68 kΩ resistor color code

Where you'll meet it

Watching a 24 V supply with an Arduino

3D printers, LED strips and many motor projects run from a 24 V power supply. To let an Arduino keep an eye on it, two resistors scale it into A0's 0 to 5 V range: 68 kΩ from the supply's plus to A0, then 12 kΩ from A0 to ground.

V_out = 24 V × 12 kΩ / (68 kΩ + 12 kΩ) = 3.6 V

3.6 V is safely under A0's 5 V limit. The most A0 can read, 5 V, stands for about 33.3 V, so a supply set a little high still fits.

The pair draws 24 V / 80 kΩ = 0.3 mA, which no 24 V supply notices.

The 68 kΩ resistor turns 20.4 V × 0.3 mA ≈ 0.006 W into heat, so any ¼ W part is fine.

The drawing shows only the supply's plus wire: its minus must connect to the Arduino's GND. In code, multiply the voltage at A0 by 80 / 12 to get the supply's voltage, and check once against a meter, because resistor tolerances shift it by a few percent. Seen from the pin, the pair looks like about 10.2 kΩ, right at the 10 kΩ the Arduino's analog input is designed for; a 100 nF capacitor from A0 to GND keeps the readings steady.

On SMD parts

Look for 683 or 6802

• 683683 = 68 × 10³ = 68,000 Ω (3-digit code).
• 68026802 = 680 × 10² = 68,000 Ω (4-digit code, usually ±1% parts).

There is no EIA-96 code, because 68 kΩ is not an E96 value (the nearest E96 values are 66.5 kΩ and 68.1 kΩ).

Check it with a meter

Read 64.6–71.4 kΩ

1. Take the resistor out of the circuit.
2. Set the meter to Ω, range 200 kΩ (or auto).
3. Touch one probe to each lead. Keep your fingers off the metal: your body is a resistor too. At 68 kΩ this matters: two fingers on the leads can pull the reading down.
4. Anything from 64.6 to 71.4 kΩ is a good ±5% part. A 5-band ±1% part should read 67.32 to 68.68 kΩ.

A meter has a small error of its own, so a reading a hair outside the range does not prove the part is bad. Measure again with firm contact before you swap it.