Choose resistors for optocoupler (optocoupler)?

Question

Arduino

Hello, help me choose resistors for the optocoupler
OPTRON = LED2 + T1
+ there is a Schmidt trigger (IC2A) to get the log level, of course, it is probably not necessary, but it is still used in the circuit to prevent button bounce .. . and since there were free triggers, I used
this piece of the circuit PROXIMITY SENSOR
KTIR0821DS - optocoupler .. the datasheet is
heated by a resistor that is on the LED (150 ohm, not correct in the picture)
and on the 1kΩ phototransistor
and another question is the optocoupler is needed only in a short period of time
can it hang it on a field worker and turn it off when not needed?
to extend life?

Answer 1

According to the datasheet, the nominal voltage drop on the optocoupler LED is 1.2V, with a permissible current of up to 50mA. The typical value of the current through the LED is 20mA.
Total: with a nominal voltage drop across the diode of 1.2V, a current of 20mA and a voltage of 5V, we output a damping resistance of 190 Ohms. This value is absent in the series of resistances, the nearest figure is -200 Ohm. At the same time, the power of the entire vepi is 100 mW, so the resistor must be taken with a power of at least 0.125 W.
To calculate the resistance of the resistor in the load of the phototransistor, you need to understand which consumer you have hanging in the circuit further. What is the resistance of the consumer. If you have a CMOS logic with > 1mΩ at the input, then a resistance of 1kΩ is enough, but you can put 10kΩ, why suck the extra current from the power source?
Regarding the power off: what prevents you from directly lighting the optocoupler LED from the foot of the microcontroller? Almost any controller will pull 20mA without additional funds. There is no point in raising the current higher.
Plus, according to the same datasheet, the current limit for an LED is 50mA, if you lower it to 20 or even 10mA, then there is no point in worrying about the service life, the diode will last longer than you need.