Datasheet

Supply voltage (V) - led voltage (V)
required current (A)
= series resistance (ohms)
required current (A)
= series resistance (ohms)
Required resistor power handling= voltage over resistor x current passed trough resistor
9V - 1.7V
0.005A
= 1460 ohm
9V - (3 x1.7V)
0.005A
= 780 ohm
(9V - 1.7V) x 0.005A = 0.036W
closest value :
use a 1k5 resistor
use an
820 ohm resistor
a standard 1/4W resistor
will do the job
Supply voltage (V) - (number of leds x led voltage (V))
How to Calculate the series resistor: Example: operate a red led (1.7V) on a 9Vdc source. Required led current for full brightness: 5mA (this can be found in the datasheet of the led) LEDs in series: Example: 3 x red led (1.7V) on 9V battery Required led current for full brightness: 5mA (this can be found in the datasheet of the led)
Leds feature a speci¿ c voltage drop, depending on type and colour. Check the datasheet for exact voltage drop and rated current !
Never connect leds in parallel
Leds and how to use them
An open collector output can be compared to a switch which switches to ground when operated
Example: How to switch an LED by means of an open collector output
open collector outputs