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help with blue led


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Hi Got Lost,
Welcome to our forum. ;D
Your 555 LED flasher circuit doesn't have enough supply voltage for the voltage requirement of a blue LED plus the voltage loss at the high output of the 555.

A blue LED's voltage requirement could be 3.6V. The voltage loss at the output high of a 555 could be 2.25V, but is typically 1.4V.
3.6V + 1.4V= 5V so only 1V is across the 330 ohm current-limiting resistor resulting in only 3mA. If your 555 has a voltage loss of 2.25V then the LED's current is only 455uA.

The circuit's supply voltage was probably selected for it to use 1.8V red LEDs, wasn't it?

Have you checked that the LED and capacitor aren't installed backwards?


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