-30 through a resistor (each one gets its own resistor) to ground. That resistor will provide current limiting and prevent you from burning out your LEDs. To get the value, use:

R = V/I, where V is your input voltage and I is desired current (20mA is a good value)

If you want to activate a green LED, apply VCC to any pin 1-10. If you want red, apply VCC to any pin 11-20.

 

[radiant777]

Thanks for the quick response, bacterozoid. Do have any suggetions as to what resistors I can use to hook up to the LEDs (red and green) to accept a 9v battery to supply power to both?

radiant777

 

[bacterozoid]

If you want 20mA, which is pretty standard for an LED, you will need 470 Ohm resistors.

R = 9V/20mA = 450. The 470 is the next standard value up.

 

[audioguru]

If you want 20mA, which is pretty standard for an LED, you will need 470 Ohm resistors.

R = 9V/20mA = 450. The 470 is the next standard value up.

No.
The LEDs use about 2V so the resistor has only 7V across it, not 9V.
7V/20mA= 350 ohms. 330 ohms will provide a current of 21mA which is fine.

A little 9V alkaline battery will not last long if it lights 10 LEDs at the same time and each one draws 20mA. The battery voltage will drop to 7V in about 30 minutes then the current in each LED will be 15mA which is not as bright as with a new battery.

 

[radiant777]

Thanks for the responses. I plan on hooking up the LED bar graph to a chaser circuit. So not all of the LEDs will be on at the same time. The circuit will allow 10 LEDs to be hooked up to it. Any suggestions to adding resistors would be helpful.

radiant777

 

[bacterozoid]

Good points, audioguru - thanks for correcting my mistake.

What question do you have about adding resistors to your circuit?

 

[audioguru]

My Ultra-bright Chaser projects use a 74HC4017 sequencer IC to drive the LEDs. Only one LED is lighted at a time so 10 LEDs use only one common current-limiting resistor.
My Chaser projects use pulse-shortening circuits so that the battery lasts a long time.

 

[radiant777]

What I would like to do is to have the 10 LED Bi-color bar graph (red/green)that I have to work with this simple 10 LED chaser circuit: https://www.elecfree.com/electronic/wp-content/uploads/2008/07/led-chaser-by-ic-4017-ic-555.jpg

Is this possbile?

radiant777

 

[audioguru]

The simple circuit should work fine.
The low output current from the CD4017 with a 9V supply will limit the current in the LEDs to 7mA to 15mA. The current will drop as the battery voltage drops as it runs down.

 

[radiant777]

Thanks for quick reply, audioguru.
Just for got to add what effect I'm looking for. What I trying to do is to start in the center of the bar graph. The LEDS would light up working there way out from the center and then work their way back to the center. One side would be red and the other side green. I'm sure this is very easy for you and others but complicated for me. Understand the basics but just need some help getting it to work properly.


radiant777

 

[audioguru]

You can start an LED bar-graph display with the center LED and work the way out from the center WITH ONLY ONE COLOUR. You can have one display red and the other display green if you use two bar-graph displays.

 

[radiant777]

Enteresting! Will have to look into your proposal. Wouldn't by any chance know where I could find bar graphs with just 5 LEDS in them?

Thanks for yur help,
radiant777