6.8 kΩ resistor color code

Where you'll meet it

Watching a 9 V battery from an ESP32

An ESP32 can measure a voltage on its ADC pins, but never more than 3.3 V, and it reads most accurately up to about 2.45 V. Two resistors scale a 9 V battery down: 6.8 kΩ from the battery's plus to the ADC pin, then 2.2 kΩ from the pin to ground.

V_out = 9 V × 2.2 kΩ / (6.8 kΩ + 2.2 kΩ) = 2.2 V

2.2 V is under the pin's 3.3 V limit and inside the range where the ESP32 reads best, even from a fresh battery that reads a little over 9 V.

The pair draws 9 V / 9 kΩ = 1 mA from the battery, small next to what a running ESP32 takes.

The 6.8 kΩ resistor turns (1 mA)² × 6.8 kΩ ≈ 0.007 W into heat, so any size will do.

In code, multiply the pin's voltage by (6.8 kΩ + 2.2 kΩ) / 2.2 kΩ to get the battery's voltage back.

The drawing shows only the battery's plus wire: its minus must connect to the ESP32's GND. Use an ADC1 pin such as GPIO34, because the ADC2 pins stop working while Wi-Fi is on. The ESP32's ADC and the resistors are both a few percent off, so check the result against a meter once and correct it in code. The pin stays within its limit for anything up to 13.5 V on the battery side.

On SMD parts

Look for 682 or 6801

• 682682 = 68 × 10² = 6,800 Ω (3-digit code).
• 68016801 = 680 × 10¹ = 6,800 Ω (4-digit code, usually ±1% parts).

There is no EIA-96 code, because 6.8 kΩ is not an E96 value (the nearest E96 values are 6.65 kΩ and 6.81 kΩ).

Check it with a meter

Read 6.46–7.14 kΩ

1. Take the resistor out of the circuit.
2. Set the meter to Ω, range 20 kΩ (or auto).
3. Touch one probe to each lead. Keep your fingers off the metal: your body is a resistor too.
4. Anything from 6.46 to 7.14 kΩ is a good ±5% part. A 5-band ±1% part should read 6.732 to 6.868 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.