Parts
| 1× | NE555 timer DIP-8 (TLC555 for 3 V) |
| 1× | 8-pin IC socket DIP-8 (for the soldered version) |
| 1× | Resistor RA 10 kΩ (brown, black, orange) |
| 1× | Resistor RB 68 kΩ (blue, grey, orange) |
| 1× | Capacitor C 10 µF, 16 V or more, electrolytic |
| 1× | Capacitor 100 nF ceramic (104) (across pins 8 and 1) |
| 2× | Red LED, 5 mm about 2 V |
| 2× | Resistor 470 Ω (yellow, violet, brown) (9 V; see 5 V values) |
| 1× | 9 V battery + clip PP3 alkaline |
| 1× | Breadboard or stripboard |
Wiring
| Pin 8 and pin 4 | → +9 V |
| Pin 1 | → Ground (battery −) |
| 100 nF | → Pin 8 to pin 1 |
| 10 kΩ (RA) | → +9 V to pin 7 |
| 68 kΩ (RB) | → Pin 7 to pin 6 |
| Pin 6 | → Pin 2 |
| 10 µF | → Pin 2 to ground (stripe to ground) |
| Pin 3 | → 470 Ω → LED A anode; cathode to ground |
| +9 V | → 470 Ω → LED B anode; cathode to pin 3 |
Steps
| 1 | Place the 555 and its power | Check: 9 V between pin 8 and pin 1 |
| 2 | Add the timing parts | Check: Pin 2 and pin 6 joined; capacitor stripe to ground |
| 3 | Fit the two LEDs on pin 3 | Check: Both LEDs light when you touch their leads to the supply by hand |
| 4 | Power up and time it | Check: About 30 flashes in 30 s |
| 5 | Change the speed | Check: Rate changes in the direction you expected |
| 6 | Solder it and fit it | Check: Flashes on stripboard exactly as on the breadboard |
Tests
| Measure | Expect | Got |
|---|
| Pin 8 to pin 1 | battery voltage, 8–9.5 V | |
| Pin 4 to pin 1 | same as pin 8 | |
| Pin 2 with a meter | swings between about 3 V and 6 V | |
| Flashes of LED A in 30 s | about 30 (25–37 is fine) | |
| Chip after 5 minutes | cold to the touch | |
