Led brightness

[Smartweb]

I connected 8 leds in series and pulsed it via a microcontroller pin while sinking the current using 74hc154 decoder.The led is not bright enough to be seen. Can someone help me with solution. Please

 

[MikeMl]

What voltage are you starting from? You might have to reconfigure into a four in series and two strings in parallel arrangement. Dont forget you need a current-limiting resistor in each string.

 

[Smartweb]

Thank you Mike ML. I am using 5v to power the microcontroller and the 74hc154.

 

[ericgibbs]

Thank you Mike ML. I am using 5v to power the microcontroller and the 74hc154.

hi,
Whats the value of the current limiting resistor to the LED and what is the colour of the LED.?
Pulse width and pulse rate.?

 

[MikeMl]

Are you trying to light all eight LEDs with a single pin on the 'HC154? When operated off 5V, the 'HC154 is only rated to sink ~5mA. The only way you could use it to light 8 LEDs is by being very tricky, and by using another power supply.

Post a diagram showing what you are trying to do.

 

[Hero999]

You'll need at least 1.8V*8 = 14.4V to drive eight red/orange LEDs in series, in reality more because there needs to be enough headroom for a current limiting resistor.

If they're blue/violet/white you'll need 3.5V*8 = 28V.

You need to drive the LEDs using a transistor.