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I would like to interface Arduino over SPI but need a way to decouple the system with an optoisolator. Any pointers in which optoisolator to get?

Everything works on 5V.

I've tried to connect with CNY 17-3 but it didn't work. Maybe CNY 17-3 is too slow, or something.

Datasheet CNY 17-3:

PS:

One more note, I don't need any transfer from slave so only one direction. CS, MOSI, CLK lines are needed.

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  • \$\begingroup\$ The CNN 17 seems to go to 100 kHz,and SPI can go much faster. You need to set the SPI at a slow cl9ck \$\endgroup\$ Jan 20, 2015 at 0:14

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There are digital isolators from different companies to support your application, but here I feel an important thing OP is missing, what is Insulation Rating(kVrms) you are looking for.

Based on the insulation rating Analog Devices link offers you several SPI isolators.

Not only Analog devices, you can find digital isolator from Linear Technology .

TI doesn't have dedicated link for SPI isolators, but the app note on page #5, they explain how to use their digital isolator for SPI.

Even you can look in to MAXIM link also for their digital isolator supporting SPI application.

There are some more options like IL717 from NVE isolations, link here which talks about using NVE isolators.

Even you can look into Silabs, for isolation products, but I am not sure whether they have something dedicated for SPI.

Now, the onus is on you decide which isolator you want go with, based on the availability of the product in your region and Insulation Rating and most important factor is the price if you are going for mass production.

Hope this helps you to understand the SPI isolator selection in future as well.

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SPI buses have unidirectional lines. Any good old-fashioned digital optoisolator should do the job, but you need to isolate each line in the appropriate direction.

You can certainly use an IC like the MAX14935, which will do all your lines with one chip.

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  • \$\begingroup\$ I checked all my local electronics shops and don't see anyone holding this item on stock, where could person get those.Tnx for helping out. \$\endgroup\$
    – user505160
    Jan 19, 2015 at 23:09
  • \$\begingroup\$ @user505160 element14 / newark , mouser, digikey are some online sources that come to mind \$\endgroup\$ Jan 19, 2015 at 23:38
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I am using the 4n35 optocoupler for serial and it works well. Check out this question I just asked, is the circuit I am using. Make sure to invert the resistors, because the non transistor inverts the logic.

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    \$\begingroup\$ I've updated the drawing in my answer to Joel's question to show both inverting and non-inverting circuits. \$\endgroup\$ Jan 20, 2015 at 0:05
  • \$\begingroup\$ What is the speed of 4n35, where in datasheet is this written, tnx. \$\endgroup\$
    – user505160
    Feb 3, 2015 at 18:17
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Previously i used avago's hcpl 5Mbd optocoupler series for communicating to cs5463 power meter chip (which is connected to 220v line) via spi lines. These hcpl optocoupler's are very fast but they need vcc.

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