How to increase brightness on multiplexed 7 segments?

[Ma3ix]

Hi,

maybe it´s time to give an updated schematic...

Klaus

Here it is
Should I reduce PNP base transistors from 10k to for example 8.2k ?

 

[FvM]

I didn't notice yet that your processor is a 8051 but the circuit is probably not designed for 8051 ports. Driving the NPN transistors through 2K2 resistors doesn't work because all ports have only weak pull-ups instead of strong push-pull drivers. Or do you have additional logic gates not shown in your schematic.

This issue has to be clarified first, reducing series resistors might be checked later.

 

[Ma3ix]

I didn't notice yet that your processor is a 8051 but the circuit is probably not designed for 8051 ports. Driving the NPN transistors through 2K2 resistors doesn't work because all ports have only weak pull-ups instead of strong push-pull drivers. Or do you have additional logic gates not shown in your schematic.

This issue has to be clarified first, reducing series resistors might be checked later.

A/D connected (from P1.4 to P1.7 ) and LM 35

Im using AT89S51
"Port 1 is an 8-bit bi-directional I/O port with internal pull-ups. The Port 1 output buffers can
sink/source four TTL inputs."

It works on BreadBoard...

What do you suggest?

 

[FvM]

It works on BreadBoard...

"Working" yes, but only sourcing about 100 µA instead of intended 2 mA to BC337 base. Respectively limiting total digit current to 30 or 50 mA.

If I'm right that the low digit driver base current is the problem, you'll notice that brightness reduces when multiple segments in a digit are turned on.

Simple workaround is to connect port pins directly to BC337 base and use 2.2 k as pull-up between base and +5V.

 

[Ma3ix]

"Working" yes, but only sourcing about 100 µA instead of intended 2 mA to BC337 base. Respectively limiting total digit current to 30 or 50 mA.

If I'm right that the low digit driver base current is the problem, you'll notice that brightness reduces when multiple segments in a digit are turned on.

Simple workaround is to connect port pins directly to BC337 base and use 2.2 k as pull-up between base and +5V.

Many thanks ,you were absolutely right!:thumbsup:
Now I have problem how to reduce brightness:lol:

I should put back 330 Ohms on segments.. Are all others values in circuit good (10k for PNP base, 2.2k NPN base)?

 

[FvM]

You can still reduce brightness by increasing off-time delay in favor of on-time delay (= pwm dimming).

 

[haydon.wang]

hello, maybe you can reduce delay time 100ms to 50ms. and should be reduce flickering. for why use ISR to manager it , i think if use ISR, and then mcu can use more time to do with other task. this is my opinion.