🔊 Loud/Polite Doorbell

What you're building

A doorbell with a loudness selector. Press the ring button and one of two things happens depending on where a small slide switch is sitting:

• Slide open (polite mode): the buzzer beeps as a scratchy whisper — a real active buzzer might just click or fall silent entirely at this current.
• Slide closed (loud mode): the buzzer beeps at the same full ~30 mA volume as Pocket Beeper — the "wake the house" version.

The clever part is how the slide switch changes the volume: it doesn't add or remove a resistor by moving one physically. It sits in parallel with a 1 kΩ resistor and, when closed, gives the current a shortcut around it — so the 1 kΩ effectively disappears from the loop. Open the slide and the current is forced back through the 1 kΩ. That "shorting a resistor with a switch" pattern is a real design trick you'll see in phone volume switches, guitar tone controls, and vintage stereo equipment.

The big idea: switches in parallel with a resistor are bypasses

Every switch you've used so far has sat in series with something — in Pocket Beeper the button was in series with the buzzer, so opening it broke the loop. Here the slide switch is doing something new: it sits beside the 1 kΩ resistor, both between the same two breadboard nodes.

• Slide open. The slide is an ~infinite Ω "wire that isn't there". Current has only one road forward — through the 1 kΩ. The 1 kΩ is the loop.
• Slide closed. The slide is ~0 Ω. Current sees two roads: one through 1 kΩ, and one through ~0 Ω. It overwhelmingly takes the ~0 Ω road, because current flows the easy way. The 1 kΩ still exists, but almost no current goes through it — it is bypassed. The loop behaves as if the resistor isn't there at all.

That gives you a way to add or remove a resistor from a loop without physically moving anything. Two states of a slide switch give you two very different loops.

Do the math

Loop while the ring button is pressed:

battery + → button → (1 kΩ ∥ slide) → buzzer → battery −

The active buzzer behaves like a ~150 Ω load at 4.5 V (from Pocket Beeper).

Polite mode (slide open):

• Only the 1 kΩ road is available, so total loop resistance is 1000 + 150 = 1150 Ω.
• I = V ÷ R = 4.5 V ÷ 1150 Ω ≈ 0.0039 A = 3.9 mA.
• Active buzzers need a few milliamps of drive to make a proper tone. 3.9 mA is right at the edge — you'll hear a scratchy whisper, a click, or sometimes nothing at all. This is the same "starved buzzer" behaviour you met in Two-Tone Doorbell and Whisper Alarm, in a simpler build. A series resistor does not reliably make an active buzzer quieter. Use it to mute, not to dim.

Loud mode (slide closed):

• The slide short-circuits the 1 kΩ, so the loop is effectively just buzzer = 150 Ω.
• I = V ÷ R = 4.5 V ÷ 150 Ω = 0.030 A = 30 mA.
• Full-volume beep, the same as Pocket Beeper and Doorbell.

The current jumps by nearly 8× just by flipping one switch that doesn't touch the buzzer or the button at all. That is a genuinely useful design pattern.

Build it

1. Power rails. Battery + → top of the board (row 1, say). Battery − → bottom row.
2. Top rail row 1: + rail → push button → 1 kΩ resistor → wire → the buzzer's + leg.
3. The bypass detour. Just above the 1 kΩ, on a higher row, route: wire up from the node before the 1 kΩ → slide switch across → wire down to the node after the 1 kΩ. The slide and the 1 kΩ now sit in parallel, sharing the same two nodes.
4. Buzzer. Long leg (+) to the wire coming off the 1 kΩ / slide junction; short leg to the − rail.
5. Test both modes, in order:
   • Slide open, press the button → a scratchy whisper (or silence — that's honest).
   • Slide closed, press the button → full-volume beep, same as Pocket Beeper.

Why this is different from Dial-a-Buzz

Dial-a-Buzz used a potentiometer in series with the buzzer to choose any current between 30 mA and ~0.5 mA — a knob with a whole range. Loud/Polite Doorbell is only two positions: full on or starved. That's simpler to build, cheaper (a slide switch costs less than a pot), and — because you only ever want "loud" or "quiet" for a doorbell — usually the right design. In real products this is why so many things have a "night mode" switch instead of a volume knob: two useful states beats infinitely many that no one would sit and adjust.