connect 74LS47 to seven-segment display does not work?

[Shank747]

From the datasheet, the forward voltage, v(f) has a maximum value of 2.00 V and the i(f) is 20 mA. The resistance is then exactly 100 ohms, just as you predicted!

[Tom__Sedlack]

There's a little bit more to the calculation then what it appears you are doing.  Remember, you need to take VCC into account as well.  Say you are using 5V for VCC and your spec sheet shows a voltage drop of 2V across the LED.  Your current limiting resistors needs to drop 3V across it (VCC - v(f)).  If you want 20mA through the resistor and LED, using Ohm's law, the resistor will be 3V / 0.020A = 150 Ohms.  

[Shank747]

I will definitely keep this precious info in mind. But for now, i have already built the actual circuit (using all the previous components, including IC 7448 and 7 x 100 ohms to the LED, etc). I have the final circuit on Veroboard right now infront of me and i don't know why but segment g in the LED refuses to light up. I've tested the LED separately and all the segments work fine, but when soldered into the circuit, everything works fine (the levels change as expected) except for segment g which simply refuses to light up. Maybe you could help to diagnose the error? How to know which connection to which IC might not be working without having to dismantle and rebuild the entire circuit? I would rather not have to redo all this hard work all over again. I've indeed grounded all the pins as discussed earlier. The levels move from 0 to 7, except for segment g in the LED which just doesn't light up.

[Shank747]

I figured it out! I tested the LED's pin 10 (which handles segment g) via the series resistor and it turns out that the soldering joint appears OK on the outside, but inside it's probably filled with air as the conduction is really poor. So i reworked that connection betweent the resistor and the Veroboard again and voila!

[axid]

when i use seven segment display it t does nowork why?

[Tom__Sedlack]

Should be a common anode display

[axid]

when i used anode display it show different results

[Tom__Sedlack]

Slow your clock down and watch the sequence of the indicators. If you are counting up from 0 to 9, take note of the abcd values as displayed vs. what they are supposed to be.