Consider a redesign using a spring-return / push-pull solenoid about pi-bell-slapper HOT 12 CLOSED

(Idea from comment: https://www.youtube.com/watch?v=Etr7uIL9spg&lc=UgxKTLrzPYfF4dLlNcR4AaABAg.9HHklQ8r4_v9HI7jTzobpe)

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Going to try my luck with this soon. I have a solenoid, but forgot to order a second call bell since the first is still in continuous operation :)

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A couple more things I've seen recently, for inspiration:

• How Doorbells Work
• Email Notification Bell

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To provide the ~600mA current at 5V for the solenoid, I'll probably need to power it off the Pi's 5V rail instead of through GPIO directly, since according to this answer, the 3.3V rail can only drive ~50mA... more research required.

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This circuit looks like a good guide: Pi 3 B+ 5v solenoid push-pull.

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I'm also needing to design a new enclosure/case for the thing... was going to do some measurements and start building things up by hand... but it looks like @tenderlove already did some of that work for me: https://github.com/tenderlove/analog-terminal-bell/tree/master/case

I'm thinking of modifying that design to house everything below/inside the bell... if I can route the solenoid that way.

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Some code:

import RPi.GPIO as GPIO
import time

# Use GPIO pin numbers instead of physical pin numbers.
GPIO.setmode(GPIO.BCM)

# Set GPIO pin 4 as the output.
GPIO.setup(4, GPIO.OUT)

# Set GPIO 4 high and then back low to ding the bell.
GPIO.output(4, GPIO.HIGH)
time.sleep(0.05)
GPIO.output(4, GPIO.LOW)

# Cleanup.
GPIO.cleanup()

Save that to a file like ding.py and also make sure your user has permissions to control GPIO with sudo adduser pi gpio and logging out and logging back in (else you'll get a warning RuntimeError: Not running on a RPi!).

Then run:

python ding.py

This should light up GPIO pin 4, and cause a ding, using the circuit in this comment: #2 (comment)

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It verks!

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Just noting this for myself: For the Pi Zero W, it requires 32-bit Pi OS (since the CPU is not 64-bit capable), and it only works on 802.11b/g/n at 2.4 GHz (no 5 GHz networking). With that out of the way, I can get it tested and working now :)

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Next step: Learning OpenSCAD...

Found Mastering OpenSCAD (paperback version here) after a mention by @rcarmo on Twitter.

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Almost everything is perfect... but the USB port in the current version (above commit) is a hair off center to the right. Have to move it back left so larger USB cables fit through correctly.

Someday if I design a proper PCB / HAT, I can make the tolerances much slimmer. For now it works with a simple small hacked-together protoboard.

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