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I have two main questions regarding the electromagnetic compatibility (EMC).

  1. If I develop an electronical device and market it in Europe, it needs to be EMC-compliant, right? How come I can buy European devices which are not EMC-compliant? Do the devices truly need to pass the EMC test to be certified?

  2. Let's say I have to develop a system with a microcontroller which retrieves data from a sensor. The sensor is outside of the PCB, and I have to use a wired communication between them. For instance, temperature sensors are usually accessed through I2C. However, transmitting I2C through a cable will not pass the EMC (and maybe not even work if the cable is too long). I can use an I2C buffer to make it work but still it will not pass the EMC. Is it necessary to convert the data to another protocol (RS485, RS422, RS232, CAN...)? Does it mean that each external sensor would need its own microcontroller? I find it a bit onerous, are there other solutions?

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    \$\begingroup\$ Use shielded cable \$\endgroup\$
    – Dirk Bruere
    Dec 4, 2020 at 14:28
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    \$\begingroup\$ Why do you assume passing I2C over a cable would not pass EMC? \$\endgroup\$
    – Justme
    Dec 4, 2020 at 14:45
  • \$\begingroup\$ I was working with a society specialized in EMC : they review your electronical card and tell you what to modify for the system to be EMC-compliant (or at least, to have a chance to be EMC-compliant ^^). They have told me that passing I2C over a cable will not pass the EMC. Regarding shielded cable, the ground shield have an efficiency only when it is connected to a metallic housing, which is not my case. \$\endgroup\$
    – AladdinSane
    Dec 4, 2020 at 15:53
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    \$\begingroup\$ @AladdinSane "passing i2c over a cable will not pass the EMC" - that is not true in general! In my company we have a whole product family that involves i2c on 4m cables and we passed EMC tests at different third party labs. \$\endgroup\$
    – Sim Son
    Dec 4, 2020 at 17:31

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  1. Yes. Depending on the application, it needs to conform to the EMC or the RED directive. These directives allow a form of self-certification for CE marking, so most products don't necessarily have to pass an EMC test by a 3rd party neutral test house.

    Devices put on market must have the CE mark and a declaration of conformity, where you state that the product is EMC compliant. If the product is actually EMC compliant is another story...

  2. Hard to answer since distance, baudrate and type of cable makes all the difference here. You have to be far more specific. For simpler sensors, it is very common to use 4-20mA current loops rather than CAN etc.

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  • \$\begingroup\$ Thanks ! For more details : the temperature sensor is access with I2C. The frequency is 100 kHz. Would it be better not to be standard and work with a lower frequency ? 4 wires would pass through the cable : VCC, GND, SDA and SCL. The distance would be 1 meter. \$\endgroup\$
    – AladdinSane
    Dec 4, 2020 at 15:56
  • \$\begingroup\$ @AladdinSane 1 meter could be possible with I2C, though ideally you'd use a lower baudrate still and shielded cables. Notably, shielded cables is a much more expensive solution than de-centralized microcontrollers with CAN... \$\endgroup\$
    – Lundin
    Dec 7, 2020 at 7:20

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