Opto Isolated Input

Archive
1

Hello,

I need read some signal from a lot of photocells from an industrial machine.

For safety reasons i need read it but i need an isolated read.

My project is like an mini industrial PLC. For this reason i prefer bricks or boards, not soldering components.

i have seen something like 

http://www.cubloc.com/product/01_03ssr8.php

or

http://arduino-direct.com/sunshop/index.php?l=product_detail&p=156

but my requeriments are.

input between 3 and 30 VDC

output between 3.3 and 5 VDC.

My idea is read a 24 VDC input and have an optoisolated signal in my Panda II board.

Can you suggest some board or brick, or similar ??

thanks in advance.

http://www.lafabricadesoftware.com
http://www.lavanderiacobos.com

2

In the past I have use:
http://www.ereshop.com/shop/i2c-opto-input-based-on-pcf8574a-p-602.html?zenid=0cc6ca3426200d61aa4bb4dd31440d10

and

http://www.lightsosoft.com/node/21

Both are I2C serial input boards. Both are only rated for 12VDC, but with a resistor change can do 24V. I’m not sure you can get down to 3v all that easily though - you have to take the voltage drop across the diode inside the opto-isolator into account so you would be down to 1.5v - pretty low. The problem with that is if you size your current-limiting resistor for 30vdc, you won’t get very much forward currrent down at 3v. We are building one now, with a 4.2k resistor, indicating LED and opto isolator led in series, the minimum input voltage to turn on the opto is 7.8VDC. Assuming no indicating LED, we would still need 6.3 VDC to turn on with that size resistor.