I want to detect logic of the mains supply (230VAC, 50Hz) and feed the output of HCPL-3700 into ATmega16L. I read through the datasheet but could not understand how to calculate the resistor values. Does anyone have an idea of how to go about doing this?
I am referring to application note on HPCL-3700, page 5 under AC Operation With No Filtering
Assuming 60% criterion, 230 x sqrt(2) x 60% is 195V. choosing closest whole value of 200V instead of 195V.
Rx = (V+ - VTH+) / ITH+ = (200V - 5.5V) / 2.5mA = 38.9 Kohms.
choosing round figure of 40 Kohms for Rx. I can use two 22 Kohm resistors.
Calculating power dissipation in 22 Kohm resistors
P = (I*I) * R
= (4.4mA * 4.4mA) * 22K (where 4.4mA is Iin)
= 426 mW
So, choosing 22 Kohm resistors with 500mW power rating.
How does this answer look? I think I'm wrong because there are few things that still don't make sense.