[Moved] opto transistor npn assembly

[bagusdj]

hey guys, im trying to assembling 4n26 opto transistor for zero cross detector. i configure it this way. zcd is going to my mcu external interrupt.

if i used 10k on R1, i will get voltage in zcd in amount of 3v. with this resistor, the time required to form a zero cross square wave is huge.

i tried to use 820 Ohm on R1, the time required for pulsing is less, but voltage that flows through zcd is about 0.8V.

for AT89S52, what is the minimum voltage required to trigger external interrupt? in data sheet it only mentions operating voltage for mcu is 4-5.5V

 

[pwdixon]

Re: opto transistor npn assembly

What voltage is your input signal waveform?

 

[bagusdj]

Re: opto transistor npn assembly

What voltage is your input signal waveform?

you mean voltage applied across R1? it is 8Vdc

 

[pwdixon]

So your input is about 10V or 12V peak I guess.
Is the input a sinewave or a squarewave?
Define 'huge time'.
On the input required to fire an interrupt, you need to read the processor datasheet the answer will be there.

 

[betwixt]

Why are you using an opto-coupler anyway? You would get better timing (lower voltage detection) if you just used an NPN signal transistor.

Brian.

 

[bagusdj]

So your input is about 10V or 12V peak I guess.
Is the input a sinewave or a squarewave?
Define 'huge time'.
On the input required to fire an interrupt, you need to read the processor datasheet the answer will be there.

its from transformer step down 9Vac. i search the datasheet in interrupt section but not finding info about minimal voltage to trigger interrupt.
i can say huge because i measure zcd using scope, and test is by replacing R1 with different value. the time required to form a pulse is varying. my scope is uncalibrated. but it shows that different R1 give different width of time.

Why are you using an opto-coupler anyway? You would get better timing (lower voltage detection) if you just used an NPN signal transistor.

Brian.

i just dont know about this before. i look for reference and i found it uses opto npn. so i assemble my circuit using opto npn also.

 

[pwdixon]

So the input is a sinewave. That means that the input MUST rise to above the opto LED turn on voltage before the output transistor can switch hence a delay after zero crosssover just do the maths and it will be obvious. You need an alternative switching mechanism to get closer to the actual zero crossover point I'm afraid.