part · Level 1 · Light · input
How a tactile push button works
Push button (tactile) — A switch that only stays on while you press it.
What it is
A tactile push button is a momentary switch: it only connects while your finger is on it. Let go and a spring inside pops the contact open again. The "tactile" part is the click you feel — a little metal dome snapping over.
Yours has four legs, which confuses everyone at first. They are two pairs. Legs on the same side (the side where the legs bend outward) are permanently joined; pressing the button connects one pair to the other. So it is really a two-terminal switch with each terminal brought out twice, to hold it steady on the board.
Sit it across the breadboard's middle groove and the pairs land on separate strips automatically.
How it works
Electrically it is the same as any switch: pressed ≈ 0 Ω, released = an open gap. In the Morse Code Messenger the loop is + → button → 220 Ω → yellow LED → −, so pressed gives (4.5 − 2.0) ÷ 220 ≈ 11 mA and released gives 0 mA. Your dots and dashes are just how long that 11 mA flows.
Two buttons can make logic without a chip:
- In series (one after the other): current only flows when both are pressed. That is an AND — The Vault.
- In parallel (side by side, both feeding the same lane): either one completes the loop. That is an OR — the Panic Doorbell.
Because a button drops 0 V, adding it to a lane changes nothing about the resistor maths. The LED still needs its 220 Ω; the button just decides when.
Contacts inside bounce for a few milliseconds when they close — too fast to see with an LED, but it matters later when a microcontroller counts presses. That is called bounce, and Level 7 deals with it in code.
The numbers
| Legs | 4 (two pairs) — same-side legs are already joined |
|---|---|
| Action | momentary — on only while held |
| Resistance pressed | ≈ 0 Ω |
| Contact rating (typical) | ≈ 50 mA — fine for LEDs and a buzzer |
| Bounce time | ≈ 1–10 ms — matters for code, not for LEDs |
See it working
The Morse Code Messenger circuit, simulated live. Open it on the Workbench to change anything.
simulating…
Mistakes everyone makes
- Wired to two legs that are already joined. The LED stays on whether or not you press. Fix: use legs on opposite sides, or sit the button across the groove and use one leg from each side.
- Legs on the same strip row on one side of the groove. You have shorted the button out. Fix: rotate it 90° — the bent legs should point along the groove.
- Button "sticks on". Its legs are bent and touching. Fix: straighten them; push it in flat.
- Expecting it to stay on. It is momentary by design. Fix: use the slide switch for on/off.
Questions people ask
- Why does a push button have 4 pins?
- For stability. Two pins are joined together on each side; pressing connects one pair to the other. Use one pin from each pair, or sit it across the breadboard groove.
- Why does my LED stay on without pressing the button?
- The two wires are on pins that are permanently connected (the same pair). Move one wire to a pin on the other side of the button.
- How do I make two buttons that both have to be pressed?
- Put them in series — the output of one feeds the input of the other. Current only flows when both are closed. That is an AND gate made from switches.
Projects that use this part
- 📡 Morse Code Messenger — A push button, an LED, and a secret code — send real messages with light. L1 · 20 min
- 🔐 The Vault — Two buttons, one loop — the LED only lights when BOTH are pressed at the same time. L1 · 15 min
- 🚨 Signal Light — A slide switch and a push button in parallel — the slide is the steady beacon, the button is the extra flash. Either lights the lamp. L1 · 15 min
- 🛟 Escape Hatch — The Vault with a big red emergency button wired around both locks — turn BOTH keys, or hit the button, and the light comes on. L1 · 20 min
- 🔔 Door Buzzer — Your first sound circuit — a real doorbell for your bedroom door. L2 · 20 min
- 🚨 Panic Doorbell — Two buttons wired so either one fires the same buzzer and light — your first OR gate. L2 · 20 min
- 🔈 Whisper Alarm — A doorbell with a volume knob — the pot lives in the buzzer lane, so twisting it changes the beep without touching the light. L2 · 25 min
- 🛎️ Two-Tone Doorbell — Two call buttons, one doorbell: LOUD rings the buzzer and lights the porch LED; QUIET starves the buzzer and shows why it can't just be dimmed. L2 · 25 min
- 🚨 Arm & Ring — A doorbell that ignores you unless a hidden slide switch is armed first — series-AND with sound, plus an 'armed' LED that shows the state. L2 · 20 min
- 🔔 Twin Bells — One doorbell button rings two buzzers in parallel — one in your room, one in the kitchen — with a slide switch that mutes just the bedroom bell at night. L2 · 20 min
- 🖐️ Two-Hand Bell — Two push buttons in series feeding a buzzer and an LED — both hands must stay pressed for the alarm to sound. L2 · 20 min
- 🔕 Silent Alarm — Three panic buttons wired in parallel, all inside an armed lane — any one of them fires the buzzer, and a small LED tells you the alarm is watching. L2 · 25 min
- 🎮 Quiz Buzzer — Two teams, two big buttons: yours lights your LED and rings your buzzer, theirs does the same on their side. Two independent doorbells sharing one battery. L2 · 20 min
- 💨 Handheld Fan — Press the button, the fan spins. A tiny finger current commands a hundred-milliamp motor through a transistor. L4 · 20 min
- 🆘 Panic Fan — Two buttons, either one fires the fan. Panic Doorbell wearing a motor — an OR gate that spins. L4 · 20 min
- 🎉 Party Spinner — One button, three mouths: a spinning motor, a red LED, and a buzzer all fire together. One transistor drives them all. L4 · 25 min
- 🚗 Twin Wheels — Two motors from one button — a Level 9 robot drivetrain, five levels early. L4 · 25 min
verified against: SparkFun — Switch Basics · SparkFun — Series and Parallel Circuits · Arduino — Button (built-in example)