Velleman К8088 - Manual (Page 10)

10
LED:
LEDs require a series resistor (R4, R5 or R6)
Determine led voltage drop (Check manufacturer datasheet).
Rule of thumb: red: 1.7V, green: 2V, blue: 3..4V).
Next, check required LED current.
Example:
Red LED, 1.7V drop, required current: 20mA
Resistor calculation: (12V-1.7V) / 0.020 = 515 ohm (choose nearest value,
e.g. 560 ohm)
Resistor power rating calculation: (12V-1.7V) x (12V-1.7V) / 560 = 0.19W
(choose a 0.25W resistor)
Connection
12VDC
- +
C (-)
A (+)