What's top of mind right now when it comes to 230V AC mains voltage detection? I need to tell the digital input of the microcontroller whether mains voltage (230V AC) has been applied to a particular terminal. A circuit with an optocoupler (like a zero crossing detector)? Or maybe a very...

2 resistors as voltage divider, diode, capacitor. In SMD some tiny thing will take up as much as the optocoupler itself. Unless you need isolation from the mains, then no. Perhaps 2 transistors in a darlington circuit would be enough, the gate hanging in the air and close to the 230VAC path and it will also work. The circuit is basically the same as in voltage detectors. And if you have more current in the 230V circuit then take a reed switch, wrap it a few times with one wire from the power wire and connect it to the uC. The current in the wire will trigger the reed switch. Other than that, it is the optocoupler that leads the way.

Yes, but...... Oh, but how to connect the LED correctly to the network, i.e. the optocoupler too.

How about special photocouplers such as the SFH628A-4 TLP182? I will be testing a similar arrangement soon.

. True, I didn't take into account that the components powering the optocoupler also consume some space.

Finished PMT product on optocoupler: O.C output, that is ideally under the uC.

If galvanic isolation from the mains is not required, then 2 resistors of 1 MOm each will suffice - one between the IO pin and the wire, the other between the GND of the prock and the other 230V wire. Theoretically you can on one resistor, but usually resistors have an operating voltage up to 200V, so two will provide safe conditions. If separation is required, however, an optocoupler, necessarily with two anti-parallel diodes on the structure. There is nothing to combine in such a simple circuit.

Detection of the presence of 230V AC mains voltage - digital signal for the microcontroller

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#1 18819604 16 Jul 2020 00:15

MES Mariusz MES Mariusz

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Post #1
18819604 16 Jul 2020 00:15

What's top of mind right now when it comes to 230V AC mains voltage detection?

I need to tell the digital input of the microcontroller whether mains voltage (230V AC) has been applied to a particular terminal.

A circuit with an optocoupler (like a zero crossing detector)? Or maybe a very miniature relay with a 230V AC coil (it seems that they - with such a coil - are not miniature at all).

Or maybe there are some dedicated, specialised mains voltage detection circuits that return an adequate, low-voltage logic level that can be fed into the microcontroller input ?

Target: cheap, miniature (minimum extra PCB space), reliable.
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#2 18819612 16 Jul 2020 00:21

Anonymous Anonymous

Level 1

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Post #2
18819612 16 Jul 2020 00:21

2 resistors as voltage divider, diode, capacitor. In SMD some tiny thing will take up as much as the optocoupler itself. Unless you need isolation from the mains, then no. Perhaps 2 transistors in a darlington circuit would be enough, the gate hanging "in the air" and close to the 230VAC path and it will also work. The circuit is basically the same as in voltage detectors.
And if you have more current in the 230V circuit then take a reed switch, wrap it a few times with one wire from the power wire and connect it to the uC. The current in the wire will trigger the reed switch.
Other than that, it is the optocoupler that leads the way.
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#3 18819667 16 Jul 2020 03:28

Krzysztof Kamienski Krzysztof Kamienski

Level 43

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Post #3
18819667 16 Jul 2020 03:28

CC116 wrote:
Other than that, it is the optocoupler that leads the way.
Yes, but......
https://www.elektroda.pl/rtvforum/topic3710010.html
Oh, but how to connect the LED correctly to the network, i.e. the optocoupler too.
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#4 18819680 16 Jul 2020 05:24

Jogesh Jogesh

Level 28

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Post #4
18819680 16 Jul 2020 05:24

How about special photocouplers such as the SFH628A-4 TLP182? I will be testing a similar arrangement soon.
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#5 18820874 16 Jul 2020 18:51

Anonymous Anonymous

Level 1

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Post #5
18820874 16 Jul 2020 18:51

Krzysztof Kamienski wrote:
that is, how to correctly connect the LED to the mains, i.e. the optocoupler too.
.
True, I didn't take into account that the components powering the optocoupler also consume some space.
#6 18821073 16 Jul 2020 20:11

dariusz.bembenek dariusz.bembenek

Stationary Alarms specialist

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Post #6
18821073 16 Jul 2020 20:11

Finished PMT product on optocoupler:
https://ropam.com.pl/product/pmt/

O.C output, that is "ideally" under the uC.
#7 18825768 19 Jul 2020 14:10

tmf tmf

VIP Meritorious for electroda.pl

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Post #7
18825768 19 Jul 2020 14:10

If galvanic isolation from the mains is not required, then 2 resistors of 1 MOm each will suffice - one between the IO pin and the wire, the other between the GND of the prock and the other 230V wire. Theoretically you can on one resistor, but usually resistors have an operating voltage up to 200V, so two will provide safe conditions. If separation is required, however, an optocoupler, necessarily with two anti-parallel diodes on the structure. There is nothing to combine in such a simple circuit.
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Topic summary

The discussion centers on methods for detecting 230V AC mains voltage for microcontroller input. Various solutions are proposed, including using an optocoupler, a voltage divider with resistors, and a reed switch activated by current in a nearby wire. Special photocouplers like SFH628A-4 and TLP182 are suggested for testing. If galvanic isolation is not necessary, a simple circuit with two high-value resistors can suffice, while an optocoupler with anti-parallel diodes is recommended for isolated applications. The focus is on achieving a compact, reliable, and cost-effective design.
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Detection of the presence of 230V AC mains voltage - digital signal for the microcontroller

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