Better options then an Optocoupler?

[The-Kevster]

Hi all!

I have a 32V switch which I want to use as an input into a RaspberryPi. The power supply is rated for 28V but I measured it at 32V. It drives a large motor so I am guessing it will drop to 28V when in use but just in case am planning for 28V-32V :grin: As the Pi will only accept a 3.3v input and is running from a separate power supply I thought using an Optocoupler might be the best idea.

As I have 6 switches in total I want to use 3 2-channel optocouplers.
http://uk.rs-online.com/web/p/optocouplers/7613552P/
**broken link removed**

The issue is to bring 32V down to 1.5V <60mA I would need to use a 560k 2W (at least) resistor which seems very excessive.

Is there a better option or will using such a high resistor be perfectly fine?

Thanks for any help!
Kev

 

[FvM]

You mean 560 ohm, not 560k. And you can drive the LED with a considerably lower current like 5 or 10 mA, either accepting a lower output current or using optocouplers with higher current transfer ratio.

60 mA is in fact the absolute maximum rating of the said optocoupler which must be never exceeded. Currents assumed for typical data are 16 or 20 mA, and lower currents are possible.

P.S.: MCT61 has a minimal CTR of 50% so you get minimal 2.5 mA ouput for 5 mA LED current, should be fine for most applications.