Parts
| 1× | Carbon film resistor kit E12, 5 %, 1/4 W (10 Ω to 1 MΩ) |
| 3× | Metal film resistor 1 kΩ, 4.7 kΩ, 10 kΩ, 1 % |
| 1× | Resistor 130 Ω, 5 %, 1/4 W (5 V green LED) |
| 1× | Resistor 510 Ω, 5 %, 1/2 W (12 V red LED) |
| 1× | 5 mm green LED VF max 2.5 V (WP7113SGC or similar) |
| 1× | 5 mm red LED VF max 2.5 V (WP7113SURDK or similar) |
| 1× | Breadboard and jumper wires half size |
| 1× | 5 V supply USB adapter or bench supply |
| 1× | 12 V adapter any, 0.5 A or more |
| 1× | Multimeter Ω and DC V ranges |
Wiring
| +5 V | → 130 Ω → green LED anode (long leg) |
| Green LED cathode (flat side) | → GND |
| +12 V | → 510 Ω, 1/2 W → red LED anode |
| Red LED cathode | → 12 V GND |
| Meter (DC V) | → across each resistor |
Steps
| 1 | Work out the value | Check: Value worked out from the maximum VF (125 Ω here) |
| 2 | Round to a value you can buy | Check: Next E24 value up (130 Ω), current under the LED's maximum |
| 3 | Choose the tolerance | Check: 5 % for LEDs and pull-ups, 1 % for dividers and timers |
| 4 | Check the power | Check: I² × R at or under half the rating |
| 5 | Allow for the heat inside the box | Check: Power still under half the derated rating at box temperature |
| 6 | Check the voltage on high values | Check: Voltage across the part under its working-voltage limit |
| 7 | Read the marking, then measure | Check: Meter reading inside the tolerance band |
Tests
| Measure | Expect | Got |
|---|
| Each resistor, out of circuit (Ω) | inside its tolerance band | |
| Volts across 130 Ω ÷ 130 | 19.2 to 21.5 mA | |
| Volts across 510 Ω ÷ 510 | 18.6 to 19.7 mA | |
| 510 Ω after 10 minutes | warm, not too hot to touch | |
| Your circuit: I² × R ___ | under half the rating | |
