Triggering Raspberry Pi GPIO with 127V AC

Question

I'm building a home automation system with raspberry pi and would like to trigger it with a regular pulse switch, connected to my home's 127V AC power network. I'm doing this so I don't need to rewire my power outlets.

I came up with a circuit like this. Do you guys think it would work?

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Thanks!

Edit 1: Here's what I'm trying to achieve:

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The switch is far away from the raspberry and the wiring is already in place, that's why I would like to use 127V.

Edit 2: deleted

Edit 3: new diagram:

enter image description here

• Sanmveg saini: Please, can you explain more? What I understand is that you want to interrupt rpi whenever pulse from "pulse switch" would cross trough 0 Volts. Am I correct?
• frarugi87: You can attach it directly; you will for sure "trigger" it, at least once... (note: DON'T do it... the "at least once" part means it will blow up in a "not so nice" way)
• Janka: Use an optocouple, for the love of god!
• Tony Stewart EE since 1975: The 50k resistor might easily flashover with a 6kV transient rated for 500V and get rather warm.
• Alexandre Giuseppe: @Janka, thanks, updated with your suggestions. The problem of moving the GPIO to the collector is that this makes it 1 when the optocoupler is disabled. Also, I'm using different grounds for the left and right side, so I didn't join them.

Answer 1

Sometimes the people just use a 1M resistor in series with the power; personally I'd also add a small zener to reduce risks

schematic

^{simulate this circuit – Schematic created using CircuitLab}

However, personally I don't like this. Remember that in this case the ground is tied to the neutral wire, and so the rPI is no more insulated. This is usually a thing I want to avoid with microcontrollers, and much more with a complex system like a rPI which gets attached to a lot of other stuff.

For this reason I highly suggest you to avoid this, and use a proper optocoupler. For instance I have used in the past cheap optocouplers (PC817) to sense the presence of the 230V signal. I suggest you to search for circuits with optocouplers (in my case, I used the optocoupler, a diode to block reverse wave, and 100k resistor(s) to limit the current (in your case you may reduce the value of the resistors). This way high voltage and low voltages are properly separated.

My (slightly different) circuit is in this other question, but there are plenty of them. Note: you will have a 50Hz wave there, so you shall filter it either in SW or in HW

• Voltage Spike: The above circuit is not safe in the event of a failure or arcing, make sure you use an optocoupler for saftey.
• Alexandre Giuseppe: Can you please provide some input on my optocouple design? Thanks.
• tomnexus: Yes :) See also my question and some answers here: raspberrypi.stackexchange.com/questions/31648/…