74LS154, All the LEDs lights up when there is no input

[kinton cloud]

Hello everyone,

I just want to ask why all the LEDs lights up when there is no input in 74LS154 IC? The first LED should turn off when there is no input right? Can anyone tell me what did I do wrong?

Here is my circuit


Note: If anyone else is wondering where that oval shaped wire at the right, I used it to short the pin 18 and pin 19. It is not connected to anything.The output is still the same either I remove it or not.

 

[(*steve*)]

Because when either G1 or G2 are open, they will float high. Hafing either of these inputs high will cause all outputs to go high.

G1 and G2 (pins 18 and 19) need to be tied low, not just tied together.

edit: once you fix this, the LAST led will turn off (because all the other inputs will float high)

 

[kinton cloud]

Because when either G1 or G2 are open, they will float high. Hafing either of these inputs high will cause all outputs to go high.

G1 and G2 (pins 18 and 19) need to be tied low, not just tied together.

edit: once you fix this, the LAST led will turn off (because all the other inputs will float high)

I see, thank you very much. Re-reading the datasheet make more sense now, I didn't understand it at first.