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I’m connecting a NO reed sensor to 3.3v and GPIO17. In my code I defined GPIO17 as input and set the internal resistor to pulldown.

When the door is closed, GPIO 17 reads 1 and 0 when the door is open.

The code works flawless and does what I want it to do, but since the door is closed 99% of the time I’m concerned about safety and power draw.

Is this circuit safe, or is there a risk of damaging the pi? Since there is not any resistor in the circuit, how much power does it draw?

EDIT #1

I've changed my setup to this as suggested by Milliways Reed Circuit

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This would be "safe", but not best practice and subject to interference.

The internal pullups are very high impedance; use a lower value resistor. Unless the leads are very short and/or shielded you are likely to pick up inteference.

It is hazardous running leads connected to 3.3V, any accidental short risks blowing up the regulator - it is normal to connect switches between GPIO and Gnd

See https://elinux.org/RPi_GPIO_Interface_Circuits.

It is also good practice to use a series resistor ~1kΩ to protect the GPIO if it is configured as output.

See I am getting ghosting/bouncing on my digital input

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  • I haven't had any problems with interference, but I still changed the circuit as described. Can you take another look at it to see if that's what you meant?
    – Unkn0wn
    Apr 22, 2020 at 7:10
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    That looks OK. I would have used a lower pullup 4.7kΩ max - 3.3kΩ would only draw 1mA. I guess after 50 years working on electronics is hostile environments I have learned the hard way.
    – Milliways
    Apr 22, 2020 at 7:22

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