Thread: 7 segment display help!! (SOLVED)

Hello all,

I'v started a simple project to display alphanumeric characters on the 7 segment LED display by connecting it to the MCU. The problem I'm facing is the characters are very dull. Number '1' is bright but number '8' is very dull. I'm using two displays to display from 0-99. Thanks in advance.

You must be using a resistor as a current limiter. What you need is a constant current source to drive the segments.

Actually, I think the problem is that all the segments are powered through the same current limiting resistor. As more segments are switched on, more current flows through the resistor and therefore there is a larger voltage drop across the resistor. This is why, when displaying an 8, the brightness is very low.

To solve the problem, place a resistor not on the common line, but on each of the 7 lines (8 if your display also has the '.' character) driving each segment.

The better type of 7 segment display, in my opinion at least, is the type with a common ground connection. For these you can easily use a transistor (normal NPN type) to switch on each segment. This ensures that the microcontroller doesn't take too much load, and all your segments are nice and bright - always.

better post your circuit diagram

try using amplifier IC like ULN2003
to amplify the current and to maintain that current when all the LED are turn ON

Originally Posted by Deepak350

Hello all,

I'v started a simple project to display alphanumeric characters on the 7 segment LED display by connecting it to the MCU. The problem I'm facing is the characters are very dull. Number '1' is bright but number '8' is very dull. I'm using two displays to display from 0-99. Thanks in advance.

You must use seven segment driver like 74LS47 (TTL) or 4511 (CMOS), so the led light will be stable.

Hello everyone and thanks a lot for the replies and my sincere apologies for the late replies. Well my problem is solved.

Originally Posted by zx_sa

Actually, I think the problem is that all the segments are powered through the same current limiting resistor. As more segments are switched on, more current flows through the resistor and therefore there is a larger voltage drop across the resistor. This is why, when displaying an 8, the brightness is very low.

To solve the problem, place a resistor not on the common line, but on each of the 7 lines (8 if your display also has the '.' character) driving each segment.

The better type of 7 segment display, in my opinion at least, is the type with a common ground connection. For these you can easily use a transistor (normal NPN type) to switch on each segment. This ensures that the microcontroller doesn't take too much load, and all your segments are nice and bright - always.

I did just that (individual resistors instead of one common) and the problem is solved. Again thanks a lot to everyone for the replies.

Regards,
Deepak350

can you post the diagram

Hi,

This is the circuit diagram similar to my board.

This is idealy wrong. Emitter of the Pnp transistor should be connected to +ve supply & collector should go to common of 7-segment CA display

In the diagram the transistor used is PNP, our transistor is a NPN. Sorry for the mistake.