led sign board

[mateen_oct]

Hi,
i am trying to make led sign board "REPAIR SPECIALIST" with the size of 18"H x 24"W, in 2 lines approximately with 400 5mm blue ultra bright led in series, with 12V dc power supply, can someone please help me to design the circuit,
thanks
mateen_oct

 

[crutschow]

If the forward voltage for the leds is about 3.5-4V, then you would put a maximum of two in series with a resistor. For a 20mA The resistor value would be (12 - 2*3.5)/20mA = 250 ohms. Just do that circuit for all 400 of the leds (200 circuits consisting of 2 leds and a resistor, all connected in parallel to the 12V dc supply).