Why a 500 Ohm resistor

[netdata-be]

Hi there,

I'm developing my own PCB because and I'm using your project as a base, thanks for that !

I'm just wondering why you picked a 500 ohm resistor, let me try to explain:

• 5V / 510 Ohm = 0,0098 A == 9,8 mA
• 3,3V / 510 Ohm = 0,00064 == 6,4 mA

Since an optocoupler is just a LED it is designed to have 20mA over the IR LED

This means the ideal resistor should be:

• 5V / 0,02 A = 250 Ohm
• 3,3 V / 0,02 A = 165 Ohm

I'm guessing the led emits enough IR to activate the collector and thus work. Or I'm I missing something?

[philibertc]

Hello,

You are right, 250 Ohms resistors would be enough for that, but using about 500 allows to have a margin, because of the variable quality on sites like AliExpress but also to draw as little as possible on the 5V supplied by the stove.

Best Regards, Philibert

PS: I'm closing this issue but you can still comment https://github.com/philibertc/micronova_controller/issues/34#issuecomment-1053326781