INPUT interfacing - optocoupler alternative?

[darksir]

HI boys,
please, can you help me?

To this day I use optocoupler PC817 to interfacing atmel or pic input with other devices - switches, relay contacts, etc.
Now I make redesign of pcb and need smaller size. pc817 is very big. I need some another circuit such as transistor, zener diodes etc. Connection will be same - switch NO NC, or contact of relay from alarm sensors.

ciruit must be good functional with interference or long cables to switches.

Any ideas, or schematics of some industrial producted alarm or IO board?

Many thanks,
Petr

 

[tpetar]

If you better look in optocoupler, inside on one side is transistor with optical control of his base. If you need small size you can use some adequate ratings SMD SOT-23 transistor and his base control by adjusted input signal which you use on LED side of optocoupler. But you should know that then you dont have isolation of circuit

For alarm centrale sensors I always use optical isolation.

 

[darksir]

Many thanks.
Yes, I need optocoupler alternative. I don´t need isolation, but good immunity for interference. I have some good experience with connection this cables directly to IO pin of MCU. This direct connection can give interference to MCU and this will reset, etc. For this reason I Looking for input circuits which are used in alarms, that have long cables to detectors and are good resistant to false impulses, static, induction, etc.

 

[tpetar]

Your needs is for optocoupler and twisted pair cables, acording to your previous post. But if you want to eliminate optocoupler you can experiment with transistor just like I mention in my post #2.