Optocoupler to microcontroller input

[villager]

I'm doing some simulations with optocoupler as a switching circuit to isolate between between high voltage input and a PIC16F690 mcu. Using Proteus simulator, I made the following circuit:



The forward current and typical voltage for the LED of the 4N25 are 50 mA at 1.3 V typically as rated in the datasheet. The 215 ohm anode resistor was calculated based on an assumption that the input is a 12V swinging signal (high and low), which I mimic by using a button, so it was chosen to provide the 50mA current at 1.3V drop for the LED. The 10Kohm pull-down resistor is used so that whenever the input signal is high, the collector will conduct current via the 5V supply down through the emitter.

I wrote code that tells whenever the signal at RB4 is high, RC0 goes high and the blue LED illuminates. Whenevr RB4 goes low, RC0 goes low and the blue LED turns off. The code is written using Mikroc IDE.

Code: [Select]

void main() {

ANSEL = 0x00;
TRISC = 0x00;
TRISB=0xFF;
PORTC = 0x00;
OSCCON = 0b01110001; /* set internal clock to 8 MHZ */
OSCTUNE = 0x1F;

for(;;){

if(PORTB.B4==1){

PORTC.B0=1;

}else

PORTC.B0=0;
}
}
The problem is that when I run the simulation, the blue LED doesn't illuminate regardless of the button state (pressed or not). But when I reverse the condition statement to if(PORTB.B4==0), it illuminates. It's been so long since I typed a code, so it could be a problem in code, configuration or hardware. What do you suggest?

[Skimask]

some simulations

Using Proteus simulator

The problem is that when I run the simulation

It's been so long since I typed a code

Just one code?

What do you suggest?

Buy some real physical hardware and forget the simulators...

[Kjelt]

I personally always ground the emitter of a npn transistor and place a resistor in series with the supply and the collector.
Then place the input of the microcontroller at the collector and it should be '1' when optocoupler is off and '0' when on.

The forward current and typical voltage for the LED of the 4N25 are 50 mA

sounds more like a maximum current then typical, at 5mA - 10mA it should already conduct.

[villager]

I tried doing the pull-up resistor but it changes nothing. I used the voltmeter to see if there's voltage between the terminals of the pull-down resistor when I press the button, and yes, there's around 4.9 volts. When the button is not pressed, it reads 0 volts of course. It's really weird. Could it be a problem with the simulator? I look for other answers.