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I would like to find a way to sense (or detect) current through an opto-coupler. This opto is used to power an electromagnetic brake, but depending on the type of brake the current through it can range from 400mA to 1500mA.I want an opto-isolated digital signal to verify current is within a specified range in an electromagnetic brake circuit. The electromagnetic brake current can range from 400 mA to 1500 mA.

How do I detect this current safely and provide an isolated signal to the microcontroller? It could also be a current present/not present detection system. The reason behind this is somehow detecting that the brake is powered (current is flowing) or not.

Thanks!

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  • \$\begingroup\$ It's very unclear what you're trying to do. Is the opto used between MCU and a driver driving a brake to turn the brake on and off, or is it used to verify whether the brake is being powered and send a status signal back to the MCU? To do both will require two optos. \$\endgroup\$
    – Neil_UK
    Feb 19, 2021 at 15:35
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    \$\begingroup\$ What is an electromagnetic break? Perhaps a nap in a dark room? Or did you mean brake? \$\endgroup\$
    – glen_geek
    Feb 19, 2021 at 15:35
  • \$\begingroup\$ @Neil_UK yes, Neil, correct. I have a MCU driving an opto which is used to power the brake. If for some reason the brakecurrent isn't flowing I'd like a way to detect this so I won't fry my motors. \$\endgroup\$
    – Alex Er
    Feb 19, 2021 at 15:45
  • \$\begingroup\$ @glen_geek, thanks Glen, that's exactly what I mean. \$\endgroup\$
    – Alex Er
    Feb 19, 2021 at 15:46
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    \$\begingroup\$ @AlexEr, your wording is causing some confusion. How you are switching on the brake is irrelevant so leave it out of your question. Please check the edit I have made is correct and delete the strikeout text or my text as appropriate. \$\endgroup\$
    – Transistor
    Feb 19, 2021 at 17:51

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Probably the most non-invasive way is to eschew the optoisolator idea and use a Hall current sensor. There are various options, from small QFN parts that have an input loop built into the chip up to packaged parts that you simply pass a cable through. LEM, Mexlexis etc. are manufacturers.

Output tends to be in the 100-400mV/A range so you'd also need a comparator or to use an ADC and make a decision based on the value you read. Make sure the DC drift is compatible with your application (that it cannot give a false indication at the minimum current).

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