Hi folks,

I have a question about how to drive a Kingbright 12 segment bar graph display:

http://www.farnell.com/datasheets/1776593.pdf

Here's the schematic:



I have no problem driving a 10-segment display using an LM3914. The problem I have is that, for example, LEDs B and C are connected in series. Some specific questions:

- I know the LM3914 controls the current... if I drive the two series LEDs B and C as a single LED using an LM3914, will they be driven by the same current as an individual LED (say A)?

- If I wanted to drive LEDs B and C separately, can this be done using an LM3914 and if so, how?

Thanks in advance!

 

B and C are not in series.

 

B and C are not in series.

If you don't connect pin 4 they are... I was assuming this is the only way I could do it using a 3914... my question is, would this work - or - how would you do it using pin 4?

 

- I know the LM3914 controls the current... if I drive the two series LEDs B and C as a single LED using an LM3914, will they be driven by the same current as an individual LED (say A)?

The problem here is that yes, same current will pass through B and C, but! You need voltage to turn led On. In A branch you only have 1 led. In BC branch you have 2 led, so you need twice as much voltage. So lets say you need 3 volts to turn A On. When you apply same 3 volts to BC branch, you will get no light. Why? Because you use 3 volts to turn 1 led On. To turn 2 led On you need twice the voltage, 6 volts and you don't have 6 volts, you only applying 3 volts to the BC branch. Since the BC branch led are not On, the current going through them does not matter.

 

The problem here is that yes, same current will pass through B and C, but! You need voltage to turn led On. In A branch you only have 1 led. In BC branch you have 2 led, so you need twice as much voltage. So lets say you need 3 volts to turn A On. When you apply same 3 volts to BC branch, you will get no light. Why? Because you use 3 volts to turn 1 led On. To turn 2 led On you need twice the voltage, 6 volts and you don't have 6 volts, you only applying 3 volts to the BC branch. Since the BC branch led are not On, the current going through them does not matter.

So how are you supposed to drive this display?

The LM3914 is a common anode device - so all the anodes are connected to Vcc. I'm assuming the LM3914 pulls the cathode to ground to turn it on. Assuming your Vcc is greater than twice the forward voltage of the LEDs then it should work... no?

 

Funny thing... I can not find Product Number DD-12CGKWB on their website... So I can not even look up application notes that they mentioned in the datasheet.

 

Looks like they don't make 12 segment anymore. I would email them and ask for the application notes that they mentioned in 12 segment datasheet.

 

Looks like they don't make 12 segment anymore. I would email them and ask for the application notes that they mentioned in 12 segment datasheet.

Here's a link to the product:
http://export.farnell.com/kingbrigh...ed-green-11000mcd-75mw/dp/2373481?Ntt=12CGKWB

They only have 18 of this one left so it must be discontinued (other colours are out of stock already).

Probably not a runner for my project in any case, but I'm still curious as to how you're supposed to use the thing!

 

Here's a link to the product:
http://export.farnell.com/kingbrigh...ed-green-11000mcd-75mw/dp/2373481?Ntt=12CGKWB

They only have 18 of this one left so it must be discontinued (other colours are out of stock already).

Probably not a runner for my project in any case, but I'm still curious as to how you're supposed to use the thing!

I am guessing it is for some type of microprocessor control, adding a few diodes and "charlieplexing" to operate it on a minimum number of I/O pins ( I am guessing 6).

 

If I wanted to drive LEDs B and C separately, can this be done using an LM3914 and if so, how?

Like this perhaps?

 

Here, looks like two sets of 3 pins on a Microcontroller. Each set of three pins can control 6 LEDs.

Charlieplexing requires that some pins are set as high impedance inputs to steer current flow. Therefore a Microcontroller is required.

 

With the LM3914 the LED current is determined by the IC. The value of the resistor between pins 7 & 8 determines the LED current. Going one step further the recommended minimum Vcc is 3V. I have used the LM3914 in many circuits with a VCC of 9 or more volts and only one LED each pin, and have also used the IC with LED's in series on the individual pins. I also have a good stock of 10 digit bar graph displays, I would be happy to send you send me a private message with your requirements.

Hi folks,

I have a question about how to drive a Kingbright 12 segment bar graph display:

http://www.farnell.com/datasheets/1776593.pdf

Here's the schematic:

View attachment 76386

I have no problem driving a 10-segment display using an LM3914. The problem I have is that, for example, LEDs B and C are connected in series. Some specific questions:

- I know the LM3914 controls the current... if I drive the two series LEDs B and C as a single LED using an LM3914, will they be driven by the same current as an individual LED (say A)?

- If I wanted to drive LEDs B and C separately, can this be done using an LM3914 and if so, how?

Thanks in advance!