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Help with optocoupler optocoupler connect to schmitt trigger 74HC14

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fcb:
We don't know what your end goal is? examples:

a. If you are building a PLC or something similar and cost is an issue, I wouldn't bother with 74xx device at all, just the pull-up resistor and wack it straight into the microcontroller (do you need the LED?).
b. If you need to 100 channels of this then I'd scan them with perhaps a bunch of 4051's, each with it's own pull-up resistor on the output.
c. If it's purely educational, then stick with an LED and gate. 
d. If it's a commercial device, does cost factor? size? assembly time?

I'm all for helping, but some idea of what your goal is will help.

Also, if the purpose of your 74xx to MCU resistor is to current limit, i'd make it more like 10K - as you've probably got multiple channels going into the MCU and if you misconfigure one channel, you are likely to misconfigure a whole ports worth.  Again, some idea what your goal is will help.

StillTrying:
It never fails to surprise me how much is going on in even just 4 or 5 components, especially when you start to tune them to accept a suitable range of input and output. 8)

The low power LED indication seems to be sorted.

"We don't know what your end goal is?"
Yep.

We still don't know enough about the 24V input, it needs defining to get much further.
Max. 100Hz 24Vpp square waves?
Should a 2ms wide 18V pulse be counted as a switching or rejected as noise?
Could 2ms wide pulses more easily be rejected by the software as noise?

Danesh_SA:
Thanks all for your replys,
My goal is to design a kind of DAQ and it will be open source in future.it has 4-8 isolated digital input.(Low speed),many sensors in industry are  PNP or NPN ,there is link below of proximity sensors:
http://www.ia.omron.com/products/category/sensors/proximity-sensors/

My responsibility to engineering is to consider many situations and design really good product with considrable price,i see many of designs on net ,and they made without thinking and they are just copy and paste!anyway,@fcb really thanks for your attention about (a..d) situtions,i consider many of them ,i.e: I see design's from siemens and rockwell and ... ,many of them use Schmitt trigger IC after optocouplers ,and im interested to use it in my design ,and i want to know how it works and design my DAQ digital input with good protection level(i.e : I say maybe someone accidentally configure the MCU as output in low level and i don't want the circuit functionality fails.)

@StillTrying,@fcb so i change R4 to 10K . green LEDs for input indicator, as R3 is 1k ,the current draw from 7414 will be a little(1mA each channel ) and i think its OK  ;)

StillTrying:
 "so i change R4 to 10K"

I'd leave it at 1k for speed and noise reasons. :)

It's easy to roughly estimate the dissipation(s)  if/when the 2 outputs were trying to pull in different directions thorough the 1k.

With a 3.3V supply there'd be about 2.8V across the 1k = 2.8V x 2.8mA = 7.8 mW, that's never going to harm the 1k.
For the output(s) themselves 2.8mA x 0.5V = 1.4 mW, that's never going to harm the outputs.

You could have that 1k even a bit lower, - but might stop the dim LED lighting when the outputs were fighting!

I'd concentrate on the 24V input's minimum acceptable voltage, maximum safe voltage protection ?

Danesh_SA:
Dear StillTrying,
Thanks for response,
Now i got it why 1k is reasonable value ,i can use 0603 package comfortably. :)
I Know the better option is use another Driver for indicator LEDs but because of price ,i think its a good and stable design to connect both of them(LED ,MCUIN1) to 7414's output.
1-you do this "With a 3.3V supply there'd be about 2.8V across the 1k = 2.8V x 2.8mA = 7.8 mW, that's never going to harm the 1k.
" for worst case scenario(outputs were fighting),and i think the 2.8mA came from (1.4mA -(- 1.4mA)) -> current going through R3 ,when the outputs are fighting.Is it right?
2-I keep R4 ,1k as i say above and you mention it.:-+
3-The maximum safe voltage will be about Vc=45v(i use TVS).

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