7 Segment Brightness Control Circuit

StudentSA

Member

• Aug 25, 2010

• #1

My project is nearing completion, just need to make minor tweaks (which are taking forever )

I`m using a MMC74C925 which is a counter with built in 7 Seg Mutiplexer/driver. I need to design some sort of a circuit using a single photo resistor to adjust the brightness of the LED`s.

Is there a standard method of doing this?

Regards,
StudentSA

 

C

colin55

Well-Known Member

• Aug 25, 2010

• #2

The simplest is to put a common-emitter transistor on pin 9 and adjust the brightness with a 100k pot between base and 5v rail. Then put your LDR across the pot.

 

StudentSA

Member

• Aug 28, 2010

• #3

I do not see how this will work??? Pin 9 is the "switch" for one of the 7 segment displays.

 

C

colin55

Well-Known Member

• Aug 28, 2010

• #4

Use pin 8 for 74C925

 

StudentSA

Member

• Aug 28, 2010

• #5

Seems plausible...

So basically control the amount of current flowing to ground.

Thanks for the idea, will try this as soon as I can.

Regards,
StudentSA

 

StudentSA

Member

• Aug 29, 2010

• #6

No luck with the common emitter and the ground pin.

However, I got it to work with the V+ pin. I took the collector to Vcc and the emitter to the V+ pin and the base to Vcc via Resistor and parallel LDR. Works like a charm.

Thanks Colin55