driving 7seg displays

Hi

I need some help with my project:

I am using TTL logic to drive common cathode dual displays. On some inputs to the display I have nearly 5v (approx 4.8v) but it's not enough to light the display. There is not a problem with the individual segments as they light when they're connected to the 5v rail via a resistor. I need a way to boost the output from the logic to 5v so it will light the display.

Any ideas welcome

please reply a.s.a.p as the deadline is soon!!!

cheers

What IC are you using? I suspect it is open collector and you are driving a grounded load with no pullup resistor.

the input is coming from a 74LS32 ( quad OR gates) I have grounded the common pins through 300 ohm resistors, but am not using resistors to each segment input.

hope this extra information helps

please reply on how I can solve this problem

The LS device can only source .4mA in the high state, it can sink 8 mA in the low state. You need to connect the display from VCC to the outputs and reverse the logic.

:evil: you say you have an already high output and u dont necessarily need 5 volts to drive an led, most leds turn on around 2 volts, you will have to put current limiting resistors between chip and display so you dont burn out the display, check ur biasing on ur display too and depending on what ttl driver/decoder ur using if ur still getting a screwy output i know with some projects i had to invert the bcd input so theres just some things to think about :twisted: