thinking about making brake lights and signal lights with LED's for my bike and making them flash in different ways.
would it be recommended to use a resistor for each LED or will one resistor with say 5 LED's in series and a NPN work ok?
series led's need just one resistor, parallel led's need one resistor for for led.
series you will need more voltage since 5 (I'm guessing red) led's will need about 12v.
parallel you just need 2.4v and can easily power it even with two ni-mh aa cells.
btw, what current is each led rated for? if it's very low then you won't even need and NPN
Are you talking about a pushbike or Motorbike?
Commercial LED lights and indicators for cars and bikes use PWM to run them
and making them flash in different ways.
If the LEDs have to be individually addressed/controlled you need a resistor for each LED.
If they are all going to flash on & off together, then you can put them in series with one resistor and drive them with a higher voltage & a transistor or MOSFET. (That is, on resistor and one transistor for the left, and another setup for the right, and another if brake lights are separate.)
And, you can use PWM to dim them for tail-light mode.
Have you done any experimenting to check the brightness? A bicycle isn't too critical but if it's a motorcycle run the LEDs side-by side with the existing lights (or car lights if the existing ones don't work) and make sure the LEDs are at least as bright as the originals.
Commercial LED lights and indicators for cars and bikes use PWM to run them
I assume you're talking about high-power LEDs and constant-current switching drivers? That's not just PWM... That's PWM inside a constant-current feedback-loop. The PWM doesn't go to the LEDs.
ok, thanks.
I was planning on using the transistor to cut down on the number of digitalWrite pins compared to the number of LED's
since it would be a series/parallel LED circuit and I would most likely be using 12v LED's
probably about 20 or so. the project is still in idea phase
why not use a neopixel strip.