Capacitor Countdown Kit

Classes 5-6, typical ages 10–12. Age ranges vary by learner. Guided low-voltage electronics.

Activity engagement

60–90 minutes. Explore 10–15 min · Build 20–30 min · Test and discuss 30–45 min. Estimated time for building, testing and discussion.

What you need

No computer required. An adult helps inspect connections.

Included components

• Small Breadboard / Mini Solderless Board - 400 points — 1 breadboard
• Jumper Wire Combo - Male to Male, Male to Female and Female to Female Breadboard Connecting Wires (10 Qty Each) — 1 set
• Illustrated Activity Guide and Observation Sheets — 1 set
• Fitted Headers and Labelled Connection Leads — 1 set
• 4 CELL AA BATTERY HOLDER WITH SWITCH / COVER — 1 holder
• AA BATTERY — 4 battery (individual units)
• Regulated 5 V Power Supply with Short-Circuit Protection — 1 power supply
• 555 Timer IC (LM555 / NE555 / SE555) - 8 Pin DIP Package — 1 IC
• Tactile Push Button Switch 12x12x8mm 4-Pin — 1 button
• 100 µF CAPACITOR (5 PCS) — 1 capacitor
• 100K Ω 1/4 Watts (10 PCS) — 1 resistor
• 10K Ω 1/4 Watts (10 PCS) — 1 resistor
• 5mm LED - Red Color — 1 LED
• 330 Ω 1/4 Watts (10 PCS) — 1 resistor
• 0.01 µF CAPACITOR (5 PCS) — 1 capacitor
• 0.1 µF CAPACITOR (5 PCS) — 1 capacitor

What you learn

• A capacitor stores charge and changes voltage over time.
• A 555 monostable makes a single pulse after a trigger.
• The approximate pulse length is 1.1 × R × C.

Connection guide

• NE555 pin 1 → GND; 8 and 4 → +5 V. Add 100 nF across pins 8/1 and 10 nF from pin 5 to GND.
• Pins 6 and 7 → timing node; 100 kOhm from +5 V to that node; 100 uF capacitor positive to node and negative to GND.
• Pin 2 → +5 V through 10 kOhm; push button from pin 2 to GND. Pin 3 → 330 Ohm → LED anode; cathode → GND.

Steps to make it

1. Disconnect all power and identify the supplied part labels and pinouts before wiring.
2. Place the DIP chip across the breadboard centre gap; locate pin 1 from its notch/dot using the connection card.
3. Connect the supply and control pins, then the timing network, checking electrolytic capacitor polarity.
4. Add the trigger button and current-limited LED. Ask an adult to inspect the rails.
5. Apply regulated 5 V, tap and release the button, and time the LED pulse with a clock.
6. Repeat five trials, allowing the LED to go out before triggering again.

Test challenge

Compare the measured LED-on time with 1.1 × 100000 × 0.0001, approximately 11 seconds.

Observation task

Five pulse lengths, mean time, predicted time, and percentage difference.

Expected result

A short button press produces a much longer LED pulse; capacitor tolerance means timing is approximate.

If it does not work

Switch off and check pin numbering, pin 4 at +5 V, capacitor polarity and the trigger pull-up. Do not hold the button down while timing.

Try next

Explain why a larger timing resistor would lengthen the pulse.

Use and supervision

Use only the supplied low-voltage DC parts. Disconnect power before rewiring; check polarity and labelled pinouts. No soldering or exposed mains connections. Adult guidance is recommended.

How this experiment works

Download class activity guide

Cover illustrations show component types. Functional animations explain principles and are not recorded prototype tests. Follow the supplied connection labels and pinouts.